    /* png.c - location for general purpose libpng functions
     *
     * Last changed in libpng 1.6.2 [April 25, 2013]
     * Copyright (c) 1998-2013 Glenn Randers-Pehrson
     * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
     * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
     *
     * This code is released under the libpng license.
     * For conditions of distribution and use, see the disclaimer
     * and license in png.h
     */

    #include "pngpriv.h"

    /* Generate a compiler error if there is an old png.h in the search path. */
    typedef png_libpng_version_1_6_7 Your_png_h_is_not_version_1_6_7;

    /* Tells libpng that we have already handled the first "num_bytes" bytes
     * of the PNG file signature.  If the PNG data is embedded into another
     * stream we can set num_bytes = 8 so that libpng will not attempt to read
     * or write any of the magic bytes before it starts on the IHDR.
     */

    #ifdef PNG_READ_SUPPORTED
    void PNGAPI
    png_set_sig_bytes(png_structrp png_ptr, int num_bytes)
    {
       png_debug(1, "in png_set_sig_bytes");

       if (png_ptr == NULL)
          return;

       if (num_bytes > 8)
          png_error(png_ptr, "Too many bytes for PNG signature");

       png_ptr->sig_bytes = (png_byte)(num_bytes < 0 ? 0 : num_bytes);
    }

    /* Checks whether the supplied bytes match the PNG signature.  We allow
     * checking less than the full 8-byte signature so that those apps that
     * already read the first few bytes of a file to determine the file type
     * can simply check the remaining bytes for extra assurance.  Returns
     * an integer less than, equal to, or greater than zero if sig is found,
     * respectively, to be less than, to match, or be greater than the correct
     * PNG signature (this is the same behavior as strcmp, memcmp, etc).
     */
    int PNGAPI
    png_sig_cmp(png_const_bytep sig, png_size_t start, png_size_t num_to_check)
    {
       png_byte png_signature[8] = {137, 80, 78, 71, 13, 10, 26, 10};

       if (num_to_check > 8)
          num_to_check = 8;

       else if (num_to_check < 1)
          return (-1);

       if (start > 7)
          return (-1);

       if (start + num_to_check > 8)
          num_to_check = 8 - start;

       return ((int)(memcmp(&sig[start], &png_signature[start], num_to_check)));
    }

    #endif /* PNG_READ_SUPPORTED */

    #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
    /* Function to allocate memory for zlib */
    PNG_FUNCTION(voidpf /* PRIVATE */,
    png_zalloc,(voidpf png_ptr, uInt items, uInt size),PNG_ALLOCATED)
    {
       png_alloc_size_t num_bytes = size;

       if (png_ptr == NULL)
          return NULL;

       if (items >= (~(png_alloc_size_t)0)/size)
       {
          png_warning (png_voidcast(png_structrp, png_ptr),
             "Potential overflow in png_zalloc()");
          return NULL;
       }

       num_bytes *= items;
       return png_malloc_warn(png_voidcast(png_structrp, png_ptr), num_bytes);
    }

    /* Function to free memory for zlib */
    void /* PRIVATE */
    png_zfree(voidpf png_ptr, voidpf ptr)
    {
       png_free(png_voidcast(png_const_structrp,png_ptr), ptr);
    }

    /* Reset the CRC variable to 32 bits of 1's.  Care must be taken
     * in case CRC is > 32 bits to leave the top bits 0.
     */
    void /* PRIVATE */
    png_reset_crc(png_structrp png_ptr)
    {
       /* The cast is safe because the crc is a 32 bit value. */
       png_ptr->crc = (png_uint_32)crc32(0, Z_NULL, 0);
    }

    /* Calculate the CRC over a section of data.  We can only pass as
     * much data to this routine as the largest single buffer size.  We
     * also check that this data will actually be used before going to the
     * trouble of calculating it.
     */
    void /* PRIVATE */
    png_calculate_crc(png_structrp png_ptr, png_const_bytep ptr, png_size_t length)
    {
       int need_crc = 1;

       if (PNG_CHUNK_ANCILLARY(png_ptr->chunk_name))
       {
          if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_MASK) ==
              (PNG_FLAG_CRC_ANCILLARY_USE | PNG_FLAG_CRC_ANCILLARY_NOWARN))
             need_crc = 0;
       }

       else /* critical */
       {
          if (png_ptr->flags & PNG_FLAG_CRC_CRITICAL_IGNORE)
             need_crc = 0;
       }

       /* 'uLong' is defined in zlib.h as unsigned long; this means that on some
        * systems it is a 64 bit value.  crc32, however, returns 32 bits so the
        * following cast is safe.  'uInt' may be no more than 16 bits, so it is
        * necessary to perform a loop here.
        */
       if (need_crc && length > 0)
       {
          uLong crc = png_ptr->crc; /* Should never issue a warning */

          do
          {
             uInt safe_length = (uInt)length;
             if (safe_length == 0)
                safe_length = (uInt)-1; /* evil, but safe */

             crc = crc32(crc, ptr, safe_length);

             /* The following should never issue compiler warnings; if they do the
              * target system has characteristics that will probably violate other
              * assumptions within the libpng code.
              */
             ptr += safe_length;
             length -= safe_length;
          }
          while (length > 0);

          /* And the following is always safe because the crc is only 32 bits. */
          png_ptr->crc = (png_uint_32)crc;
       }
    }

    /* Check a user supplied version number, called from both read and write
     * functions that create a png_struct.
     */
    int
    png_user_version_check(png_structrp png_ptr, png_const_charp user_png_ver)
    {
       if (user_png_ver)
       {
          int i = 0;

          do
          {
             if (user_png_ver[i] != png_libpng_ver[i])
                png_ptr->flags |= PNG_FLAG_LIBRARY_MISMATCH;
          } while (png_libpng_ver[i++]);
       }

       else
          png_ptr->flags |= PNG_FLAG_LIBRARY_MISMATCH;

       if (png_ptr->flags & PNG_FLAG_LIBRARY_MISMATCH)
       {
         /* Libpng 0.90 and later are binary incompatible with libpng 0.89, so
          * we must recompile any applications that use any older library version.
          * For versions after libpng 1.0, we will be compatible, so we need
          * only check the first and third digits (note that when we reach version
          * 1.10 we will need to check the fourth symbol, namely user_png_ver[3]).
          */
          if (user_png_ver == NULL || user_png_ver[0] != png_libpng_ver[0] ||
              (user_png_ver[0] == '1' && (user_png_ver[2] != png_libpng_ver[2] ||
              user_png_ver[3] != png_libpng_ver[3])) ||
              (user_png_ver[0] == '0' && user_png_ver[2] < '9'))
          {
    #ifdef PNG_WARNINGS_SUPPORTED
             size_t pos = 0;
             char m[128];

             pos = png_safecat(m, (sizeof m), pos,
                 "Application built with libpng-");
             pos = png_safecat(m, (sizeof m), pos, user_png_ver);
             pos = png_safecat(m, (sizeof m), pos, " but running with ");
             pos = png_safecat(m, (sizeof m), pos, png_libpng_ver);

             png_warning(png_ptr, m);
    #endif

    #ifdef PNG_ERROR_NUMBERS_SUPPORTED
             png_ptr->flags = 0;
    #endif

             return 0;
          }
       }

       /* Success return. */
       return 1;
    }

    /* Generic function to create a png_struct for either read or write - this
     * contains the common initialization.
     */
    PNG_FUNCTION(png_structp /* PRIVATE */,
    png_create_png_struct,(png_const_charp user_png_ver, png_voidp error_ptr,
        png_error_ptr error_fn, png_error_ptr warn_fn, png_voidp mem_ptr,
        png_malloc_ptr malloc_fn, png_free_ptr free_fn),PNG_ALLOCATED)
    {
       png_struct create_struct;
    #  ifdef PNG_SETJMP_SUPPORTED
          jmp_buf create_jmp_buf;
    #  endif

       /* This temporary stack-allocated structure is used to provide a place to
        * build enough context to allow the user provided memory allocator (if any)
        * to be called.
        */
       memset(&create_struct, 0, (sizeof create_struct));

       /* Added at libpng-1.2.6 */
    #  ifdef PNG_USER_LIMITS_SUPPORTED
          create_struct.user_width_max = PNG_USER_WIDTH_MAX;
          create_struct.user_height_max = PNG_USER_HEIGHT_MAX;

    #     ifdef PNG_USER_CHUNK_CACHE_MAX
             /* Added at libpng-1.2.43 and 1.4.0 */
             create_struct.user_chunk_cache_max = PNG_USER_CHUNK_CACHE_MAX;
    #     endif

    #     ifdef PNG_USER_CHUNK_MALLOC_MAX
             /* Added at libpng-1.2.43 and 1.4.1, required only for read but exists
              * in png_struct regardless.
              */
             create_struct.user_chunk_malloc_max = PNG_USER_CHUNK_MALLOC_MAX;
    #     endif
    #  endif

       /* The following two API calls simply set fields in png_struct, so it is safe
        * to do them now even though error handling is not yet set up.
        */
    #  ifdef PNG_USER_MEM_SUPPORTED
          png_set_mem_fn(&create_struct, mem_ptr, malloc_fn, free_fn);
    #  endif

       /* (*error_fn) can return control to the caller after the error_ptr is set,
        * this will result in a memory leak unless the error_fn does something
        * extremely sophisticated.  The design lacks merit but is implicit in the
        * API.
        */
       png_set_error_fn(&create_struct, error_ptr, error_fn, warn_fn);

    #  ifdef PNG_SETJMP_SUPPORTED
          if (!setjmp(create_jmp_buf))
          {
             /* Temporarily fake out the longjmp information until we have
              * successfully completed this function.  This only works if we have
              * setjmp() support compiled in, but it is safe - this stuff should
              * never happen.
              */
             create_struct.jmp_buf_ptr = &create_jmp_buf;
             create_struct.jmp_buf_size = 0; /*stack allocation*/
             create_struct.longjmp_fn = longjmp;
    #  else
          {
    #  endif
             /* Call the general version checker (shared with read and write code):
              */
             if (png_user_version_check(&create_struct, user_png_ver))
             {
                png_structrp png_ptr = png_voidcast(png_structrp,
                   png_malloc_warn(&create_struct, (sizeof *png_ptr)));

                if (png_ptr != NULL)
                {
                   /* png_ptr->zstream holds a back-pointer to the png_struct, so
                    * this can only be done now:
                    */
                   create_struct.zstream.zalloc = png_zalloc;
                   create_struct.zstream.zfree = png_zfree;
                   create_struct.zstream.opaque = png_ptr;

    #              ifdef PNG_SETJMP_SUPPORTED
                      /* Eliminate the local error handling: */
                      create_struct.jmp_buf_ptr = NULL;
                      create_struct.jmp_buf_size = 0;
                      create_struct.longjmp_fn = 0;
    #              endif

                   *png_ptr = create_struct;

                   /* This is the successful return point */
                   return png_ptr;
                }
             }
          }

       /* A longjmp because of a bug in the application storage allocator or a
        * simple failure to allocate the png_struct.
        */
       return NULL;
    }

    /* Allocate the memory for an info_struct for the application. */
    PNG_FUNCTION(png_infop,PNGAPI
    png_create_info_struct,(png_const_structrp png_ptr),PNG_ALLOCATED)
    {
       png_inforp info_ptr;

       png_debug(1, "in png_create_info_struct");

       if (png_ptr == NULL)
          return NULL;

       /* Use the internal API that does not (or at least should not) error out, so
        * that this call always returns ok.  The application typically sets up the
        * error handling *after* creating the info_struct because this is the way it
        * has always been done in 'example.c'.
        */
       info_ptr = png_voidcast(png_inforp, png_malloc_base(png_ptr,
          (sizeof *info_ptr)));

       if (info_ptr != NULL)
          memset(info_ptr, 0, (sizeof *info_ptr));

       return info_ptr;
    }

    /* This function frees the memory associated with a single info struct.
     * Normally, one would use either png_destroy_read_struct() or
     * png_destroy_write_struct() to free an info struct, but this may be
     * useful for some applications.  From libpng 1.6.0 this function is also used
     * internally to implement the png_info release part of the 'struct' destroy
     * APIs.  This ensures that all possible approaches free the same data (all of
     * it).
     */
    void PNGAPI
    png_destroy_info_struct(png_const_structrp png_ptr, png_infopp info_ptr_ptr)
    {
       png_inforp info_ptr = NULL;

       png_debug(1, "in png_destroy_info_struct");

       if (png_ptr == NULL)
          return;

       if (info_ptr_ptr != NULL)
          info_ptr = *info_ptr_ptr;

       if (info_ptr != NULL)
       {
          /* Do this first in case of an error below; if the app implements its own
           * memory management this can lead to png_free calling png_error, which
           * will abort this routine and return control to the app error handler.
           * An infinite loop may result if it then tries to free the same info
           * ptr.
           */
          *info_ptr_ptr = NULL;

          png_free_data(png_ptr, info_ptr, PNG_FREE_ALL, -1);
          memset(info_ptr, 0, (sizeof *info_ptr));
          png_free(png_ptr, info_ptr);
       }
    }

    /* Initialize the info structure.  This is now an internal function (0.89)
     * and applications using it are urged to use png_create_info_struct()
     * instead.  Use deprecated in 1.6.0, internal use removed (used internally it
     * is just a memset).
     *
     * NOTE: it is almost inconceivable that this API is used because it bypasses
     * the user-memory mechanism and the user error handling/warning mechanisms in
     * those cases where it does anything other than a memset.
     */
    PNG_FUNCTION(void,PNGAPI
    png_info_init_3,(png_infopp ptr_ptr, png_size_t png_info_struct_size),
       PNG_DEPRECATED)
    {
       png_inforp info_ptr = *ptr_ptr;

       png_debug(1, "in png_info_init_3");

       if (info_ptr == NULL)
          return;

       if ((sizeof (png_info)) > png_info_struct_size)
       {
          *ptr_ptr = NULL;
          /* The following line is why this API should not be used: */
          free(info_ptr);
          info_ptr = png_voidcast(png_inforp, png_malloc_base(NULL,
             (sizeof *info_ptr)));
          *ptr_ptr = info_ptr;
       }

       /* Set everything to 0 */
       memset(info_ptr, 0, (sizeof *info_ptr));
    }

    /* The following API is not called internally */
    void PNGAPI
    png_data_freer(png_const_structrp png_ptr, png_inforp info_ptr,
       int freer, png_uint_32 mask)
    {
       png_debug(1, "in png_data_freer");

       if (png_ptr == NULL || info_ptr == NULL)
          return;

       if (freer == PNG_DESTROY_WILL_FREE_DATA)
          info_ptr->free_me |= mask;

       else if (freer == PNG_USER_WILL_FREE_DATA)
          info_ptr->free_me &= ~mask;

       else
          png_error(png_ptr, "Unknown freer parameter in png_data_freer");
    }

    void PNGAPI
    png_free_data(png_const_structrp png_ptr, png_inforp info_ptr, png_uint_32 mask,
       int num)
    {
       png_debug(1, "in png_free_data");

       if (png_ptr == NULL || info_ptr == NULL)
          return;

    #ifdef PNG_TEXT_SUPPORTED
       /* Free text item num or (if num == -1) all text items */
       if ((mask & PNG_FREE_TEXT) & info_ptr->free_me)
       {
          if (num != -1)
          {
             if (info_ptr->text && info_ptr->text[num].key)
             {
                png_free(png_ptr, info_ptr->text[num].key);
                info_ptr->text[num].key = NULL;
             }
          }

          else
          {
             int i;
             for (i = 0; i < info_ptr->num_text; i++)
                 png_free_data(png_ptr, info_ptr, PNG_FREE_TEXT, i);
             png_free(png_ptr, info_ptr->text);
             info_ptr->text = NULL;
             info_ptr->num_text=0;
          }
       }
    #endif

    #ifdef PNG_tRNS_SUPPORTED
       /* Free any tRNS entry */
       if ((mask & PNG_FREE_TRNS) & info_ptr->free_me)
       {
          png_free(png_ptr, info_ptr->trans_alpha);
          info_ptr->trans_alpha = NULL;
          info_ptr->valid &= ~PNG_INFO_tRNS;
       }
    #endif

    #ifdef PNG_sCAL_SUPPORTED
       /* Free any sCAL entry */
       if ((mask & PNG_FREE_SCAL) & info_ptr->free_me)
       {
          png_free(png_ptr, info_ptr->scal_s_width);
          png_free(png_ptr, info_ptr->scal_s_height);
          info_ptr->scal_s_width = NULL;
          info_ptr->scal_s_height = NULL;
          info_ptr->valid &= ~PNG_INFO_sCAL;
       }
    #endif

    #ifdef PNG_pCAL_SUPPORTED
       /* Free any pCAL entry */
       if ((mask & PNG_FREE_PCAL) & info_ptr->free_me)
       {
          png_free(png_ptr, info_ptr->pcal_purpose);
          png_free(png_ptr, info_ptr->pcal_units);
          info_ptr->pcal_purpose = NULL;
          info_ptr->pcal_units = NULL;
          if (info_ptr->pcal_params != NULL)
             {
                unsigned int i;
                for (i = 0; i < info_ptr->pcal_nparams; i++)
                {
                   png_free(png_ptr, info_ptr->pcal_params[i]);
                   info_ptr->pcal_params[i] = NULL;
                }
                png_free(png_ptr, info_ptr->pcal_params);
                info_ptr->pcal_params = NULL;
             }
          info_ptr->valid &= ~PNG_INFO_pCAL;
       }
    #endif

    #ifdef PNG_iCCP_SUPPORTED
       /* Free any profile entry */
       if ((mask & PNG_FREE_ICCP) & info_ptr->free_me)
       {
          png_free(png_ptr, info_ptr->iccp_name);
          png_free(png_ptr, info_ptr->iccp_profile);
          info_ptr->iccp_name = NULL;
          info_ptr->iccp_profile = NULL;
          info_ptr->valid &= ~PNG_INFO_iCCP;
       }
    #endif

    #ifdef PNG_sPLT_SUPPORTED
       /* Free a given sPLT entry, or (if num == -1) all sPLT entries */
       if ((mask & PNG_FREE_SPLT) & info_ptr->free_me)
       {
          if (num != -1)
          {
             if (info_ptr->splt_palettes)
             {
                png_free(png_ptr, info_ptr->splt_palettes[num].name);
                png_free(png_ptr, info_ptr->splt_palettes[num].entries);
                info_ptr->splt_palettes[num].name = NULL;
                info_ptr->splt_palettes[num].entries = NULL;
             }
          }

          else
          {
             if (info_ptr->splt_palettes_num)
             {
                int i;
                for (i = 0; i < info_ptr->splt_palettes_num; i++)
                   png_free_data(png_ptr, info_ptr, PNG_FREE_SPLT, (int)i);

                png_free(png_ptr, info_ptr->splt_palettes);
                info_ptr->splt_palettes = NULL;
                info_ptr->splt_palettes_num = 0;
             }
             info_ptr->valid &= ~PNG_INFO_sPLT;
          }
       }
    #endif

    #ifdef PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED
       if ((mask & PNG_FREE_UNKN) & info_ptr->free_me)
       {
          if (num != -1)
          {
              if (info_ptr->unknown_chunks)
              {
                 png_free(png_ptr, info_ptr->unknown_chunks[num].data);
                 info_ptr->unknown_chunks[num].data = NULL;
              }
          }

          else
          {
             int i;

             if (info_ptr->unknown_chunks_num)
             {
                for (i = 0; i < info_ptr->unknown_chunks_num; i++)
                   png_free_data(png_ptr, info_ptr, PNG_FREE_UNKN, (int)i);

                png_free(png_ptr, info_ptr->unknown_chunks);
                info_ptr->unknown_chunks = NULL;
                info_ptr->unknown_chunks_num = 0;
             }
          }
       }
    #endif

    #ifdef PNG_hIST_SUPPORTED
       /* Free any hIST entry */
       if ((mask & PNG_FREE_HIST)  & info_ptr->free_me)
       {
          png_free(png_ptr, info_ptr->hist);
          info_ptr->hist = NULL;
          info_ptr->valid &= ~PNG_INFO_hIST;
       }
    #endif

       /* Free any PLTE entry that was internally allocated */
       if ((mask & PNG_FREE_PLTE) & info_ptr->free_me)
       {
          png_free(png_ptr, info_ptr->palette);
          info_ptr->palette = NULL;
          info_ptr->valid &= ~PNG_INFO_PLTE;
          info_ptr->num_palette = 0;
       }

    #ifdef PNG_INFO_IMAGE_SUPPORTED
       /* Free any image bits attached to the info structure */
       if ((mask & PNG_FREE_ROWS) & info_ptr->free_me)
       {
          if (info_ptr->row_pointers)
          {
             png_uint_32 row;
             for (row = 0; row < info_ptr->height; row++)
             {
                png_free(png_ptr, info_ptr->row_pointers[row]);
                info_ptr->row_pointers[row] = NULL;
             }
             png_free(png_ptr, info_ptr->row_pointers);
             info_ptr->row_pointers = NULL;
          }
          info_ptr->valid &= ~PNG_INFO_IDAT;
       }
    #endif

       if (num != -1)
          mask &= ~PNG_FREE_MUL;

       info_ptr->free_me &= ~mask;
    }
    #endif /* defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) */

    /* This function returns a pointer to the io_ptr associated with the user
     * functions.  The application should free any memory associated with this
     * pointer before png_write_destroy() or png_read_destroy() are called.
     */
    png_voidp PNGAPI
    png_get_io_ptr(png_const_structrp png_ptr)
    {
       if (png_ptr == NULL)
          return (NULL);

       return (png_ptr->io_ptr);
    }

    #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
    #  ifdef PNG_STDIO_SUPPORTED
    /* Initialize the default input/output functions for the PNG file.  If you
     * use your own read or write routines, you can call either png_set_read_fn()
     * or png_set_write_fn() instead of png_init_io().  If you have defined
     * PNG_NO_STDIO or otherwise disabled PNG_STDIO_SUPPORTED, you must use a
     * function of your own because "FILE *" isn't necessarily available.
     */
    void PNGAPI
    png_init_io(png_structrp png_ptr, png_FILE_p fp)
    {
       png_debug(1, "in png_init_io");

       if (png_ptr == NULL)
          return;

       png_ptr->io_ptr = (png_voidp)fp;
    }
    #  endif

    #ifdef PNG_SAVE_INT_32_SUPPORTED
    /* The png_save_int_32 function assumes integers are stored in two's
     * complement format.  If this isn't the case, then this routine needs to
     * be modified to write data in two's complement format.  Note that,
     * the following works correctly even if png_int_32 has more than 32 bits
     * (compare the more complex code required on read for sign extension.)
     */
    void PNGAPI
    png_save_int_32(png_bytep buf, png_int_32 i)
    {
       buf[0] = (png_byte)((i >> 24) & 0xff);
       buf[1] = (png_byte)((i >> 16) & 0xff);
       buf[2] = (png_byte)((i >> 8) & 0xff);
       buf[3] = (png_byte)(i & 0xff);
    }
    #endif

    #  ifdef PNG_TIME_RFC1123_SUPPORTED
    /* Convert the supplied time into an RFC 1123 string suitable for use in
     * a "Creation Time" or other text-based time string.
     */
    int PNGAPI
    png_convert_to_rfc1123_buffer(char out[29], png_const_timep ptime)
    {
       static PNG_CONST char short_months[12][4] =
            {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
             "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};

       if (out == NULL)
          return 0;

       if (ptime->year > 9999 /* RFC1123 limitation */ ||
           ptime->month == 0    ||  ptime->month > 12  ||
           ptime->day   == 0    ||  ptime->day   > 31  ||
           ptime->hour  > 23    ||  ptime->minute > 59 ||
           ptime->second > 60)
          return 0;

       {
          size_t pos = 0;
          char number_buf[5]; /* enough for a four-digit year */

    #     define APPEND_STRING(string) pos = png_safecat(out, 29, pos, (string))
    #     define APPEND_NUMBER(format, value)\
             APPEND_STRING(PNG_FORMAT_NUMBER(number_buf, format, (value)))
    #     define APPEND(ch) if (pos < 28) out[pos++] = (ch)

          APPEND_NUMBER(PNG_NUMBER_FORMAT_u, (unsigned)ptime->day);
          APPEND(' ');
          APPEND_STRING(short_months[(ptime->month - 1)]);
          APPEND(' ');
          APPEND_NUMBER(PNG_NUMBER_FORMAT_u, ptime->year);
          APPEND(' ');
          APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->hour);
          APPEND(':');
          APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->minute);
          APPEND(':');
          APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->second);
          APPEND_STRING(" +0000"); /* This reliably terminates the buffer */

    #     undef APPEND
    #     undef APPEND_NUMBER
    #     undef APPEND_STRING
       }

       return 1;
    }

    #     if PNG_LIBPNG_VER < 10700
    /* To do: remove the following from libpng-1.7 */
    /* Original API that uses a private buffer in png_struct.
     * Deprecated because it causes png_struct to carry a spurious temporary
     * buffer (png_struct::time_buffer), better to have the caller pass this in.
     */
    png_const_charp PNGAPI
    png_convert_to_rfc1123(png_structrp png_ptr, png_const_timep ptime)
    {
       if (png_ptr != NULL)
       {
          /* The only failure above if png_ptr != NULL is from an invalid ptime */
          if (!png_convert_to_rfc1123_buffer(png_ptr->time_buffer, ptime))
             png_warning(png_ptr, "Ignoring invalid time value");

          else
             return png_ptr->time_buffer;
       }

       return NULL;
    }
    #     endif
    #  endif /* PNG_TIME_RFC1123_SUPPORTED */

    #endif /* defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) */

    png_const_charp PNGAPI
    png_get_copyright(png_const_structrp png_ptr)
    {
       PNG_UNUSED(png_ptr)  /* Silence compiler warning about unused png_ptr */
    #ifdef PNG_STRING_COPYRIGHT
       return PNG_STRING_COPYRIGHT
    #else
    #  ifdef __STDC__
       return PNG_STRING_NEWLINE \
         "libpng version 1.6.7 - November 14, 2013" PNG_STRING_NEWLINE \
         "Copyright (c) 1998-2013 Glenn Randers-Pehrson" PNG_STRING_NEWLINE \
         "Copyright (c) 1996-1997 Andreas Dilger" PNG_STRING_NEWLINE \
         "Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc." \
         PNG_STRING_NEWLINE;
    #  else
          return "libpng version 1.6.7 - November 14, 2013\
          Copyright (c) 1998-2013 Glenn Randers-Pehrson\
          Copyright (c) 1996-1997 Andreas Dilger\
          Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.";
    #  endif
    #endif
    }

    /* The following return the library version as a short string in the
     * format 1.0.0 through 99.99.99zz.  To get the version of *.h files
     * used with your application, print out PNG_LIBPNG_VER_STRING, which
     * is defined in png.h.
     * Note: now there is no difference between png_get_libpng_ver() and
     * png_get_header_ver().  Due to the version_nn_nn_nn typedef guard,
     * it is guaranteed that png.c uses the correct version of png.h.
     */
    png_const_charp PNGAPI
    png_get_libpng_ver(png_const_structrp png_ptr)
    {
       /* Version of *.c files used when building libpng */
       return png_get_header_ver(png_ptr);
    }

    png_const_charp PNGAPI
    png_get_header_ver(png_const_structrp png_ptr)
    {
       /* Version of *.h files used when building libpng */
       PNG_UNUSED(png_ptr)  /* Silence compiler warning about unused png_ptr */
       return PNG_LIBPNG_VER_STRING;
    }

    png_const_charp PNGAPI
    png_get_header_version(png_const_structrp png_ptr)
    {
       /* Returns longer string containing both version and date */
       PNG_UNUSED(png_ptr)  /* Silence compiler warning about unused png_ptr */
    #ifdef __STDC__
       return PNG_HEADER_VERSION_STRING
    #  ifndef PNG_READ_SUPPORTED
       "     (NO READ SUPPORT)"
    #  endif
       PNG_STRING_NEWLINE;
    #else
       return PNG_HEADER_VERSION_STRING;
    #endif
    }

    #ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
    int PNGAPI
    png_handle_as_unknown(png_const_structrp png_ptr, png_const_bytep chunk_name)
    {
       /* Check chunk_name and return "keep" value if it's on the list, else 0 */
       png_const_bytep p, p_end;

       if (png_ptr == NULL || chunk_name == NULL || png_ptr->num_chunk_list == 0)
          return PNG_HANDLE_CHUNK_AS_DEFAULT;

       p_end = png_ptr->chunk_list;
       p = p_end + png_ptr->num_chunk_list*5; /* beyond end */

       /* The code is the fifth byte after each four byte string.  Historically this
        * code was always searched from the end of the list, this is no longer
        * necessary because the 'set' routine handles duplicate entries correcty.
        */
       do /* num_chunk_list > 0, so at least one */
       {
          p -= 5;

          if (!memcmp(chunk_name, p, 4))
             return p[4];
       }
       while (p > p_end);

       /* This means that known chunks should be processed and unknown chunks should
        * be handled according to the value of png_ptr->unknown_default; this can be
        * confusing because, as a result, there are two levels of defaulting for
        * unknown chunks.
        */
       return PNG_HANDLE_CHUNK_AS_DEFAULT;
    }

    #if defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED) ||\
       defined(PNG_HANDLE_AS_UNKNOWN_SUPPORTED)
    int /* PRIVATE */
    png_chunk_unknown_handling(png_const_structrp png_ptr, png_uint_32 chunk_name)
    {
       png_byte chunk_string[5];

       PNG_CSTRING_FROM_CHUNK(chunk_string, chunk_name);
       return png_handle_as_unknown(png_ptr, chunk_string);
    }
    #endif /* READ_UNKNOWN_CHUNKS || HANDLE_AS_UNKNOWN */
    #endif /* SET_UNKNOWN_CHUNKS */

    #ifdef PNG_READ_SUPPORTED
    /* This function, added to libpng-1.0.6g, is untested. */
    int PNGAPI
    png_reset_zstream(png_structrp png_ptr)
    {
       if (png_ptr == NULL)
          return Z_STREAM_ERROR;

       /* WARNING: this resets the window bits to the maximum! */
       return (inflateReset(&png_ptr->zstream));
    }
    #endif /* PNG_READ_SUPPORTED */

    /* This function was added to libpng-1.0.7 */
    png_uint_32 PNGAPI
    png_access_version_number(void)
    {
       /* Version of *.c files used when building libpng */
       return((png_uint_32)PNG_LIBPNG_VER);
    }

    #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
    /* Ensure that png_ptr->zstream.msg holds some appropriate error message string.
     * If it doesn't 'ret' is used to set it to something appropriate, even in cases
     * like Z_OK or Z_STREAM_END where the error code is apparently a success code.
     */
    void /* PRIVATE */
    png_zstream_error(png_structrp png_ptr, int ret)
    {
       /* Translate 'ret' into an appropriate error string, priority is given to the
        * one in zstream if set.  This always returns a string, even in cases like
        * Z_OK or Z_STREAM_END where the error code is a success code.
        */
       if (png_ptr->zstream.msg == NULL) switch (ret)
       {
          default:
          case Z_OK:
             png_ptr->zstream.msg = PNGZ_MSG_CAST("unexpected zlib return code");
             break;

          case Z_STREAM_END:
             /* Normal exit */
             png_ptr->zstream.msg = PNGZ_MSG_CAST("unexpected end of LZ stream");
             break;

          case Z_NEED_DICT:
             /* This means the deflate stream did not have a dictionary; this
              * indicates a bogus PNG.
              */
             png_ptr->zstream.msg = PNGZ_MSG_CAST("missing LZ dictionary");
             break;

          case Z_ERRNO:
             /* gz APIs only: should not happen */
             png_ptr->zstream.msg = PNGZ_MSG_CAST("zlib IO error");
             break;

          case Z_STREAM_ERROR:
             /* internal libpng error */
             png_ptr->zstream.msg = PNGZ_MSG_CAST("bad parameters to zlib");
             break;

          case Z_DATA_ERROR:
             png_ptr->zstream.msg = PNGZ_MSG_CAST("damaged LZ stream");
             break;

          case Z_MEM_ERROR:
             png_ptr->zstream.msg = PNGZ_MSG_CAST("insufficient memory");
             break;

          case Z_BUF_ERROR:
             /* End of input or output; not a problem if the caller is doing
              * incremental read or write.
              */
             png_ptr->zstream.msg = PNGZ_MSG_CAST("truncated");
             break;

          case Z_VERSION_ERROR:
             png_ptr->zstream.msg = PNGZ_MSG_CAST("unsupported zlib version");
             break;

          case PNG_UNEXPECTED_ZLIB_RETURN:
             /* Compile errors here mean that zlib now uses the value co-opted in
              * pngpriv.h for PNG_UNEXPECTED_ZLIB_RETURN; update the switch above
              * and change pngpriv.h.  Note that this message is "... return",
              * whereas the default/Z_OK one is "... return code".
              */
             png_ptr->zstream.msg = PNGZ_MSG_CAST("unexpected zlib return");
             break;
       }
    }

    /* png_convert_size: a PNGAPI but no longer in png.h, so deleted
     * at libpng 1.5.5!
     */

    /* Added at libpng version 1.2.34 and 1.4.0 (moved from pngset.c) */
    #ifdef PNG_GAMMA_SUPPORTED /* always set if COLORSPACE */
    static int
    png_colorspace_check_gamma(png_const_structrp png_ptr,
       png_colorspacerp colorspace, png_fixed_point gAMA, int from)
       /* This is called to check a new gamma value against an existing one.  The
        * routine returns false if the new gamma value should not be written.
        *
        * 'from' says where the new gamma value comes from:
        *
        *    0: the new gamma value is the libpng estimate for an ICC profile
        *    1: the new gamma value comes from a gAMA chunk
        *    2: the new gamma value comes from an sRGB chunk
        */
    {
       png_fixed_point gtest;

       if ((colorspace->flags & PNG_COLORSPACE_HAVE_GAMMA) != 0 &&
          (!png_muldiv(&gtest, colorspace->gamma, PNG_FP_1, gAMA) ||
          png_gamma_significant(gtest)))
       {
          /* Either this is an sRGB image, in which case the calculated gamma
           * approximation should match, or this is an image with a profile and the
           * value libpng calculates for the gamma of the profile does not match the
           * value recorded in the file.  The former, sRGB, case is an error, the
           * latter is just a warning.
           */
          if ((colorspace->flags & PNG_COLORSPACE_FROM_sRGB) != 0 || from == 2)
          {
             png_chunk_report(png_ptr, "gamma value does not match sRGB",
                PNG_CHUNK_ERROR);
             /* Do not overwrite an sRGB value */
             return from == 2;
          }

          else /* sRGB tag not involved */
          {
             png_chunk_report(png_ptr, "gamma value does not match libpng estimate",
                PNG_CHUNK_WARNING);
             return from == 1;
          }
       }

       return 1;
    }

    void /* PRIVATE */
    png_colorspace_set_gamma(png_const_structrp png_ptr,
       png_colorspacerp colorspace, png_fixed_point gAMA)
    {
       /* Changed in libpng-1.5.4 to limit the values to ensure overflow can't
        * occur.  Since the fixed point representation is assymetrical it is
        * possible for 1/gamma to overflow the limit of 21474 and this means the
        * gamma value must be at least 5/100000 and hence at most 20000.0.  For
        * safety the limits here are a little narrower.  The values are 0.00016 to
        * 6250.0, which are truly ridiculous gamma values (and will produce
        * displays that are all black or all white.)
        *
        * In 1.6.0 this test replaces the ones in pngrutil.c, in the gAMA chunk
        * handling code, which only required the value to be >0.
        */
       png_const_charp errmsg;

       if (gAMA < 16 || gAMA > 625000000)
          errmsg = "gamma value out of range";

    #  ifdef PNG_READ_gAMA_SUPPORTED
          /* Allow the application to set the gamma value more than once */
          else if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0 &&
             (colorspace->flags & PNG_COLORSPACE_FROM_gAMA) != 0)
             errmsg = "duplicate";
    #  endif

       /* Do nothing if the colorspace is already invalid */
       else if (colorspace->flags & PNG_COLORSPACE_INVALID)
          return;

       else
       {
          if (png_colorspace_check_gamma(png_ptr, colorspace, gAMA, 1/*from gAMA*/))
          {
             /* Store this gamma value. */
             colorspace->gamma = gAMA;
             colorspace->flags |=
                (PNG_COLORSPACE_HAVE_GAMMA | PNG_COLORSPACE_FROM_gAMA);
          }

          /* At present if the check_gamma test fails the gamma of the colorspace is
           * not updated however the colorspace is not invalidated.  This
           * corresponds to the case where the existing gamma comes from an sRGB
           * chunk or profile.  An error message has already been output.
           */
          return;
       }

       /* Error exit - errmsg has been set. */
       colorspace->flags |= PNG_COLORSPACE_INVALID;
       png_chunk_report(png_ptr, errmsg, PNG_CHUNK_WRITE_ERROR);
    }

    void /* PRIVATE */
    png_colorspace_sync_info(png_const_structrp png_ptr, png_inforp info_ptr)
    {
       if (info_ptr->colorspace.flags & PNG_COLORSPACE_INVALID)
       {
          /* Everything is invalid */
          info_ptr->valid &= ~(PNG_INFO_gAMA|PNG_INFO_cHRM|PNG_INFO_sRGB|
             PNG_INFO_iCCP);

    #     ifdef PNG_COLORSPACE_SUPPORTED
             /* Clean up the iCCP profile now if it won't be used. */
             png_free_data(png_ptr, info_ptr, PNG_FREE_ICCP, -1/*not used*/);
    #     else
             PNG_UNUSED(png_ptr)
    #     endif
       }

       else
       {
    #     ifdef PNG_COLORSPACE_SUPPORTED
             /* Leave the INFO_iCCP flag set if the pngset.c code has already set
              * it; this allows a PNG to contain a profile which matches sRGB and
              * yet still have that profile retrievable by the application.
              */
             if (info_ptr->colorspace.flags & PNG_COLORSPACE_MATCHES_sRGB)
                info_ptr->valid |= PNG_INFO_sRGB;

             else
                info_ptr->valid &= ~PNG_INFO_sRGB;

             if (info_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_ENDPOINTS)
                info_ptr->valid |= PNG_INFO_cHRM;

             else
                info_ptr->valid &= ~PNG_INFO_cHRM;
    #     endif

          if (info_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_GAMMA)
             info_ptr->valid |= PNG_INFO_gAMA;

          else
             info_ptr->valid &= ~PNG_INFO_gAMA;
       }
    }

    #ifdef PNG_READ_SUPPORTED
    void /* PRIVATE */
    png_colorspace_sync(png_const_structrp png_ptr, png_inforp info_ptr)
    {
       if (info_ptr == NULL) /* reduce code size; check here not in the caller */
          return;

       info_ptr->colorspace = png_ptr->colorspace;
       png_colorspace_sync_info(png_ptr, info_ptr);
    }
    #endif
    #endif

    #ifdef PNG_COLORSPACE_SUPPORTED
    /* Added at libpng-1.5.5 to support read and write of true CIEXYZ values for
     * cHRM, as opposed to using chromaticities.  These internal APIs return
     * non-zero on a parameter error.  The X, Y and Z values are required to be
     * positive and less than 1.0.
     */
    static int
    png_xy_from_XYZ(png_xy *xy, const png_XYZ *XYZ)
    {
       png_int_32 d, dwhite, whiteX, whiteY;

       d = XYZ->red_X + XYZ->red_Y + XYZ->red_Z;
       if (!png_muldiv(&xy->redx, XYZ->red_X, PNG_FP_1, d)) return 1;
       if (!png_muldiv(&xy->redy, XYZ->red_Y, PNG_FP_1, d)) return 1;
       dwhite = d;
       whiteX = XYZ->red_X;
       whiteY = XYZ->red_Y;

       d = XYZ->green_X + XYZ->green_Y + XYZ->green_Z;
       if (!png_muldiv(&xy->greenx, XYZ->green_X, PNG_FP_1, d)) return 1;
       if (!png_muldiv(&xy->greeny, XYZ->green_Y, PNG_FP_1, d)) return 1;
       dwhite += d;
       whiteX += XYZ->green_X;
       whiteY += XYZ->green_Y;

       d = XYZ->blue_X + XYZ->blue_Y + XYZ->blue_Z;
       if (!png_muldiv(&xy->bluex, XYZ->blue_X, PNG_FP_1, d)) return 1;
       if (!png_muldiv(&xy->bluey, XYZ->blue_Y, PNG_FP_1, d)) return 1;
       dwhite += d;
       whiteX += XYZ->blue_X;
       whiteY += XYZ->blue_Y;

       /* The reference white is simply the sum of the end-point (X,Y,Z) vectors,
        * thus:
        */
       if (!png_muldiv(&xy->whitex, whiteX, PNG_FP_1, dwhite)) return 1;
       if (!png_muldiv(&xy->whitey, whiteY, PNG_FP_1, dwhite)) return 1;

       return 0;
    }

    static int
    png_XYZ_from_xy(png_XYZ *XYZ, const png_xy *xy)
    {
       png_fixed_point red_inverse, green_inverse, blue_scale;
       png_fixed_point left, right, denominator;

       /* Check xy and, implicitly, z.  Note that wide gamut color spaces typically
        * have end points with 0 tristimulus values (these are impossible end
        * points, but they are used to cover the possible colors.)
        */
       if (xy->redx < 0 || xy->redx > PNG_FP_1) return 1;
       if (xy->redy < 0 || xy->redy > PNG_FP_1-xy->redx) return 1;
       if (xy->greenx < 0 || xy->greenx > PNG_FP_1) return 1;
       if (xy->greeny < 0 || xy->greeny > PNG_FP_1-xy->greenx) return 1;
       if (xy->bluex < 0 || xy->bluex > PNG_FP_1) return 1;
       if (xy->bluey < 0 || xy->bluey > PNG_FP_1-xy->bluex) return 1;
       if (xy->whitex < 0 || xy->whitex > PNG_FP_1) return 1;
       if (xy->whitey < 0 || xy->whitey > PNG_FP_1-xy->whitex) return 1;

       /* The reverse calculation is more difficult because the original tristimulus
        * value had 9 independent values (red,green,blue)x(X,Y,Z) however only 8
        * derived values were recorded in the cHRM chunk;
        * (red,green,blue,white)x(x,y).  This loses one degree of freedom and
        * therefore an arbitrary ninth value has to be introduced to undo the
        * original transformations.
        *
        * Think of the original end-points as points in (X,Y,Z) space.  The
        * chromaticity values (c) have the property:
        *
        *           C
        *   c = ---------
        *       X + Y + Z
        *
        * For each c (x,y,z) from the corresponding original C (X,Y,Z).  Thus the
        * three chromaticity values (x,y,z) for each end-point obey the
        * relationship:
        *
        *   x + y + z = 1
        *
        * This describes the plane in (X,Y,Z) space that intersects each axis at the
        * value 1.0; call this the chromaticity plane.  Thus the chromaticity
        * calculation has scaled each end-point so that it is on the x+y+z=1 plane
        * and chromaticity is the intersection of the vector from the origin to the
        * (X,Y,Z) value with the chromaticity plane.
        *
        * To fully invert the chromaticity calculation we would need the three
        * end-point scale factors, (red-scale, green-scale, blue-scale), but these
        * were not recorded.  Instead we calculated the reference white (X,Y,Z) and
        * recorded the chromaticity of this.  The reference white (X,Y,Z) would have
        * given all three of the scale factors since:
        *
        *    color-C = color-c * color-scale
        *    white-C = red-C + green-C + blue-C
        *            = red-c*red-scale + green-c*green-scale + blue-c*blue-scale
        *
        * But cHRM records only white-x and white-y, so we have lost the white scale
        * factor:
        *
        *    white-C = white-c*white-scale
        *
        * To handle this the inverse transformation makes an arbitrary assumption
        * about white-scale:
        *
        *    Assume: white-Y = 1.0
        *    Hence:  white-scale = 1/white-y
        *    Or:     red-Y + green-Y + blue-Y = 1.0
        *
        * Notice the last statement of the assumption gives an equation in three of
        * the nine values we want to calculate.  8 more equations come from the
        * above routine as summarised at the top above (the chromaticity
        * calculation):
        *
        *    Given: color-x = color-X / (color-X + color-Y + color-Z)
        *    Hence: (color-x - 1)*color-X + color.x*color-Y + color.x*color-Z = 0
        *
        * This is 9 simultaneous equations in the 9 variables "color-C" and can be
        * solved by Cramer's rule.  Cramer's rule requires calculating 10 9x9 matrix
        * determinants, however this is not as bad as it seems because only 28 of
        * the total of 90 terms in the various matrices are non-zero.  Nevertheless
        * Cramer's rule is notoriously numerically unstable because the determinant
        * calculation involves the difference of large, but similar, numbers.  It is
        * difficult to be sure that the calculation is stable for real world values
        * and it is certain that it becomes unstable where the end points are close
        * together.
        *
        * So this code uses the perhaps slightly less optimal but more
        * understandable and totally obvious approach of calculating color-scale.
        *
        * This algorithm depends on the precision in white-scale and that is
        * (1/white-y), so we can immediately see that as white-y approaches 0 the
        * accuracy inherent in the cHRM chunk drops off substantially.
        *
        * libpng arithmetic: a simple invertion of the above equations
        * ------------------------------------------------------------
        *
        *    white_scale = 1/white-y
        *    white-X = white-x * white-scale
        *    white-Y = 1.0
        *    white-Z = (1 - white-x - white-y) * white_scale
        *
        *    white-C = red-C + green-C + blue-C
        *            = red-c*red-scale + green-c*green-scale + blue-c*blue-scale
        *
        * This gives us three equations in (red-scale,green-scale,blue-scale) where
        * all the coefficients are now known:
        *
        *    red-x*red-scale + green-x*green-scale + blue-x*blue-scale
        *       = white-x/white-y
        *    red-y*red-scale + green-y*green-scale + blue-y*blue-scale = 1
        *    red-z*red-scale + green-z*green-scale + blue-z*blue-scale
        *       = (1 - white-x - white-y)/white-y
        *
        * In the last equation color-z is (1 - color-x - color-y) so we can add all
        * three equations together to get an alternative third:
        *
        *    red-scale + green-scale + blue-scale = 1/white-y = white-scale
        *
        * So now we have a Cramer's rule solution where the determinants are just
        * 3x3 - far more tractible.  Unfortunately 3x3 determinants still involve
        * multiplication of three coefficients so we can't guarantee to avoid
        * overflow in the libpng fixed point representation.  Using Cramer's rule in
        * floating point is probably a good choice here, but it's not an option for
        * fixed point.  Instead proceed to simplify the first two equations by
        * eliminating what is likely to be the largest value, blue-scale:
        *
        *    blue-scale = white-scale - red-scale - green-scale
        *
        * Hence:
        *
        *    (red-x - blue-x)*red-scale + (green-x - blue-x)*green-scale =
        *                (white-x - blue-x)*white-scale
        *
        *    (red-y - blue-y)*red-scale + (green-y - blue-y)*green-scale =
        *                1 - blue-y*white-scale
        *
        * And now we can trivially solve for (red-scale,green-scale):
        *
        *    green-scale =
        *                (white-x - blue-x)*white-scale - (red-x - blue-x)*red-scale
        *                -----------------------------------------------------------
        *                                  green-x - blue-x
        *
        *    red-scale =
        *                1 - blue-y*white-scale - (green-y - blue-y) * green-scale
        *                ---------------------------------------------------------
        *                                  red-y - blue-y
        *
        * Hence:
        *
        *    red-scale =
        *          ( (green-x - blue-x) * (white-y - blue-y) -
        *            (green-y - blue-y) * (white-x - blue-x) ) / white-y
        * -------------------------------------------------------------------------
        *  (green-x - blue-x)*(red-y - blue-y)-(green-y - blue-y)*(red-x - blue-x)
        *
        *    green-scale =
        *          ( (red-y - blue-y) * (white-x - blue-x) -
        *            (red-x - blue-x) * (white-y - blue-y) ) / white-y
        * -------------------------------------------------------------------------
        *  (green-x - blue-x)*(red-y - blue-y)-(green-y - blue-y)*(red-x - blue-x)
        *
        * Accuracy:
        * The input values have 5 decimal digits of accuracy.  The values are all in
        * the range 0 < value < 1, so simple products are in the same range but may
        * need up to 10 decimal digits to preserve the original precision and avoid
        * underflow.  Because we are using a 32-bit signed representation we cannot
        * match this; the best is a little over 9 decimal digits, less than 10.
        *
        * The approach used here is to preserve the maximum precision within the
        * signed representation.  Because the red-scale calculation above uses the
        * difference between two products of values that must be in the range -1..+1
        * it is sufficient to divide the product by 7; ceil(100,000/32767*2).  The
        * factor is irrelevant in the calculation because it is applied to both
        * numerator and denominator.
        *
        * Note that the values of the differences of the products of the
        * chromaticities in the above equations tend to be small, for example for
        * the sRGB chromaticities they are:
        *
        * red numerator:    -0.04751
        * green numerator:  -0.08788
        * denominator:      -0.2241 (without white-y multiplication)
        *
        *  The resultant Y coefficients from the chromaticities of some widely used
        *  color space definitions are (to 15 decimal places):
        *
        *  sRGB
        *    0.212639005871510 0.715168678767756 0.072192315360734
        *  Kodak ProPhoto
        *    0.288071128229293 0.711843217810102 0.000085653960605
        *  Adobe RGB
        *    0.297344975250536 0.627363566255466 0.075291458493998
        *  Adobe Wide Gamut RGB
        *    0.258728243040113 0.724682314948566 0.016589442011321
        */
       /* By the argument, above overflow should be impossible here. The return
        * value of 2 indicates an internal error to the caller.
        */
       if (!png_muldiv(&left, xy->greenx-xy->bluex, xy->redy - xy->bluey, 7))
          return 2;
       if (!png_muldiv(&right, xy->greeny-xy->bluey, xy->redx - xy->bluex, 7))
          return 2;
       denominator = left - right;

       /* Now find the red numerator. */
       if (!png_muldiv(&left, xy->greenx-xy->bluex, xy->whitey-xy->bluey, 7))
          return 2;
       if (!png_muldiv(&right, xy->greeny-xy->bluey, xy->whitex-xy->bluex, 7))
          return 2;

       /* Overflow is possible here and it indicates an extreme set of PNG cHRM
        * chunk values.  This calculation actually returns the reciprocal of the
        * scale value because this allows us to delay the multiplication of white-y
        * into the denominator, which tends to produce a small number.
        */
       if (!png_muldiv(&red_inverse, xy->whitey, denominator, left-right) ||
           red_inverse <= xy->whitey /* r+g+b scales = white scale */)
          return 1;

       /* Similarly for green_inverse: */
       if (!png_muldiv(&left, xy->redy-xy->bluey, xy->whitex-xy->bluex, 7))
          return 2;
       if (!png_muldiv(&right, xy->redx-xy->bluex, xy->whitey-xy->bluey, 7))
          return 2;
       if (!png_muldiv(&green_inverse, xy->whitey, denominator, left-right) ||
           green_inverse <= xy->whitey)
          return 1;

       /* And the blue scale, the checks above guarantee this can't overflow but it
        * can still produce 0 for extreme cHRM values.
        */
       blue_scale = png_reciprocal(xy->whitey) - png_reciprocal(red_inverse) -
          png_reciprocal(green_inverse);
       if (blue_scale <= 0) return 1;

       /* And fill in the png_XYZ: */
       if (!png_muldiv(&XYZ->red_X, xy->redx, PNG_FP_1, red_inverse)) return 1;
       if (!png_muldiv(&XYZ->red_Y, xy->redy, PNG_FP_1, red_inverse)) return 1;
       if (!png_muldiv(&XYZ->red_Z, PNG_FP_1 - xy->redx - xy->redy, PNG_FP_1,
          red_inverse))
          return 1;

       if (!png_muldiv(&XYZ->green_X, xy->greenx, PNG_FP_1, green_inverse))
          return 1;
       if (!png_muldiv(&XYZ->green_Y, xy->greeny, PNG_FP_1, green_inverse))
          return 1;
       if (!png_muldiv(&XYZ->green_Z, PNG_FP_1 - xy->greenx - xy->greeny, PNG_FP_1,
          green_inverse))
          return 1;

       if (!png_muldiv(&XYZ->blue_X, xy->bluex, blue_scale, PNG_FP_1)) return 1;
       if (!png_muldiv(&XYZ->blue_Y, xy->bluey, blue_scale, PNG_FP_1)) return 1;
       if (!png_muldiv(&XYZ->blue_Z, PNG_FP_1 - xy->bluex - xy->bluey, blue_scale,
          PNG_FP_1))
          return 1;

       return 0; /*success*/
    }

    static int
    png_XYZ_normalize(png_XYZ *XYZ)
    {
       png_int_32 Y;

       if (XYZ->red_Y < 0 || XYZ->green_Y < 0 || XYZ->blue_Y < 0 ||
          XYZ->red_X < 0 || XYZ->green_X < 0 || XYZ->blue_X < 0 ||
          XYZ->red_Z < 0 || XYZ->green_Z < 0 || XYZ->blue_Z < 0)
          return 1;

       /* Normalize by scaling so the sum of the end-point Y values is PNG_FP_1.
        * IMPLEMENTATION NOTE: ANSI requires signed overflow not to occur, therefore
        * relying on addition of two positive values producing a negative one is not
        * safe.
        */
       Y = XYZ->red_Y;
       if (0x7fffffff - Y < XYZ->green_X) return 1;
       Y += XYZ->green_Y;
       if (0x7fffffff - Y < XYZ->blue_X) return 1;
       Y += XYZ->blue_Y;

       if (Y != PNG_FP_1)
       {
          if (!png_muldiv(&XYZ->red_X, XYZ->red_X, PNG_FP_1, Y)) return 1;
          if (!png_muldiv(&XYZ->red_Y, XYZ->red_Y, PNG_FP_1, Y)) return 1;
          if (!png_muldiv(&XYZ->red_Z, XYZ->red_Z, PNG_FP_1, Y)) return 1;

          if (!png_muldiv(&XYZ->green_X, XYZ->green_X, PNG_FP_1, Y)) return 1;
          if (!png_muldiv(&XYZ->green_Y, XYZ->green_Y, PNG_FP_1, Y)) return 1;
          if (!png_muldiv(&XYZ->green_Z, XYZ->green_Z, PNG_FP_1, Y)) return 1;

          if (!png_muldiv(&XYZ->blue_X, XYZ->blue_X, PNG_FP_1, Y)) return 1;
          if (!png_muldiv(&XYZ->blue_Y, XYZ->blue_Y, PNG_FP_1, Y)) return 1;
          if (!png_muldiv(&XYZ->blue_Z, XYZ->blue_Z, PNG_FP_1, Y)) return 1;
       }

       return 0;
    }

    static int
    png_colorspace_endpoints_match(const png_xy *xy1, const png_xy *xy2, int delta)
    {
       /* Allow an error of +/-0.01 (absolute value) on each chromaticity */
       return !(PNG_OUT_OF_RANGE(xy1->whitex, xy2->whitex,delta) ||
          PNG_OUT_OF_RANGE(xy1->whitey, xy2->whitey,delta) ||
          PNG_OUT_OF_RANGE(xy1->redx,   xy2->redx,  delta) ||
          PNG_OUT_OF_RANGE(xy1->redy,   xy2->redy,  delta) ||
          PNG_OUT_OF_RANGE(xy1->greenx, xy2->greenx,delta) ||
          PNG_OUT_OF_RANGE(xy1->greeny, xy2->greeny,delta) ||
          PNG_OUT_OF_RANGE(xy1->bluex,  xy2->bluex, delta) ||
          PNG_OUT_OF_RANGE(xy1->bluey,  xy2->bluey, delta));
    }

    /* Added in libpng-1.6.0, a different check for the validity of a set of cHRM
     * chunk chromaticities.  Earlier checks used to simply look for the overflow
     * condition (where the determinant of the matrix to solve for XYZ ends up zero
     * because the chromaticity values are not all distinct.)  Despite this it is
     * theoretically possible to produce chromaticities that are apparently valid
     * but that rapidly degrade to invalid, potentially crashing, sets because of
     * arithmetic inaccuracies when calculations are performed on them.  The new
     * check is to round-trip xy -> XYZ -> xy and then check that the result is
     * within a small percentage of the original.
     */
    static int
    png_colorspace_check_xy(png_XYZ *XYZ, const png_xy *xy)
    {
       int result;
       png_xy xy_test;

       /* As a side-effect this routine also returns the XYZ endpoints. */
       result = png_XYZ_from_xy(XYZ, xy);
       if (result) return result;

       result = png_xy_from_XYZ(&xy_test, XYZ);
       if (result) return result;

       if (png_colorspace_endpoints_match(xy, &xy_test,
          5/*actually, the math is pretty accurate*/))
          return 0;

       /* Too much slip */
       return 1;
    }

    /* This is the check going the other way.  The XYZ is modified to normalize it
     * (another side-effect) and the xy chromaticities are returned.
     */
    static int
    png_colorspace_check_XYZ(png_xy *xy, png_XYZ *XYZ)
    {
       int result;
       png_XYZ XYZtemp;

       result = png_XYZ_normalize(XYZ);
       if (result) return result;

       result = png_xy_from_XYZ(xy, XYZ);
       if (result) return result;

       XYZtemp = *XYZ;
       return png_colorspace_check_xy(&XYZtemp, xy);
    }

    /* Used to check for an endpoint match against sRGB */
    static const png_xy sRGB_xy = /* From ITU-R BT.709-3 */
    {
       /* color      x       y */
       /* red   */ 64000, 33000,
       /* green */ 30000, 60000,
       /* blue  */ 15000,  6000,
       /* white */ 31270, 32900
    };

    static int
    png_colorspace_set_xy_and_XYZ(png_const_structrp png_ptr,
       png_colorspacerp colorspace, const png_xy *xy, const png_XYZ *XYZ,
       int preferred)
    {
       if (colorspace->flags & PNG_COLORSPACE_INVALID)
          return 0;

       /* The consistency check is performed on the chromaticities; this factors out
        * variations because of the normalization (or not) of the end point Y
        * values.
        */
       if (preferred < 2 && (colorspace->flags & PNG_COLORSPACE_HAVE_ENDPOINTS))
       {
          /* The end points must be reasonably close to any we already have.  The
           * following allows an error of up to +/-.001
           */
          if (!png_colorspace_endpoints_match(xy, &colorspace->end_points_xy, 100))
          {
             colorspace->flags |= PNG_COLORSPACE_INVALID;
             png_benign_error(png_ptr, "inconsistent chromaticities");
             return 0; /* failed */
          }

          /* Only overwrite with preferred values */
          if (!preferred)
             return 1; /* ok, but no change */
       }

       colorspace->end_points_xy = *xy;
       colorspace->end_points_XYZ = *XYZ;
       colorspace->flags |= PNG_COLORSPACE_HAVE_ENDPOINTS;

       /* The end points are normally quoted to two decimal digits, so allow +/-0.01
        * on this test.
        */
       if (png_colorspace_endpoints_match(xy, &sRGB_xy, 1000))
          colorspace->flags |= PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB;

       else
          colorspace->flags &= PNG_COLORSPACE_CANCEL(
             PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB);

       return 2; /* ok and changed */
    }

    int /* PRIVATE */
    png_colorspace_set_chromaticities(png_const_structrp png_ptr,
       png_colorspacerp colorspace, const png_xy *xy, int preferred)
    {
       /* We must check the end points to ensure they are reasonable - in the past
        * color management systems have crashed as a result of getting bogus
        * colorant values, while this isn't the fault of libpng it is the
        * responsibility of libpng because PNG carries the bomb and libpng is in a
        * position to protect against it.
        */
       png_XYZ XYZ;

       switch (png_colorspace_check_xy(&XYZ, xy))
       {
          case 0: /* success */
             return png_colorspace_set_xy_and_XYZ(png_ptr, colorspace, xy, &XYZ,
                preferred);

          case 1:
             /* We can't invert the chromaticities so we can't produce value XYZ
              * values.  Likely as not a color management system will fail too.
              */
             colorspace->flags |= PNG_COLORSPACE_INVALID;
             png_benign_error(png_ptr, "invalid chromaticities");
             break;

          default:
             /* libpng is broken; this should be a warning but if it happens we
              * want error reports so for the moment it is an error.
              */
             colorspace->flags |= PNG_COLORSPACE_INVALID;
             png_error(png_ptr, "internal error checking chromaticities");
             break;
       }

       return 0; /* failed */
    }

    int /* PRIVATE */
    png_colorspace_set_endpoints(png_const_structrp png_ptr,
       png_colorspacerp colorspace, const png_XYZ *XYZ_in, int preferred)
    {
       png_XYZ XYZ = *XYZ_in;
       png_xy xy;

       switch (png_colorspace_check_XYZ(&xy, &XYZ))
       {
          case 0:
             return png_colorspace_set_xy_and_XYZ(png_ptr, colorspace, &xy, &XYZ,
                preferred);

          case 1:
             /* End points are invalid. */
             colorspace->flags |= PNG_COLORSPACE_INVALID;
             png_benign_error(png_ptr, "invalid end points");
             break;

          default:
             colorspace->flags |= PNG_COLORSPACE_INVALID;
             png_error(png_ptr, "internal error checking chromaticities");
             break;
       }

       return 0; /* failed */
    }

    #if defined(PNG_sRGB_SUPPORTED) || defined(PNG_iCCP_SUPPORTED)
    /* Error message generation */
    static char
    png_icc_tag_char(png_uint_32 byte)
    {
       byte &= 0xff;
       if (byte >= 32 && byte <= 126)
          return (char)byte;
       else
          return '?';
    }

    static void
    png_icc_tag_name(char *name, png_uint_32 tag)
    {
       name[0] = '\'';
       name[1] = png_icc_tag_char(tag >> 24);
       name[2] = png_icc_tag_char(tag >> 16);
       name[3] = png_icc_tag_char(tag >>  8);
       name[4] = png_icc_tag_char(tag      );
       name[5] = '\'';
    }

    static int
    is_ICC_signature_char(png_alloc_size_t it)
    {
       return it == 32 || (it >= 48 && it <= 57) || (it >= 65 && it <= 90) ||
          (it >= 97 && it <= 122);
    }

    static int is_ICC_signature(png_alloc_size_t it)
    {
       return is_ICC_signature_char(it >> 24) /* checks all the top bits */ &&
          is_ICC_signature_char((it >> 16) & 0xff) &&
          is_ICC_signature_char((it >> 8) & 0xff) &&
          is_ICC_signature_char(it & 0xff);
    }

    static int
    png_icc_profile_error(png_const_structrp png_ptr, png_colorspacerp colorspace,
       png_const_charp name, png_alloc_size_t value, png_const_charp reason)
    {
       size_t pos;
       char message[196]; /* see below for calculation */

       if (colorspace != NULL)
          colorspace->flags |= PNG_COLORSPACE_INVALID;

       pos = png_safecat(message, (sizeof message), 0, "profile '"); /* 9 chars */
       pos = png_safecat(message, pos+79, pos, name); /* Truncate to 79 chars */
       pos = png_safecat(message, (sizeof message), pos, "': "); /* +2 = 90 */
       if (is_ICC_signature(value))
       {
          /* So 'value' is at most 4 bytes and the following cast is safe */
          png_icc_tag_name(message+pos, (png_uint_32)value);
          pos += 6; /* total +8; less than the else clause */
          message[pos++] = ':';
          message[pos++] = ' ';
       }
    #  ifdef PNG_WARNINGS_SUPPORTED
       else
          {
             char number[PNG_NUMBER_BUFFER_SIZE]; /* +24 = 114*/

             pos = png_safecat(message, (sizeof message), pos,
                png_format_number(number, number+(sizeof number),
                   PNG_NUMBER_FORMAT_x, value));
             pos = png_safecat(message, (sizeof message), pos, "h: "); /*+2 = 116*/
          }
    #  endif
       /* The 'reason' is an arbitrary message, allow +79 maximum 195 */
       pos = png_safecat(message, (sizeof message), pos, reason);

       /* This is recoverable, but make it unconditionally an app_error on write to
        * avoid writing invalid ICC profiles into PNG files.  (I.e.  we handle them
        * on read, with a warning, but on write unless the app turns off
        * application errors the PNG won't be written.)
        */
       png_chunk_report(png_ptr, message,
          (colorspace != NULL) ? PNG_CHUNK_ERROR : PNG_CHUNK_WRITE_ERROR);

       return 0;
    }
    #endif /* sRGB || iCCP */

    #ifdef PNG_sRGB_SUPPORTED
    int /* PRIVATE */
    png_colorspace_set_sRGB(png_const_structrp png_ptr, png_colorspacerp colorspace,
       int intent)
    {
       /* sRGB sets known gamma, end points and (from the chunk) intent. */
       /* IMPORTANT: these are not necessarily the values found in an ICC profile
        * because ICC profiles store values adapted to a D50 environment; it is
        * expected that the ICC profile mediaWhitePointTag will be D50, see the
        * checks and code elsewhere to understand this better.
        *
        * These XYZ values, which are accurate to 5dp, produce rgb to gray
        * coefficients of (6968,23435,2366), which are reduced (because they add up
        * to 32769 not 32768) to (6968,23434,2366).  These are the values that
        * libpng has traditionally used (and are the best values given the 15bit
        * algorithm used by the rgb to gray code.)
        */
       static const png_XYZ sRGB_XYZ = /* D65 XYZ (*not* the D50 adapted values!) */
       {
          /* color      X      Y      Z */
          /* red   */ 41239, 21264,  1933,
          /* green */ 35758, 71517, 11919,
          /* blue  */ 18048,  7219, 95053
       };

       /* Do nothing if the colorspace is already invalidated. */
       if (colorspace->flags & PNG_COLORSPACE_INVALID)
          return 0;

       /* Check the intent, then check for existing settings.  It is valid for the
        * PNG file to have cHRM or gAMA chunks along with sRGB, but the values must
        * be consistent with the correct values.  If, however, this function is
        * called below because an iCCP chunk matches sRGB then it is quite
        * conceivable that an older app recorded incorrect gAMA and cHRM because of
        * an incorrect calculation based on the values in the profile - this does
        * *not* invalidate the profile (though it still produces an error, which can
        * be ignored.)
        */
       if (intent < 0 || intent >= PNG_sRGB_INTENT_LAST)
          return png_icc_profile_error(png_ptr, colorspace, "sRGB",
             (unsigned)intent, "invalid sRGB rendering intent");

       if ((colorspace->flags & PNG_COLORSPACE_HAVE_INTENT) != 0 &&
          colorspace->rendering_intent != intent)
          return png_icc_profile_error(png_ptr, colorspace, "sRGB",
             (unsigned)intent, "inconsistent rendering intents");

       if ((colorspace->flags & PNG_COLORSPACE_FROM_sRGB) != 0)
       {
          png_benign_error(png_ptr, "duplicate sRGB information ignored");
          return 0;
       }

       /* If the standard sRGB cHRM chunk does not match the one from the PNG file
        * warn but overwrite the value with the correct one.
        */
       if ((colorspace->flags & PNG_COLORSPACE_HAVE_ENDPOINTS) != 0 &&
          !png_colorspace_endpoints_match(&sRGB_xy, &colorspace->end_points_xy,
             100))
          png_chunk_report(png_ptr, "cHRM chunk does not match sRGB",
             PNG_CHUNK_ERROR);

       /* This check is just done for the error reporting - the routine always
        * returns true when the 'from' argument corresponds to sRGB (2).
        */
       (void)png_colorspace_check_gamma(png_ptr, colorspace, PNG_GAMMA_sRGB_INVERSE,
          2/*from sRGB*/);

       /* intent: bugs in GCC force 'int' to be used as the parameter type. */
       colorspace->rendering_intent = (png_uint_16)intent;
       colorspace->flags |= PNG_COLORSPACE_HAVE_INTENT;

       /* endpoints */
       colorspace->end_points_xy = sRGB_xy;
       colorspace->end_points_XYZ = sRGB_XYZ;
       colorspace->flags |=
          (PNG_COLORSPACE_HAVE_ENDPOINTS|PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB);

       /* gamma */
       colorspace->gamma = PNG_GAMMA_sRGB_INVERSE;
       colorspace->flags |= PNG_COLORSPACE_HAVE_GAMMA;

       /* Finally record that we have an sRGB profile */
       colorspace->flags |=
          (PNG_COLORSPACE_MATCHES_sRGB|PNG_COLORSPACE_FROM_sRGB);

       return 1; /* set */
    }
    #endif /* sRGB */

    #ifdef PNG_iCCP_SUPPORTED
    /* Encoded value of D50 as an ICC XYZNumber.  From the ICC 2010 spec the value
     * is XYZ(0.9642,1.0,0.8249), which scales to:
     *
     *    (63189.8112, 65536, 54060.6464)
     */
    static const png_byte D50_nCIEXYZ[12] =
       { 0x00, 0x00, 0xf6, 0xd6, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0xd3, 0x2d };

    int /* PRIVATE */
    png_icc_check_length(png_const_structrp png_ptr, png_colorspacerp colorspace,
       png_const_charp name, png_uint_32 profile_length)
    {
       if (profile_length < 132)
          return png_icc_profile_error(png_ptr, colorspace, name, profile_length,
             "too short");

       if (profile_length & 3)
          return png_icc_profile_error(png_ptr, colorspace, name, profile_length,
             "invalid length");

       return 1;
    }

    int /* PRIVATE */
    png_icc_check_header(png_const_structrp png_ptr, png_colorspacerp colorspace,
       png_const_charp name, png_uint_32 profile_length,
       png_const_bytep profile/* first 132 bytes only */, int color_type)
    {
       png_uint_32 temp;

       /* Length check; this cannot be ignored in this code because profile_length
        * is used later to check the tag table, so even if the profile seems over
        * long profile_length from the caller must be correct.  The caller can fix
        * this up on read or write by just passing in the profile header length.
        */
       temp = png_get_uint_32(profile);
       if (temp != profile_length)
          return png_icc_profile_error(png_ptr, colorspace, name, temp,
             "length does not match profile");

       temp = png_get_uint_32(profile+128); /* tag count: 12 bytes/tag */
       if (temp > 357913930 || /* (2^32-4-132)/12: maximum possible tag count */
          profile_length < 132+12*temp) /* truncated tag table */
          return png_icc_profile_error(png_ptr, colorspace, name, temp,
             "tag count too large");

       /* The 'intent' must be valid or we can't store it, ICC limits the intent to
        * 16 bits.
        */
       temp = png_get_uint_32(profile+64);
       if (temp >= 0xffff) /* The ICC limit */
          return png_icc_profile_error(png_ptr, colorspace, name, temp,
             "invalid rendering intent");

       /* This is just a warning because the profile may be valid in future
        * versions.
        */
       if (temp >= PNG_sRGB_INTENT_LAST)
          (void)png_icc_profile_error(png_ptr, NULL, name, temp,
             "intent outside defined range");

       /* At this point the tag table can't be checked because it hasn't necessarily
        * been loaded; however, various header fields can be checked.  These checks
        * are for values permitted by the PNG spec in an ICC profile; the PNG spec
        * restricts the profiles that can be passed in an iCCP chunk (they must be
        * appropriate to processing PNG data!)
        */

       /* Data checks (could be skipped).  These checks must be independent of the
        * version number; however, the version number doesn't accomodate changes in
        * the header fields (just the known tags and the interpretation of the
        * data.)
        */
       temp = png_get_uint_32(profile+36); /* signature 'ascp' */
       if (temp != 0x61637370)
          return png_icc_profile_error(png_ptr, colorspace, name, temp,
             "invalid signature");

       /* Currently the PCS illuminant/adopted white point (the computational
        * white point) are required to be D50,
        * however the profile contains a record of the illuminant so perhaps ICC
        * expects to be able to change this in the future (despite the rationale in
        * the introduction for using a fixed PCS adopted white.)  Consequently the
        * following is just a warning.
        */
       if (memcmp(profile+68, D50_nCIEXYZ, 12) != 0)
          (void)png_icc_profile_error(png_ptr, NULL, name, 0/*no tag value*/,
             "PCS illuminant is not D50");

       /* The PNG spec requires this:
        * "If the iCCP chunk is present, the image samples conform to the colour
        * space represented by the embedded ICC profile as defined by the
        * International Color Consortium [ICC]. The colour space of the ICC profile
        * shall be an RGB colour space for colour images (PNG colour types 2, 3, and
        * 6), or a greyscale colour space for greyscale images (PNG colour types 0
        * and 4)."
        *
        * This checking code ensures the embedded profile (on either read or write)
        * conforms to the specification requirements.  Notice that an ICC 'gray'
        * color-space profile contains the information to transform the monochrome
        * data to XYZ or L*a*b (according to which PCS the profile uses) and this
        * should be used in preference to the standard libpng K channel replication
        * into R, G and B channels.
        *
        * Previously it was suggested that an RGB profile on grayscale data could be
        * handled.  However it it is clear that using an RGB profile in this context
        * must be an error - there is no specification of what it means.  Thus it is
        * almost certainly more correct to ignore the profile.
        */
       temp = png_get_uint_32(profile+16); /* data colour space field */
       switch (temp)
       {
          case 0x52474220: /* 'RGB ' */
             if (!(color_type & PNG_COLOR_MASK_COLOR))
                return png_icc_profile_error(png_ptr, colorspace, name, temp,
                   "RGB color space not permitted on grayscale PNG");
             break;

          case 0x47524159: /* 'GRAY' */
             if (color_type & PNG_COLOR_MASK_COLOR)
                return png_icc_profile_error(png_ptr, colorspace, name, temp,
                   "Gray color space not permitted on RGB PNG");
             break;

          default:
             return png_icc_profile_error(png_ptr, colorspace, name, temp,
                "invalid ICC profile color space");
       }

       /* It is up to the application to check that the profile class matches the
        * application requirements; the spec provides no guidance, but it's pretty
        * weird if the profile is not scanner ('scnr'), monitor ('mntr'), printer
        * ('prtr') or 'spac' (for generic color spaces).  Issue a warning in these
        * cases.  Issue an error for device link or abstract profiles - these don't
        * contain the records necessary to transform the color-space to anything
        * other than the target device (and not even that for an abstract profile).
        * Profiles of these classes may not be embedded in images.
        */
       temp = png_get_uint_32(profile+12); /* profile/device class */
       switch (temp)
       {
          case 0x73636E72: /* 'scnr' */
          case 0x6D6E7472: /* 'mntr' */
          case 0x70727472: /* 'prtr' */
          case 0x73706163: /* 'spac' */
             /* All supported */
             break;

          case 0x61627374: /* 'abst' */
             /* May not be embedded in an image */
             return png_icc_profile_error(png_ptr, colorspace, name, temp,
                "invalid embedded Abstract ICC profile");

          case 0x6C696E6B: /* 'link' */
             /* DeviceLink profiles cannnot be interpreted in a non-device specific
              * fashion, if an app uses the AToB0Tag in the profile the results are
              * undefined unless the result is sent to the intended device,
              * therefore a DeviceLink profile should not be found embedded in a
              * PNG.
              */
             return png_icc_profile_error(png_ptr, colorspace, name, temp,
                "unexpected DeviceLink ICC profile class");

          case 0x6E6D636C: /* 'nmcl' */
             /* A NamedColor profile is also device specific, however it doesn't
              * contain an AToB0 tag that is open to misintrepretation.  Almost
              * certainly it will fail the tests below.
              */
             (void)png_icc_profile_error(png_ptr, NULL, name, temp,
                "unexpected NamedColor ICC profile class");
             break;

          default:
             /* To allow for future enhancements to the profile accept unrecognized
              * profile classes with a warning, these then hit the test below on the
              * tag content to ensure they are backward compatible with one of the
              * understood profiles.
              */
             (void)png_icc_profile_error(png_ptr, NULL, name, temp,
                "unrecognized ICC profile class");
             break;
       }

       /* For any profile other than a device link one the PCS must be encoded
        * either in XYZ or Lab.
        */
       temp = png_get_uint_32(profile+20);
       switch (temp)
       {
          case 0x58595A20: /* 'XYZ ' */
          case 0x4C616220: /* 'Lab ' */
             break;

          default:
             return png_icc_profile_error(png_ptr, colorspace, name, temp,
                "unexpected ICC PCS encoding");
       }

       return 1;
    }

    int /* PRIVATE */
    png_icc_check_tag_table(png_const_structrp png_ptr, png_colorspacerp colorspace,
       png_const_charp name, png_uint_32 profile_length,
       png_const_bytep profile /* header plus whole tag table */)
    {
       png_uint_32 tag_count = png_get_uint_32(profile+128);
       png_uint_32 itag;
       png_const_bytep tag = profile+132; /* The first tag */

       /* First scan all the tags in the table and add bits to the icc_info value
        * (temporarily in 'tags').
        */
       for (itag=0; itag < tag_count; ++itag, tag += 12)
       {
          png_uint_32 tag_id = png_get_uint_32(tag+0);
          png_uint_32 tag_start = png_get_uint_32(tag+4); /* must be aligned */
          png_uint_32 tag_length = png_get_uint_32(tag+8);/* not padded */

          /* The ICC specification does not exclude zero length tags, therefore the
           * start might actually be anywhere if there is no data, but this would be
           * a clear abuse of the intent of the standard so the start is checked for
           * being in range.  All defined tag types have an 8 byte header - a 4 byte
           * type signature then 0.
           */
          if ((tag_start & 3) != 0)
          {
             /* CNHP730S.icc shipped with Microsoft Windows 64 violates this, it is
              * only a warning here because libpng does not care about the
              * alignment.
              */
             (void)png_icc_profile_error(png_ptr, NULL, name, tag_id,
                "ICC profile tag start not a multiple of 4");
          }

          /* This is a hard error; potentially it can cause read outside the
           * profile.
           */
          if (tag_start > profile_length || tag_length > profile_length - tag_start)
             return png_icc_profile_error(png_ptr, colorspace, name, tag_id,
                "ICC profile tag outside profile");
       }

       return 1; /* success, maybe with warnings */
    }

    #ifdef PNG_sRGB_SUPPORTED
    /* Information about the known ICC sRGB profiles */
    static const struct
    {
       png_uint_32 adler, crc, length;
       png_uint_32 md5[4];
       png_byte    have_md5;
       png_byte    is_broken;
       png_uint_16 intent;

    #  define PNG_MD5(a,b,c,d) { a, b, c, d }, (a!=0)||(b!=0)||(c!=0)||(d!=0)
    #  define PNG_ICC_CHECKSUM(adler, crc, md5, intent, broke, date, length, fname)\
          { adler, crc, length, md5, broke, intent },

    } png_sRGB_checks[] =
    {
       /* This data comes from contrib/tools/checksum-icc run on downloads of
        * all four ICC sRGB profiles from www.color.org.
        */
       /* adler32, crc32, MD5[4], intent, date, length, file-name */
       PNG_ICC_CHECKSUM(0x0a3fd9f6, 0x3b8772b9,
          PNG_MD5(0x29f83dde, 0xaff255ae, 0x7842fae4, 0xca83390d), 0, 0,
          "2009/03/27 21:36:31", 3048, "sRGB_IEC61966-2-1_black_scaled.icc")

       /* ICC sRGB v2 perceptual no black-compensation: */
       PNG_ICC_CHECKSUM(0x4909e5e1, 0x427ebb21,
          PNG_MD5(0xc95bd637, 0xe95d8a3b, 0x0df38f99, 0xc1320389), 1, 0,
          "2009/03/27 21:37:45", 3052, "sRGB_IEC61966-2-1_no_black_scaling.icc")

       PNG_ICC_CHECKSUM(0xfd2144a1, 0x306fd8ae,
          PNG_MD5(0xfc663378, 0x37e2886b, 0xfd72e983, 0x8228f1b8), 0, 0,
          "2009/08/10 17:28:01", 60988, "sRGB_v4_ICC_preference_displayclass.icc")

       /* ICC sRGB v4 perceptual */
       PNG_ICC_CHECKSUM(0x209c35d2, 0xbbef7812,
          PNG_MD5(0x34562abf, 0x994ccd06, 0x6d2c5721, 0xd0d68c5d), 0, 0,
          "2007/07/25 00:05:37", 60960, "sRGB_v4_ICC_preference.icc")

       /* The following profiles have no known MD5 checksum. If there is a match
        * on the (empty) MD5 the other fields are used to attempt a match and
        * a warning is produced.  The first two of these profiles have a 'cprt' tag
        * which suggests that they were also made by Hewlett Packard.
        */
       PNG_ICC_CHECKSUM(0xa054d762, 0x5d5129ce,
          PNG_MD5(0x00000000, 0x00000000, 0x00000000, 0x00000000), 1, 0,
          "2004/07/21 18:57:42", 3024, "sRGB_IEC61966-2-1_noBPC.icc")

       /* This is a 'mntr' (display) profile with a mediaWhitePointTag that does not
        * match the D50 PCS illuminant in the header (it is in fact the D65 values,
        * so the white point is recorded as the un-adapted value.)  The profiles
        * below only differ in one byte - the intent - and are basically the same as
        * the previous profile except for the mediaWhitePointTag error and a missing
        * chromaticAdaptationTag.
        */
       PNG_ICC_CHECKSUM(0xf784f3fb, 0x182ea552,
          PNG_MD5(0x00000000, 0x00000000, 0x00000000, 0x00000000), 0, 1/*broken*/,
          "1998/02/09 06:49:00", 3144, "HP-Microsoft sRGB v2 perceptual")

       PNG_ICC_CHECKSUM(0x0398f3fc, 0xf29e526d,
          PNG_MD5(0x00000000, 0x00000000, 0x00000000, 0x00000000), 1, 1/*broken*/,
          "1998/02/09 06:49:00", 3144, "HP-Microsoft sRGB v2 media-relative")
    };

    static int
    png_compare_ICC_profile_with_sRGB(png_const_structrp png_ptr,
       png_const_bytep profile, uLong adler)
    {
       /* The quick check is to verify just the MD5 signature and trust the
        * rest of the data.  Because the profile has already been verified for
        * correctness this is safe.  png_colorspace_set_sRGB will check the 'intent'
        * field too, so if the profile has been edited with an intent not defined
        * by sRGB (but maybe defined by a later ICC specification) the read of
        * the profile will fail at that point.
        */
       png_uint_32 length = 0;
       png_uint_32 intent = 0x10000; /* invalid */
    #if PNG_sRGB_PROFILE_CHECKS > 1
       uLong crc = 0; /* the value for 0 length data */
    #endif
       unsigned int i;

       for (i=0; i < (sizeof png_sRGB_checks) / (sizeof png_sRGB_checks[0]); ++i)
       {
          if (png_get_uint_32(profile+84) == png_sRGB_checks[i].md5[0] &&
             png_get_uint_32(profile+88) == png_sRGB_checks[i].md5[1] &&
             png_get_uint_32(profile+92) == png_sRGB_checks[i].md5[2] &&
             png_get_uint_32(profile+96) == png_sRGB_checks[i].md5[3])
          {
             /* This may be one of the old HP profiles without an MD5, in that
              * case we can only use the length and Adler32 (note that these
              * are not used by default if there is an MD5!)
              */
    #        if PNG_sRGB_PROFILE_CHECKS == 0
                if (png_sRGB_checks[i].have_md5)
                   return 1+png_sRGB_checks[i].is_broken;
    #        endif

             /* Profile is unsigned or more checks have been configured in. */
             if (length == 0)
             {
                length = png_get_uint_32(profile);
                intent = png_get_uint_32(profile+64);
             }

             /* Length *and* intent must match */
             if (length == png_sRGB_checks[i].length &&
                intent == png_sRGB_checks[i].intent)
             {
                /* Now calculate the adler32 if not done already. */
                if (adler == 0)
                {
                   adler = adler32(0, NULL, 0);
                   adler = adler32(adler, profile, length);
                }

                if (adler == png_sRGB_checks[i].adler)
                {
                   /* These basic checks suggest that the data has not been
                    * modified, but if the check level is more than 1 perform
                    * our own crc32 checksum on the data.
                    */
    #              if PNG_sRGB_PROFILE_CHECKS > 1
                      if (crc == 0)
                      {
                         crc = crc32(0, NULL, 0);
                         crc = crc32(crc, profile, length);
                      }

                      /* So this check must pass for the 'return' below to happen.
                       */
                      if (crc == png_sRGB_checks[i].crc)
    #              endif
                   {
                      if (png_sRGB_checks[i].is_broken)
                      {
                         /* These profiles are known to have bad data that may cause
                          * problems if they are used, therefore attempt to
                          * discourage their use, skip the 'have_md5' warning below,
                          * which is made irrelevant by this error.
                          */
                         png_chunk_report(png_ptr, "known incorrect sRGB profile",
                            PNG_CHUNK_ERROR);
                      }

                      /* Warn that this being done; this isn't even an error since
                       * the profile is perfectly valid, but it would be nice if
                       * people used the up-to-date ones.
                       */
                      else if (!png_sRGB_checks[i].have_md5)
                      {
                         png_chunk_report(png_ptr,
                            "out-of-date sRGB profile with no signature",
                            PNG_CHUNK_WARNING);
                      }

                      return 1+png_sRGB_checks[i].is_broken;
                   }
                }
             }

    #        if PNG_sRGB_PROFILE_CHECKS > 0
                /* The signature matched, but the profile had been changed in some
                 * way.  This is an apparent violation of the ICC terms of use and,
                 * anyway, probably indicates a data error or uninformed hacking.
                 */
                if (png_sRGB_checks[i].have_md5)
                   png_benign_error(png_ptr,
                      "copyright violation: edited ICC profile ignored");
    #        endif
          }
       }

       return 0; /* no match */
    }
    #endif

    #ifdef PNG_sRGB_SUPPORTED
    void /* PRIVATE */
    png_icc_set_sRGB(png_const_structrp png_ptr,
       png_colorspacerp colorspace, png_const_bytep profile, uLong adler)
    {
       /* Is this profile one of the known ICC sRGB profiles?  If it is, just set
        * the sRGB information.
        */
       if (png_compare_ICC_profile_with_sRGB(png_ptr, profile, adler))
          (void)png_colorspace_set_sRGB(png_ptr, colorspace,
             (int)/*already checked*/png_get_uint_32(profile+64));
    }
    #endif /* PNG_READ_sRGB_SUPPORTED */

    int /* PRIVATE */
    png_colorspace_set_ICC(png_const_structrp png_ptr, png_colorspacerp colorspace,
       png_const_charp name, png_uint_32 profile_length, png_const_bytep profile,
       int color_type)
    {
       if (colorspace->flags & PNG_COLORSPACE_INVALID)
          return 0;

       if (png_icc_check_length(png_ptr, colorspace, name, profile_length) &&
          png_icc_check_header(png_ptr, colorspace, name, profile_length, profile,
             color_type) &&
          png_icc_check_tag_table(png_ptr, colorspace, name, profile_length,
             profile))
       {
    #     ifdef PNG_sRGB_SUPPORTED
             /* If no sRGB support, don't try storing sRGB information */
             png_icc_set_sRGB(png_ptr, colorspace, profile, 0);
    #     endif
          return 1;
       }

       /* Failure case */
       return 0;
    }
    #endif /* iCCP */

    #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
    void /* PRIVATE */
    png_colorspace_set_rgb_coefficients(png_structrp png_ptr)
    {
       /* Set the rgb_to_gray coefficients from the colorspace. */
       if (!png_ptr->rgb_to_gray_coefficients_set &&
          (png_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_ENDPOINTS) != 0)
       {
          /* png_set_background has not been called, get the coefficients from the Y
           * values of the colorspace colorants.
           */
          png_fixed_point r = png_ptr->colorspace.end_points_XYZ.red_Y;
          png_fixed_point g = png_ptr->colorspace.end_points_XYZ.green_Y;
          png_fixed_point b = png_ptr->colorspace.end_points_XYZ.blue_Y;
          png_fixed_point total = r+g+b;

          if (total > 0 &&
             r >= 0 && png_muldiv(&r, r, 32768, total) && r >= 0 && r <= 32768 &&
             g >= 0 && png_muldiv(&g, g, 32768, total) && g >= 0 && g <= 32768 &&
             b >= 0 && png_muldiv(&b, b, 32768, total) && b >= 0 && b <= 32768 &&
             r+g+b <= 32769)
          {
             /* We allow 0 coefficients here.  r+g+b may be 32769 if two or
              * all of the coefficients were rounded up.  Handle this by
              * reducing the *largest* coefficient by 1; this matches the
              * approach used for the default coefficients in pngrtran.c
              */
             int add = 0;

             if (r+g+b > 32768)
                add = -1;
             else if (r+g+b < 32768)
                add = 1;

             if (add != 0)
             {
                if (g >= r && g >= b)
                   g += add;
                else if (r >= g && r >= b)
                   r += add;
                else
                   b += add;
             }

             /* Check for an internal error. */
             if (r+g+b != 32768)
                png_error(png_ptr,
                   "internal error handling cHRM coefficients");

             else
             {
                png_ptr->rgb_to_gray_red_coeff   = (png_uint_16)r;
                png_ptr->rgb_to_gray_green_coeff = (png_uint_16)g;
             }
          }

          /* This is a png_error at present even though it could be ignored -
           * it should never happen, but it is important that if it does, the
           * bug is fixed.
           */
          else
             png_error(png_ptr, "internal error handling cHRM->XYZ");
       }
    }
    #endif

    #endif /* COLORSPACE */

    void /* PRIVATE */
    png_check_IHDR(png_const_structrp png_ptr,
       png_uint_32 width, png_uint_32 height, int bit_depth,
       int color_type, int interlace_type, int compression_type,
       int filter_type)
    {
       int error = 0;

       /* Check for width and height valid values */
       if (width == 0)
       {
          png_warning(png_ptr, "Image width is zero in IHDR");
          error = 1;
       }

       if (height == 0)
       {
          png_warning(png_ptr, "Image height is zero in IHDR");
          error = 1;
       }

    #  ifdef PNG_SET_USER_LIMITS_SUPPORTED
       if (width > png_ptr->user_width_max)

    #  else
       if (width > PNG_USER_WIDTH_MAX)
    #  endif
       {
          png_warning(png_ptr, "Image width exceeds user limit in IHDR");
          error = 1;
       }

    #  ifdef PNG_SET_USER_LIMITS_SUPPORTED
       if (height > png_ptr->user_height_max)
    #  else
       if (height > PNG_USER_HEIGHT_MAX)
    #  endif
       {
          png_warning(png_ptr, "Image height exceeds user limit in IHDR");
          error = 1;
       }

       if (width > PNG_UINT_31_MAX)
       {
          png_warning(png_ptr, "Invalid image width in IHDR");
          error = 1;
       }

       if (height > PNG_UINT_31_MAX)
       {
          png_warning(png_ptr, "Invalid image height in IHDR");
          error = 1;
       }

       if (width > (PNG_UINT_32_MAX
                     >> 3)      /* 8-byte RGBA pixels */
                     - 48       /* bigrowbuf hack */
                     - 1        /* filter byte */
                     - 7*8      /* rounding of width to multiple of 8 pixels */
                     - 8)       /* extra max_pixel_depth pad */
          png_warning(png_ptr, "Width is too large for libpng to process pixels");

       /* Check other values */
       if (bit_depth != 1 && bit_depth != 2 && bit_depth != 4 &&
           bit_depth != 8 && bit_depth != 16)
       {
          png_warning(png_ptr, "Invalid bit depth in IHDR");
          error = 1;
       }

       if (color_type < 0 || color_type == 1 ||
           color_type == 5 || color_type > 6)
       {
          png_warning(png_ptr, "Invalid color type in IHDR");
          error = 1;
       }

       if (((color_type == PNG_COLOR_TYPE_PALETTE) && bit_depth > 8) ||
           ((color_type == PNG_COLOR_TYPE_RGB ||
             color_type == PNG_COLOR_TYPE_GRAY_ALPHA ||
             color_type == PNG_COLOR_TYPE_RGB_ALPHA) && bit_depth < 8))
       {
          png_warning(png_ptr, "Invalid color type/bit depth combination in IHDR");
          error = 1;
       }

       if (interlace_type >= PNG_INTERLACE_LAST)
       {
          png_warning(png_ptr, "Unknown interlace method in IHDR");
          error = 1;
       }

       if (compression_type != PNG_COMPRESSION_TYPE_BASE)
       {
          png_warning(png_ptr, "Unknown compression method in IHDR");
          error = 1;
       }

    #  ifdef PNG_MNG_FEATURES_SUPPORTED
       /* Accept filter_method 64 (intrapixel differencing) only if
        * 1. Libpng was compiled with PNG_MNG_FEATURES_SUPPORTED and
        * 2. Libpng did not read a PNG signature (this filter_method is only
        *    used in PNG datastreams that are embedded in MNG datastreams) and
        * 3. The application called png_permit_mng_features with a mask that
        *    included PNG_FLAG_MNG_FILTER_64 and
        * 4. The filter_method is 64 and
        * 5. The color_type is RGB or RGBA
        */
       if ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) &&
           png_ptr->mng_features_permitted)
          png_warning(png_ptr, "MNG features are not allowed in a PNG datastream");

       if (filter_type != PNG_FILTER_TYPE_BASE)
       {
          if (!((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&
              (filter_type == PNG_INTRAPIXEL_DIFFERENCING) &&
              ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) == 0) &&
              (color_type == PNG_COLOR_TYPE_RGB ||
              color_type == PNG_COLOR_TYPE_RGB_ALPHA)))
          {
             png_warning(png_ptr, "Unknown filter method in IHDR");
             error = 1;
          }

          if (png_ptr->mode & PNG_HAVE_PNG_SIGNATURE)
          {
             png_warning(png_ptr, "Invalid filter method in IHDR");
             error = 1;
          }
       }

    #  else
       if (filter_type != PNG_FILTER_TYPE_BASE)
       {
          png_warning(png_ptr, "Unknown filter method in IHDR");
          error = 1;
       }
    #  endif

       if (error == 1)
          png_error(png_ptr, "Invalid IHDR data");
    }

    #if defined(PNG_sCAL_SUPPORTED) || defined(PNG_pCAL_SUPPORTED)
    /* ASCII to fp functions */
    /* Check an ASCII formated floating point value, see the more detailed
     * comments in pngpriv.h
     */
    /* The following is used internally to preserve the sticky flags */
    #define png_fp_add(state, flags) ((state) |= (flags))
    #define png_fp_set(state, value) ((state) = (value) | ((state) & PNG_FP_STICKY))

    int /* PRIVATE */
    png_check_fp_number(png_const_charp string, png_size_t size, int *statep,
       png_size_tp whereami)
    {
       int state = *statep;
       png_size_t i = *whereami;

       while (i < size)
       {
          int type;
          /* First find the type of the next character */
          switch (string[i])
          {
          case 43:  type = PNG_FP_SAW_SIGN;                   break;
          case 45:  type = PNG_FP_SAW_SIGN + PNG_FP_NEGATIVE; break;
          case 46:  type = PNG_FP_SAW_DOT;                    break;
          case 48:  type = PNG_FP_SAW_DIGIT;                  break;
          case 49: case 50: case 51: case 52:
          case 53: case 54: case 55: case 56:
          case 57:  type = PNG_FP_SAW_DIGIT + PNG_FP_NONZERO; break;
          case 69:
          case 101: type = PNG_FP_SAW_E;                      break;
          default:  goto PNG_FP_End;
          }

          /* Now deal with this type according to the current
           * state, the type is arranged to not overlap the
           * bits of the PNG_FP_STATE.
           */
          switch ((state & PNG_FP_STATE) + (type & PNG_FP_SAW_ANY))
          {
          case PNG_FP_INTEGER + PNG_FP_SAW_SIGN:
             if (state & PNG_FP_SAW_ANY)
                goto PNG_FP_End; /* not a part of the number */

             png_fp_add(state, type);
             break;

          case PNG_FP_INTEGER + PNG_FP_SAW_DOT:
             /* Ok as trailer, ok as lead of fraction. */
             if (state & PNG_FP_SAW_DOT) /* two dots */
                goto PNG_FP_End;

             else if (state & PNG_FP_SAW_DIGIT) /* trailing dot? */
                png_fp_add(state, type);

             else
                png_fp_set(state, PNG_FP_FRACTION | type);

             break;

          case PNG_FP_INTEGER + PNG_FP_SAW_DIGIT:
             if (state & PNG_FP_SAW_DOT) /* delayed fraction */
                png_fp_set(state, PNG_FP_FRACTION | PNG_FP_SAW_DOT);

             png_fp_add(state, type | PNG_FP_WAS_VALID);

             break;

          case PNG_FP_INTEGER + PNG_FP_SAW_E:
             if ((state & PNG_FP_SAW_DIGIT) == 0)
                goto PNG_FP_End;

             png_fp_set(state, PNG_FP_EXPONENT);

             break;

       /* case PNG_FP_FRACTION + PNG_FP_SAW_SIGN:
             goto PNG_FP_End; ** no sign in fraction */

       /* case PNG_FP_FRACTION + PNG_FP_SAW_DOT:
             goto PNG_FP_End; ** Because SAW_DOT is always set */

          case PNG_FP_FRACTION + PNG_FP_SAW_DIGIT:
             png_fp_add(state, type | PNG_FP_WAS_VALID);
             break;

          case PNG_FP_FRACTION + PNG_FP_SAW_E:
             /* This is correct because the trailing '.' on an
              * integer is handled above - so we can only get here
              * with the sequence ".E" (with no preceding digits).
              */
             if ((state & PNG_FP_SAW_DIGIT) == 0)
                goto PNG_FP_End;

             png_fp_set(state, PNG_FP_EXPONENT);

             break;

          case PNG_FP_EXPONENT + PNG_FP_SAW_SIGN:
             if (state & PNG_FP_SAW_ANY)
                goto PNG_FP_End; /* not a part of the number */

             png_fp_add(state, PNG_FP_SAW_SIGN);

             break;

       /* case PNG_FP_EXPONENT + PNG_FP_SAW_DOT:
             goto PNG_FP_End; */

          case PNG_FP_EXPONENT + PNG_FP_SAW_DIGIT:
             png_fp_add(state, PNG_FP_SAW_DIGIT | PNG_FP_WAS_VALID);

             break;

       /* case PNG_FP_EXPONEXT + PNG_FP_SAW_E:
             goto PNG_FP_End; */

          default: goto PNG_FP_End; /* I.e. break 2 */
          }

          /* The character seems ok, continue. */
          ++i;
       }

    PNG_FP_End:
       /* Here at the end, update the state and return the correct
        * return code.
        */
       *statep = state;
       *whereami = i;

       return (state & PNG_FP_SAW_DIGIT) != 0;
    }

    /* The same but for a complete string. */
    int
    png_check_fp_string(png_const_charp string, png_size_t size)
    {
       int        state=0;
       png_size_t char_index=0;

       if (png_check_fp_number(string, size, &state, &char_index) &&
          (char_index == size || string[char_index] == 0))
          return state /* must be non-zero - see above */;

       return 0; /* i.e. fail */
    }
    #endif /* pCAL or sCAL */

    #ifdef PNG_sCAL_SUPPORTED
    #  ifdef PNG_FLOATING_POINT_SUPPORTED
    /* Utility used below - a simple accurate power of ten from an integral
     * exponent.
     */
    static double
    png_pow10(int power)
    {
       int recip = 0;
       double d = 1;

       /* Handle negative exponent with a reciprocal at the end because
        * 10 is exact whereas .1 is inexact in base 2
        */
       if (power < 0)
       {
          if (power < DBL_MIN_10_EXP) return 0;
          recip = 1, power = -power;
       }

       if (power > 0)
       {
          /* Decompose power bitwise. */
          double mult = 10;
          do
          {
             if (power & 1) d *= mult;
             mult *= mult;
             power >>= 1;
          }
          while (power > 0);

          if (recip) d = 1/d;
       }
       /* else power is 0 and d is 1 */

       return d;
    }

    /* Function to format a floating point value in ASCII with a given
     * precision.
     */
    void /* PRIVATE */
    png_ascii_from_fp(png_const_structrp png_ptr, png_charp ascii, png_size_t size,
        double fp, unsigned int precision)
    {
       /* We use standard functions from math.h, but not printf because
        * that would require stdio.  The caller must supply a buffer of
        * sufficient size or we will png_error.  The tests on size and
        * the space in ascii[] consumed are indicated below.
        */
       if (precision < 1)
          precision = DBL_DIG;

       /* Enforce the limit of the implementation precision too. */
       if (precision > DBL_DIG+1)
          precision = DBL_DIG+1;

       /* Basic sanity checks */
       if (size >= precision+5) /* See the requirements below. */
       {
          if (fp < 0)
          {
             fp = -fp;
             *ascii++ = 45; /* '-'  PLUS 1 TOTAL 1 */
             --size;
          }

          if (fp >= DBL_MIN && fp <= DBL_MAX)
          {
             int exp_b10;       /* A base 10 exponent */
             double base;   /* 10^exp_b10 */

             /* First extract a base 10 exponent of the number,
              * the calculation below rounds down when converting
              * from base 2 to base 10 (multiply by log10(2) -
              * 0.3010, but 77/256 is 0.3008, so exp_b10 needs to
              * be increased.  Note that the arithmetic shift
              * performs a floor() unlike C arithmetic - using a
              * C multiply would break the following for negative
              * exponents.
              */
             (void)frexp(fp, &exp_b10); /* exponent to base 2 */

             exp_b10 = (exp_b10 * 77) >> 8; /* <= exponent to base 10 */

             /* Avoid underflow here. */
             base = png_pow10(exp_b10); /* May underflow */

             while (base < DBL_MIN || base < fp)
             {
                /* And this may overflow. */
                double test = png_pow10(exp_b10+1);

                if (test <= DBL_MAX)
                   ++exp_b10, base = test;

                else
                   break;
             }

             /* Normalize fp and correct exp_b10, after this fp is in the
              * range [.1,1) and exp_b10 is both the exponent and the digit
              * *before* which the decimal point should be inserted
              * (starting with 0 for the first digit).  Note that this
              * works even if 10^exp_b10 is out of range because of the
              * test on DBL_MAX above.
              */
             fp /= base;
             while (fp >= 1) fp /= 10, ++exp_b10;

             /* Because of the code above fp may, at this point, be
              * less than .1, this is ok because the code below can
              * handle the leading zeros this generates, so no attempt
              * is made to correct that here.
              */

             {
                int czero, clead, cdigits;
                char exponent[10];

                /* Allow up to two leading zeros - this will not lengthen
                 * the number compared to using E-n.
                 */
                if (exp_b10 < 0 && exp_b10 > -3) /* PLUS 3 TOTAL 4 */
                {
                   czero = -exp_b10; /* PLUS 2 digits: TOTAL 3 */
                   exp_b10 = 0;      /* Dot added below before first output. */
                }
                else
                   czero = 0;    /* No zeros to add */

                /* Generate the digit list, stripping trailing zeros and
                 * inserting a '.' before a digit if the exponent is 0.
                 */
                clead = czero; /* Count of leading zeros */
                cdigits = 0;   /* Count of digits in list. */

                do
                {
                   double d;

                   fp *= 10;
                   /* Use modf here, not floor and subtract, so that
                    * the separation is done in one step.  At the end
                    * of the loop don't break the number into parts so
                    * that the final digit is rounded.
                    */
                   if (cdigits+czero-clead+1 < (int)precision)
                      fp = modf(fp, &d);

                   else
                   {
                      d = floor(fp + .5);

                      if (d > 9)
                      {
                         /* Rounding up to 10, handle that here. */
                         if (czero > 0)
                         {
                            --czero, d = 1;
                            if (cdigits == 0) --clead;
                         }
                         else
                         {
                            while (cdigits > 0 && d > 9)
                            {
                               int ch = *--ascii;

                               if (exp_b10 != (-1))
                                  ++exp_b10;

                               else if (ch == 46)
                               {
                                  ch = *--ascii, ++size;
                                  /* Advance exp_b10 to '1', so that the
                                   * decimal point happens after the
                                   * previous digit.
                                   */
                                  exp_b10 = 1;
                               }

                               --cdigits;
                               d = ch - 47;  /* I.e. 1+(ch-48) */
                            }

                            /* Did we reach the beginning? If so adjust the
                             * exponent but take into account the leading
                             * decimal point.
                             */
                            if (d > 9)  /* cdigits == 0 */
                            {
                               if (exp_b10 == (-1))
                               {
                                  /* Leading decimal point (plus zeros?), if
                                   * we lose the decimal point here it must
                                   * be reentered below.
                                   */
                                  int ch = *--ascii;

                                  if (ch == 46)
                                     ++size, exp_b10 = 1;

                                  /* Else lost a leading zero, so 'exp_b10' is
                                   * still ok at (-1)
                                   */
                               }
                               else
                                  ++exp_b10;

                               /* In all cases we output a '1' */
                               d = 1;
                            }
                         }
                      }
                      fp = 0; /* Guarantees termination below. */
                   }

                   if (d == 0)
                   {
                      ++czero;
                      if (cdigits == 0) ++clead;
                   }
                   else
                   {
                      /* Included embedded zeros in the digit count. */
                      cdigits += czero - clead;
                      clead = 0;

                      while (czero > 0)
                      {
                         /* exp_b10 == (-1) means we just output the decimal
                          * place - after the DP don't adjust 'exp_b10' any
                          * more!
                          */
                         if (exp_b10 != (-1))
                         {
                            if (exp_b10 == 0) *ascii++ = 46, --size;
                            /* PLUS 1: TOTAL 4 */
                            --exp_b10;
                         }
                         *ascii++ = 48, --czero;
                      }

                      if (exp_b10 != (-1))
                      {
                         if (exp_b10 == 0) *ascii++ = 46, --size; /* counted
                                                                     above */
                         --exp_b10;
                      }
                      *ascii++ = (char)(48 + (int)d), ++cdigits;
                   }
                }
                while (cdigits+czero-clead < (int)precision && fp > DBL_MIN);

                /* The total output count (max) is now 4+precision */

                /* Check for an exponent, if we don't need one we are
                 * done and just need to terminate the string.  At
                 * this point exp_b10==(-1) is effectively if flag - it got
                 * to '-1' because of the decrement after outputing
                 * the decimal point above (the exponent required is
                 * *not* -1!)
                 */
                if (exp_b10 >= (-1) && exp_b10 <= 2)
                {
                   /* The following only happens if we didn't output the
                    * leading zeros above for negative exponent, so this
                    * doest add to the digit requirement.  Note that the
                    * two zeros here can only be output if the two leading
                    * zeros were *not* output, so this doesn't increase
                    * the output count.
                    */
                   while (--exp_b10 >= 0) *ascii++ = 48;

                   *ascii = 0;

                   /* Total buffer requirement (including the '\0') is
                    * 5+precision - see check at the start.
                    */
                   return;
                }

                /* Here if an exponent is required, adjust size for
                 * the digits we output but did not count.  The total
                 * digit output here so far is at most 1+precision - no
                 * decimal point and no leading or trailing zeros have
                 * been output.
                 */
                size -= cdigits;

                *ascii++ = 69, --size;    /* 'E': PLUS 1 TOTAL 2+precision */

                /* The following use of an unsigned temporary avoids ambiguities in
                 * the signed arithmetic on exp_b10 and permits GCC at least to do
                 * better optimization.
                 */
                {
                   unsigned int uexp_b10;

                   if (exp_b10 < 0)
                   {
                      *ascii++ = 45, --size; /* '-': PLUS 1 TOTAL 3+precision */
                      uexp_b10 = -exp_b10;
                   }

                   else
                      uexp_b10 = exp_b10;

                   cdigits = 0;

                   while (uexp_b10 > 0)
                   {
                      exponent[cdigits++] = (char)(48 + uexp_b10 % 10);
                      uexp_b10 /= 10;
                   }
                }

                /* Need another size check here for the exponent digits, so
                 * this need not be considered above.
                 */
                if ((int)size > cdigits)
                {
                   while (cdigits > 0) *ascii++ = exponent[--cdigits];

                   *ascii = 0;

                   return;
                }
             }
          }
          else if (!(fp >= DBL_MIN))
          {
             *ascii++ = 48; /* '0' */
             *ascii = 0;
             return;
          }
          else
          {
             *ascii++ = 105; /* 'i' */
             *ascii++ = 110; /* 'n' */
             *ascii++ = 102; /* 'f' */
             *ascii = 0;
             return;
          }
       }

       /* Here on buffer too small. */
       png_error(png_ptr, "ASCII conversion buffer too small");
    }

    #  endif /* FLOATING_POINT */

    #  ifdef PNG_FIXED_POINT_SUPPORTED
    /* Function to format a fixed point value in ASCII.
     */
    void /* PRIVATE */
    png_ascii_from_fixed(png_const_structrp png_ptr, png_charp ascii,
        png_size_t size, png_fixed_point fp)
    {
       /* Require space for 10 decimal digits, a decimal point, a minus sign and a
        * trailing \0, 13 characters:
        */
       if (size > 12)
       {
          png_uint_32 num;

          /* Avoid overflow here on the minimum integer. */
          if (fp < 0)
             *ascii++ = 45, --size, num = -fp;
          else
             num = fp;

          if (num <= 0x80000000) /* else overflowed */
          {
             unsigned int ndigits = 0, first = 16 /* flag value */;
             char digits[10];

             while (num)
             {
                /* Split the low digit off num: */
                unsigned int tmp = num/10;
                num -= tmp*10;
                digits[ndigits++] = (char)(48 + num);
                /* Record the first non-zero digit, note that this is a number
                 * starting at 1, it's not actually the array index.
                 */
                if (first == 16 && num > 0)
                   first = ndigits;
                num = tmp;
             }

             if (ndigits > 0)
             {
                while (ndigits > 5) *ascii++ = digits[--ndigits];
                /* The remaining digits are fractional digits, ndigits is '5' or
                 * smaller at this point.  It is certainly not zero.  Check for a
                 * non-zero fractional digit:
                 */
                if (first <= 5)
                {
                   unsigned int i;
                   *ascii++ = 46; /* decimal point */
                   /* ndigits may be <5 for small numbers, output leading zeros
                    * then ndigits digits to first:
                    */
                   i = 5;
                   while (ndigits < i) *ascii++ = 48, --i;
                   while (ndigits >= first) *ascii++ = digits[--ndigits];
                   /* Don't output the trailing zeros! */
                }
             }
             else
                *ascii++ = 48;

             /* And null terminate the string: */
             *ascii = 0;
             return;
          }
       }

       /* Here on buffer too small. */
       png_error(png_ptr, "ASCII conversion buffer too small");
    }
    #   endif /* FIXED_POINT */
    #endif /* READ_SCAL */

    #if defined(PNG_FLOATING_POINT_SUPPORTED) && \
       !defined(PNG_FIXED_POINT_MACRO_SUPPORTED) && \
       (defined(PNG_gAMA_SUPPORTED) || defined(PNG_cHRM_SUPPORTED) || \
       defined(PNG_sCAL_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED) || \
       defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)) || \
       (defined(PNG_sCAL_SUPPORTED) && \
       defined(PNG_FLOATING_ARITHMETIC_SUPPORTED))
    png_fixed_point
    png_fixed(png_const_structrp png_ptr, double fp, png_const_charp text)
    {
       double r = floor(100000 * fp + .5);

       if (r > 2147483647. || r < -2147483648.)
          png_fixed_error(png_ptr, text);

       return (png_fixed_point)r;
    }
    #endif

    #if defined(PNG_READ_GAMMA_SUPPORTED) || \
        defined(PNG_INCH_CONVERSIONS_SUPPORTED) || defined(PNG_READ_pHYs_SUPPORTED)
    /* muldiv functions */
    /* This API takes signed arguments and rounds the result to the nearest
     * integer (or, for a fixed point number - the standard argument - to
     * the nearest .00001).  Overflow and divide by zero are signalled in
     * the result, a boolean - true on success, false on overflow.
     */
    int
    png_muldiv(png_fixed_point_p res, png_fixed_point a, png_int_32 times,
        png_int_32 divisor)
    {
       /* Return a * times / divisor, rounded. */
       if (divisor != 0)
       {
          if (a == 0 || times == 0)
          {
             *res = 0;
             return 1;
          }
          else
          {
    #ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
             double r = a;
             r *= times;
             r /= divisor;
             r = floor(r+.5);

             /* A png_fixed_point is a 32-bit integer. */
             if (r <= 2147483647. && r >= -2147483648.)
             {
                *res = (png_fixed_point)r;
                return 1;
             }
    #else
             int negative = 0;
             png_uint_32 A, T, D;
             png_uint_32 s16, s32, s00;

             if (a < 0)
                negative = 1, A = -a;
             else
                A = a;

             if (times < 0)
                negative = !negative, T = -times;
             else
                T = times;

             if (divisor < 0)
                negative = !negative, D = -divisor;
             else
                D = divisor;

             /* Following can't overflow because the arguments only
              * have 31 bits each, however the result may be 32 bits.
              */
             s16 = (A >> 16) * (T & 0xffff) +
                               (A & 0xffff) * (T >> 16);
             /* Can't overflow because the a*times bit is only 30
              * bits at most.
              */
             s32 = (A >> 16) * (T >> 16) + (s16 >> 16);
             s00 = (A & 0xffff) * (T & 0xffff);

             s16 = (s16 & 0xffff) << 16;
             s00 += s16;

             if (s00 < s16)
                ++s32; /* carry */

             if (s32 < D) /* else overflow */
             {
                /* s32.s00 is now the 64-bit product, do a standard
                 * division, we know that s32 < D, so the maximum
                 * required shift is 31.
                 */
                int bitshift = 32;
                png_fixed_point result = 0; /* NOTE: signed */

                while (--bitshift >= 0)
                {
                   png_uint_32 d32, d00;

                   if (bitshift > 0)
                      d32 = D >> (32-bitshift), d00 = D << bitshift;

                   else
                      d32 = 0, d00 = D;

                   if (s32 > d32)
                   {
                      if (s00 < d00) --s32; /* carry */
                      s32 -= d32, s00 -= d00, result += 1<<bitshift;
                   }

                   else
                      if (s32 == d32 && s00 >= d00)
                         s32 = 0, s00 -= d00, result += 1<<bitshift;
                }

                /* Handle the rounding. */
                if (s00 >= (D >> 1))
                   ++result;

                if (negative)
                   result = -result;

                /* Check for overflow. */
                if ((negative && result <= 0) || (!negative && result >= 0))
                {
                   *res = result;
                   return 1;
                }
             }
    #endif
          }
       }

       return 0;
    }
    #endif /* READ_GAMMA || INCH_CONVERSIONS */

    #if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_INCH_CONVERSIONS_SUPPORTED)
    /* The following is for when the caller doesn't much care about the
     * result.
     */
    png_fixed_point
    png_muldiv_warn(png_const_structrp png_ptr, png_fixed_point a, png_int_32 times,
        png_int_32 divisor)
    {
       png_fixed_point result;

       if (png_muldiv(&result, a, times, divisor))
          return result;

       png_warning(png_ptr, "fixed point overflow ignored");
       return 0;
    }
    #endif

    #ifdef PNG_GAMMA_SUPPORTED /* more fixed point functions for gamma */
    /* Calculate a reciprocal, return 0 on div-by-zero or overflow. */
    png_fixed_point
    png_reciprocal(png_fixed_point a)
    {
    #ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
       double r = floor(1E10/a+.5);

       if (r <= 2147483647. && r >= -2147483648.)
          return (png_fixed_point)r;
    #else
       png_fixed_point res;

       if (png_muldiv(&res, 100000, 100000, a))
          return res;
    #endif

       return 0; /* error/overflow */
    }

    /* This is the shared test on whether a gamma value is 'significant' - whether
     * it is worth doing gamma correction.
     */
    int /* PRIVATE */
    png_gamma_significant(png_fixed_point gamma_val)
    {
       return gamma_val < PNG_FP_1 - PNG_GAMMA_THRESHOLD_FIXED ||
           gamma_val > PNG_FP_1 + PNG_GAMMA_THRESHOLD_FIXED;
    }
    #endif

    #ifdef PNG_READ_GAMMA_SUPPORTED
    /* A local convenience routine. */
    static png_fixed_point
    png_product2(png_fixed_point a, png_fixed_point b)
    {
       /* The required result is 1/a * 1/b; the following preserves accuracy. */
    #ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
       double r = a * 1E-5;
       r *= b;
       r = floor(r+.5);

       if (r <= 2147483647. && r >= -2147483648.)
          return (png_fixed_point)r;
    #else
       png_fixed_point res;

       if (png_muldiv(&res, a, b, 100000))
          return res;
    #endif

       return 0; /* overflow */
    }

    /* The inverse of the above. */
    png_fixed_point
    png_reciprocal2(png_fixed_point a, png_fixed_point b)
    {
       /* The required result is 1/a * 1/b; the following preserves accuracy. */
    #ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
       double r = 1E15/a;
       r /= b;
       r = floor(r+.5);

       if (r <= 2147483647. && r >= -2147483648.)
          return (png_fixed_point)r;
    #else
       /* This may overflow because the range of png_fixed_point isn't symmetric,
        * but this API is only used for the product of file and screen gamma so it
        * doesn't matter that the smallest number it can produce is 1/21474, not
        * 1/100000
        */
       png_fixed_point res = png_product2(a, b);

       if (res != 0)
          return png_reciprocal(res);
    #endif

       return 0; /* overflow */
    }
    #endif /* READ_GAMMA */

    #ifdef PNG_READ_GAMMA_SUPPORTED /* gamma table code */
    #ifndef PNG_FLOATING_ARITHMETIC_SUPPORTED
    /* Fixed point gamma.
     *
     * The code to calculate the tables used below can be found in the shell script
     * contrib/tools/intgamma.sh
     *
     * To calculate gamma this code implements fast log() and exp() calls using only
     * fixed point arithmetic.  This code has sufficient precision for either 8-bit
     * or 16-bit sample values.
     *
     * The tables used here were calculated using simple 'bc' programs, but C double
     * precision floating point arithmetic would work fine.
     *
     * 8-bit log table
     *   This is a table of -log(value/255)/log(2) for 'value' in the range 128 to
     *   255, so it's the base 2 logarithm of a normalized 8-bit floating point
     *   mantissa.  The numbers are 32-bit fractions.
     */
    static const png_uint_32
    png_8bit_l2[128] =
    {
       4270715492U, 4222494797U, 4174646467U, 4127164793U, 4080044201U, 4033279239U,
       3986864580U, 3940795015U, 3895065449U, 3849670902U, 3804606499U, 3759867474U,
       3715449162U, 3671346997U, 3627556511U, 3584073329U, 3540893168U, 3498011834U,
       3455425220U, 3413129301U, 3371120137U, 3329393864U, 3287946700U, 3246774933U,
       3205874930U, 3165243125U, 3124876025U, 3084770202U, 3044922296U, 3005329011U,
       2965987113U, 2926893432U, 2888044853U, 2849438323U, 2811070844U, 2772939474U,
       2735041326U, 2697373562U, 2659933400U, 2622718104U, 2585724991U, 2548951424U,
       2512394810U, 2476052606U, 2439922311U, 2404001468U, 2368287663U, 2332778523U,
       2297471715U, 2262364947U, 2227455964U, 2192742551U, 2158222529U, 2123893754U,
       2089754119U, 2055801552U, 2022034013U, 1988449497U, 1955046031U, 1921821672U,
       1888774511U, 1855902668U, 1823204291U, 1790677560U, 1758320682U, 1726131893U,
       1694109454U, 1662251657U, 1630556815U, 1599023271U, 1567649391U, 1536433567U,
       1505374214U, 1474469770U, 1443718700U, 1413119487U, 1382670639U, 1352370686U,
       1322218179U, 1292211689U, 1262349810U, 1232631153U, 1203054352U, 1173618059U,
       1144320946U, 1115161701U, 1086139034U, 1057251672U, 1028498358U, 999877854U,
       971388940U, 943030410U, 914801076U, 886699767U, 858725327U, 830876614U,
       803152505U, 775551890U, 748073672U, 720716771U, 693480120U, 666362667U,
       639363374U, 612481215U, 585715177U, 559064263U, 532527486U, 506103872U,
       479792461U, 453592303U, 427502463U, 401522014U, 375650043U, 349885648U,
       324227938U, 298676034U, 273229066U, 247886176U, 222646516U, 197509248U,
       172473545U, 147538590U, 122703574U, 97967701U, 73330182U, 48790236U,
       24347096U, 0U

    #if 0
       /* The following are the values for 16-bit tables - these work fine for the
        * 8-bit conversions but produce very slightly larger errors in the 16-bit
        * log (about 1.2 as opposed to 0.7 absolute error in the final value).  To
        * use these all the shifts below must be adjusted appropriately.
        */
       65166, 64430, 63700, 62976, 62257, 61543, 60835, 60132, 59434, 58741, 58054,
       57371, 56693, 56020, 55352, 54689, 54030, 53375, 52726, 52080, 51439, 50803,
       50170, 49542, 48918, 48298, 47682, 47070, 46462, 45858, 45257, 44661, 44068,
       43479, 42894, 42312, 41733, 41159, 40587, 40020, 39455, 38894, 38336, 37782,
       37230, 36682, 36137, 35595, 35057, 34521, 33988, 33459, 32932, 32408, 31887,
       31369, 30854, 30341, 29832, 29325, 28820, 28319, 27820, 27324, 26830, 26339,
       25850, 25364, 24880, 24399, 23920, 23444, 22970, 22499, 22029, 21562, 21098,
       20636, 20175, 19718, 19262, 18808, 18357, 17908, 17461, 17016, 16573, 16132,
       15694, 15257, 14822, 14390, 13959, 13530, 13103, 12678, 12255, 11834, 11415,
       10997, 10582, 10168, 9756, 9346, 8937, 8531, 8126, 7723, 7321, 6921, 6523,
       6127, 5732, 5339, 4947, 4557, 4169, 3782, 3397, 3014, 2632, 2251, 1872, 1495,
       1119, 744, 372
    #endif
    };

    static png_int_32
    png_log8bit(unsigned int x)
    {
       unsigned int lg2 = 0;
       /* Each time 'x' is multiplied by 2, 1 must be subtracted off the final log,
        * because the log is actually negate that means adding 1.  The final
        * returned value thus has the range 0 (for 255 input) to 7.994 (for 1
        * input), return -1 for the overflow (log 0) case, - so the result is
        * always at most 19 bits.
        */
       if ((x &= 0xff) == 0)
          return -1;

       if ((x & 0xf0) == 0)
          lg2  = 4, x <<= 4;

       if ((x & 0xc0) == 0)
          lg2 += 2, x <<= 2;

       if ((x & 0x80) == 0)
          lg2 += 1, x <<= 1;

       /* result is at most 19 bits, so this cast is safe: */
       return (png_int_32)((lg2 << 16) + ((png_8bit_l2[x-128]+32768)>>16));
    }

    /* The above gives exact (to 16 binary places) log2 values for 8-bit images,
     * for 16-bit images we use the most significant 8 bits of the 16-bit value to
     * get an approximation then multiply the approximation by a correction factor
     * determined by the remaining up to 8 bits.  This requires an additional step
     * in the 16-bit case.
     *
     * We want log2(value/65535), we have log2(v'/255), where:
     *
     *    value = v' * 256 + v''
     *          = v' * f
     *
     * So f is value/v', which is equal to (256+v''/v') since v' is in the range 128
     * to 255 and v'' is in the range 0 to 255 f will be in the range 256 to less
     * than 258.  The final factor also needs to correct for the fact that our 8-bit
     * value is scaled by 255, whereas the 16-bit values must be scaled by 65535.
     *
     * This gives a final formula using a calculated value 'x' which is value/v' and
     * scaling by 65536 to match the above table:
     *
     *   log2(x/257) * 65536
     *
     * Since these numbers are so close to '1' we can use simple linear
     * interpolation between the two end values 256/257 (result -368.61) and 258/257
     * (result 367.179).  The values used below are scaled by a further 64 to give
     * 16-bit precision in the interpolation:
     *
     * Start (256): -23591
     * Zero  (257):      0
     * End   (258):  23499
     */
    static png_int_32
    png_log16bit(png_uint_32 x)
    {
       unsigned int lg2 = 0;

       /* As above, but now the input has 16 bits. */
       if ((x &= 0xffff) == 0)
          return -1;

       if ((x & 0xff00) == 0)
          lg2  = 8, x <<= 8;

       if ((x & 0xf000) == 0)
          lg2 += 4, x <<= 4;

       if ((x & 0xc000) == 0)
          lg2 += 2, x <<= 2;

       if ((x & 0x8000) == 0)
          lg2 += 1, x <<= 1;

       /* Calculate the base logarithm from the top 8 bits as a 28-bit fractional
        * value.
        */
       lg2 <<= 28;
       lg2 += (png_8bit_l2[(x>>8)-128]+8) >> 4;

       /* Now we need to interpolate the factor, this requires a division by the top
        * 8 bits.  Do this with maximum precision.
        */
       x = ((x << 16) + (x >> 9)) / (x >> 8);

       /* Since we divided by the top 8 bits of 'x' there will be a '1' at 1<<24,
        * the value at 1<<16 (ignoring this) will be 0 or 1; this gives us exactly
        * 16 bits to interpolate to get the low bits of the result.  Round the
        * answer.  Note that the end point values are scaled by 64 to retain overall
        * precision and that 'lg2' is current scaled by an extra 12 bits, so adjust
        * the overall scaling by 6-12.  Round at every step.
        */
       x -= 1U << 24;

       if (x <= 65536U) /* <= '257' */
          lg2 += ((23591U * (65536U-x)) + (1U << (16+6-12-1))) >> (16+6-12);

       else
          lg2 -= ((23499U * (x-65536U)) + (1U << (16+6-12-1))) >> (16+6-12);

       /* Safe, because the result can't have more than 20 bits: */
       return (png_int_32)((lg2 + 2048) >> 12);
    }

    /* The 'exp()' case must invert the above, taking a 20-bit fixed point
     * logarithmic value and returning a 16 or 8-bit number as appropriate.  In
     * each case only the low 16 bits are relevant - the fraction - since the
     * integer bits (the top 4) simply determine a shift.
     *
     * The worst case is the 16-bit distinction between 65535 and 65534, this
     * requires perhaps spurious accuracty in the decoding of the logarithm to
     * distinguish log2(65535/65534.5) - 10^-5 or 17 bits.  There is little chance
     * of getting this accuracy in practice.
     *
     * To deal with this the following exp() function works out the exponent of the
     * frational part of the logarithm by using an accurate 32-bit value from the
     * top four fractional bits then multiplying in the remaining bits.
     */
    static const png_uint_32
    png_32bit_exp[16] =
    {
       /* NOTE: the first entry is deliberately set to the maximum 32-bit value. */
       4294967295U, 4112874773U, 3938502376U, 3771522796U, 3611622603U, 3458501653U,
       3311872529U, 3171459999U, 3037000500U, 2908241642U, 2784941738U, 2666869345U,
       2553802834U, 2445529972U, 2341847524U, 2242560872U
    };

    /* Adjustment table; provided to explain the numbers in the code below. */
    #if 0
    for (i=11;i>=0;--i){ print i, " ", (1 - e(-(2^i)/65536*l(2))) * 2^(32-i), "\n"}
       11 44937.64284865548751208448
       10 45180.98734845585101160448
        9 45303.31936980687359311872
        8 45364.65110595323018870784
        7 45395.35850361789624614912
        6 45410.72259715102037508096
        5 45418.40724413220722311168
        4 45422.25021786898173001728
        3 45424.17186732298419044352
        2 45425.13273269940811464704
        1 45425.61317555035558641664
        0 45425.85339951654943850496
    #endif

    static png_uint_32
    png_exp(png_fixed_point x)
    {
       if (x > 0 && x <= 0xfffff) /* Else overflow or zero (underflow) */
       {
          /* Obtain a 4-bit approximation */
          png_uint_32 e = png_32bit_exp[(x >> 12) & 0xf];

          /* Incorporate the low 12 bits - these decrease the returned value by
           * multiplying by a number less than 1 if the bit is set.  The multiplier
           * is determined by the above table and the shift. Notice that the values
           * converge on 45426 and this is used to allow linear interpolation of the
           * low bits.
           */
          if (x & 0x800)
             e -= (((e >> 16) * 44938U) +  16U) >> 5;

          if (x & 0x400)
             e -= (((e >> 16) * 45181U) +  32U) >> 6;

          if (x & 0x200)
             e -= (((e >> 16) * 45303U) +  64U) >> 7;

          if (x & 0x100)
             e -= (((e >> 16) * 45365U) + 128U) >> 8;

          if (x & 0x080)
             e -= (((e >> 16) * 45395U) + 256U) >> 9;

          if (x & 0x040)
             e -= (((e >> 16) * 45410U) + 512U) >> 10;

          /* And handle the low 6 bits in a single block. */
          e -= (((e >> 16) * 355U * (x & 0x3fU)) + 256U) >> 9;

          /* Handle the upper bits of x. */
          e >>= x >> 16;
          return e;
       }

       /* Check for overflow */
       if (x <= 0)
          return png_32bit_exp[0];

       /* Else underflow */
       return 0;
    }

    static png_byte
    png_exp8bit(png_fixed_point lg2)
    {
       /* Get a 32-bit value: */
       png_uint_32 x = png_exp(lg2);

       /* Convert the 32-bit value to 0..255 by multiplying by 256-1, note that the
        * second, rounding, step can't overflow because of the first, subtraction,
        * step.
        */
       x -= x >> 8;
       return (png_byte)((x + 0x7fffffU) >> 24);
    }

    static png_uint_16
    png_exp16bit(png_fixed_point lg2)
    {
       /* Get a 32-bit value: */
       png_uint_32 x = png_exp(lg2);

       /* Convert the 32-bit value to 0..65535 by multiplying by 65536-1: */
       x -= x >> 16;
       return (png_uint_16)((x + 32767U) >> 16);
    }
    #endif /* FLOATING_ARITHMETIC */

    png_byte
    png_gamma_8bit_correct(unsigned int value, png_fixed_point gamma_val)
    {
       if (value > 0 && value < 255)
       {
    #     ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
             double r = floor(255*pow(value/255.,gamma_val*.00001)+.5);
             return (png_byte)r;
    #     else
             png_int_32 lg2 = png_log8bit(value);
             png_fixed_point res;

             if (png_muldiv(&res, gamma_val, lg2, PNG_FP_1))
                return png_exp8bit(res);

             /* Overflow. */
             value = 0;
    #     endif
       }

       return (png_byte)value;
    }

    png_uint_16
    png_gamma_16bit_correct(unsigned int value, png_fixed_point gamma_val)
    {
       if (value > 0 && value < 65535)
       {
    #     ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
             double r = floor(65535*pow(value/65535.,gamma_val*.00001)+.5);
             return (png_uint_16)r;
    #     else
             png_int_32 lg2 = png_log16bit(value);
             png_fixed_point res;

             if (png_muldiv(&res, gamma_val, lg2, PNG_FP_1))
                return png_exp16bit(res);

             /* Overflow. */
             value = 0;
    #     endif
       }

       return (png_uint_16)value;
    }

    /* This does the right thing based on the bit_depth field of the
     * png_struct, interpreting values as 8-bit or 16-bit.  While the result
     * is nominally a 16-bit value if bit depth is 8 then the result is
     * 8-bit (as are the arguments.)
     */
    png_uint_16 /* PRIVATE */
    png_gamma_correct(png_structrp png_ptr, unsigned int value,
        png_fixed_point gamma_val)
    {
       if (png_ptr->bit_depth == 8)
          return png_gamma_8bit_correct(value, gamma_val);

       else
          return png_gamma_16bit_correct(value, gamma_val);
    }

    /* Internal function to build a single 16-bit table - the table consists of
     * 'num' 256 entry subtables, where 'num' is determined by 'shift' - the amount
     * to shift the input values right (or 16-number_of_signifiant_bits).
     *
     * The caller is responsible for ensuring that the table gets cleaned up on
     * png_error (i.e. if one of the mallocs below fails) - i.e. the *table argument
     * should be somewhere that will be cleaned.
     */
    static void
    png_build_16bit_table(png_structrp png_ptr, png_uint_16pp *ptable,
       PNG_CONST unsigned int shift, PNG_CONST png_fixed_point gamma_val)
    {
       /* Various values derived from 'shift': */
       PNG_CONST unsigned int num = 1U << (8U - shift);
       PNG_CONST unsigned int max = (1U << (16U - shift))-1U;
       PNG_CONST unsigned int max_by_2 = 1U << (15U-shift);
       unsigned int i;

       png_uint_16pp table = *ptable =
           (png_uint_16pp)png_calloc(png_ptr, num * (sizeof (png_uint_16p)));

       for (i = 0; i < num; i++)
       {
          png_uint_16p sub_table = table[i] =
              (png_uint_16p)png_malloc(png_ptr, 256 * (sizeof (png_uint_16)));

          /* The 'threshold' test is repeated here because it can arise for one of
           * the 16-bit tables even if the others don't hit it.
           */
          if (png_gamma_significant(gamma_val))
          {
             /* The old code would overflow at the end and this would cause the
              * 'pow' function to return a result >1, resulting in an
              * arithmetic error.  This code follows the spec exactly; ig is
              * the recovered input sample, it always has 8-16 bits.
              *
              * We want input * 65535/max, rounded, the arithmetic fits in 32
              * bits (unsigned) so long as max <= 32767.
              */
             unsigned int j;
             for (j = 0; j < 256; j++)
             {
                png_uint_32 ig = (j << (8-shift)) + i;
    #           ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
                   /* Inline the 'max' scaling operation: */
                   double d = floor(65535*pow(ig/(double)max, gamma_val*.00001)+.5);
                   sub_table[j] = (png_uint_16)d;
    #           else
                   if (shift)
                      ig = (ig * 65535U + max_by_2)/max;

                   sub_table[j] = png_gamma_16bit_correct(ig, gamma_val);
    #           endif
             }
          }
          else
          {
             /* We must still build a table, but do it the fast way. */
             unsigned int j;

             for (j = 0; j < 256; j++)
             {
                png_uint_32 ig = (j << (8-shift)) + i;

                if (shift)
                   ig = (ig * 65535U + max_by_2)/max;

                sub_table[j] = (png_uint_16)ig;
             }
          }
       }
    }

    /* NOTE: this function expects the *inverse* of the overall gamma transformation
     * required.
     */
    static void
    png_build_16to8_table(png_structrp png_ptr, png_uint_16pp *ptable,
       PNG_CONST unsigned int shift, PNG_CONST png_fixed_point gamma_val)
    {
       PNG_CONST unsigned int num = 1U << (8U - shift);
       PNG_CONST unsigned int max = (1U << (16U - shift))-1U;
       unsigned int i;
       png_uint_32 last;

       png_uint_16pp table = *ptable =
           (png_uint_16pp)png_calloc(png_ptr, num * (sizeof (png_uint_16p)));

       /* 'num' is the number of tables and also the number of low bits of low
        * bits of the input 16-bit value used to select a table.  Each table is
        * itself index by the high 8 bits of the value.
        */
       for (i = 0; i < num; i++)
          table[i] = (png_uint_16p)png_malloc(png_ptr,
              256 * (sizeof (png_uint_16)));

       /* 'gamma_val' is set to the reciprocal of the value calculated above, so
        * pow(out,g) is an *input* value.  'last' is the last input value set.
        *
        * In the loop 'i' is used to find output values.  Since the output is
        * 8-bit there are only 256 possible values.  The tables are set up to
        * select the closest possible output value for each input by finding
        * the input value at the boundary between each pair of output values
        * and filling the table up to that boundary with the lower output
        * value.
        *
        * The boundary values are 0.5,1.5..253.5,254.5.  Since these are 9-bit
        * values the code below uses a 16-bit value in i; the values start at
        * 128.5 (for 0.5) and step by 257, for a total of 254 values (the last
        * entries are filled with 255).  Start i at 128 and fill all 'last'
        * table entries <= 'max'
        */
       last = 0;
       for (i = 0; i < 255; ++i) /* 8-bit output value */
       {
          /* Find the corresponding maximum input value */
          png_uint_16 out = (png_uint_16)(i * 257U); /* 16-bit output value */

          /* Find the boundary value in 16 bits: */
          png_uint_32 bound = png_gamma_16bit_correct(out+128U, gamma_val);

          /* Adjust (round) to (16-shift) bits: */
          bound = (bound * max + 32768U)/65535U + 1U;

          while (last < bound)
          {
             table[last & (0xffU >> shift)][last >> (8U - shift)] = out;
             last++;
          }
       }

       /* And fill in the final entries. */
       while (last < (num << 8))
       {
          table[last & (0xff >> shift)][last >> (8U - shift)] = 65535U;
          last++;
       }
    }

    /* Build a single 8-bit table: same as the 16-bit case but much simpler (and
     * typically much faster).  Note that libpng currently does no sBIT processing
     * (apparently contrary to the spec) so a 256 entry table is always generated.
     */
    static void
    png_build_8bit_table(png_structrp png_ptr, png_bytepp ptable,
       PNG_CONST png_fixed_point gamma_val)
    {
       unsigned int i;
       png_bytep table = *ptable = (png_bytep)png_malloc(png_ptr, 256);

       if (png_gamma_significant(gamma_val)) for (i=0; i<256; i++)
          table[i] = png_gamma_8bit_correct(i, gamma_val);

       else for (i=0; i<256; ++i)
          table[i] = (png_byte)i;
    }

    /* Used from png_read_destroy and below to release the memory used by the gamma
     * tables.
     */
    void /* PRIVATE */
    png_destroy_gamma_table(png_structrp png_ptr)
    {
       png_free(png_ptr, png_ptr->gamma_table);
       png_ptr->gamma_table = NULL;

       if (png_ptr->gamma_16_table != NULL)
       {
          int i;
          int istop = (1 << (8 - png_ptr->gamma_shift));
          for (i = 0; i < istop; i++)
          {
             png_free(png_ptr, png_ptr->gamma_16_table[i]);
          }
       png_free(png_ptr, png_ptr->gamma_16_table);
       png_ptr->gamma_16_table = NULL;
       }

    #if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
       defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
       defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
       png_free(png_ptr, png_ptr->gamma_from_1);
       png_ptr->gamma_from_1 = NULL;
       png_free(png_ptr, png_ptr->gamma_to_1);
       png_ptr->gamma_to_1 = NULL;

       if (png_ptr->gamma_16_from_1 != NULL)
       {
          int i;
          int istop = (1 << (8 - png_ptr->gamma_shift));
          for (i = 0; i < istop; i++)
          {
             png_free(png_ptr, png_ptr->gamma_16_from_1[i]);
          }
       png_free(png_ptr, png_ptr->gamma_16_from_1);
       png_ptr->gamma_16_from_1 = NULL;
       }
       if (png_ptr->gamma_16_to_1 != NULL)
       {
          int i;
          int istop = (1 << (8 - png_ptr->gamma_shift));
          for (i = 0; i < istop; i++)
          {
             png_free(png_ptr, png_ptr->gamma_16_to_1[i]);
          }
       png_free(png_ptr, png_ptr->gamma_16_to_1);
       png_ptr->gamma_16_to_1 = NULL;
       }
    #endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
    }

    /* We build the 8- or 16-bit gamma tables here.  Note that for 16-bit
     * tables, we don't make a full table if we are reducing to 8-bit in
     * the future.  Note also how the gamma_16 tables are segmented so that
     * we don't need to allocate > 64K chunks for a full 16-bit table.
     */
    void /* PRIVATE */
    png_build_gamma_table(png_structrp png_ptr, int bit_depth)
    {
      png_debug(1, "in png_build_gamma_table");

      /* Remove any existing table; this copes with multiple calls to
       * png_read_update_info.  The warning is because building the gamma tables
       * multiple times is a performance hit - it's harmless but the ability to call
       * png_read_update_info() multiple times is new in 1.5.6 so it seems sensible
       * to warn if the app introduces such a hit.
       */
      if (png_ptr->gamma_table != NULL || png_ptr->gamma_16_table != NULL)
      {
        png_warning(png_ptr, "gamma table being rebuilt");
        png_destroy_gamma_table(png_ptr);
      }

      if (bit_depth <= 8)
      {
         png_build_8bit_table(png_ptr, &png_ptr->gamma_table,
             png_ptr->screen_gamma > 0 ?  png_reciprocal2(png_ptr->colorspace.gamma,
             png_ptr->screen_gamma) : PNG_FP_1);

    #if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
       defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
       defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
         if (png_ptr->transformations & (PNG_COMPOSE | PNG_RGB_TO_GRAY))
         {
            png_build_8bit_table(png_ptr, &png_ptr->gamma_to_1,
                png_reciprocal(png_ptr->colorspace.gamma));

            png_build_8bit_table(png_ptr, &png_ptr->gamma_from_1,
                png_ptr->screen_gamma > 0 ?  png_reciprocal(png_ptr->screen_gamma) :
                png_ptr->colorspace.gamma/* Probably doing rgb_to_gray */);
         }
    #endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
      }
      else
      {
         png_byte shift, sig_bit;

         if (png_ptr->color_type & PNG_COLOR_MASK_COLOR)
         {
            sig_bit = png_ptr->sig_bit.red;

            if (png_ptr->sig_bit.green > sig_bit)
               sig_bit = png_ptr->sig_bit.green;

            if (png_ptr->sig_bit.blue > sig_bit)
               sig_bit = png_ptr->sig_bit.blue;
         }
         else
            sig_bit = png_ptr->sig_bit.gray;

         /* 16-bit gamma code uses this equation:
          *
          *   ov = table[(iv & 0xff) >> gamma_shift][iv >> 8]
          *
          * Where 'iv' is the input color value and 'ov' is the output value -
          * pow(iv, gamma).
          *
          * Thus the gamma table consists of up to 256 256 entry tables.  The table
          * is selected by the (8-gamma_shift) most significant of the low 8 bits of
          * the color value then indexed by the upper 8 bits:
          *
          *   table[low bits][high 8 bits]
          *
          * So the table 'n' corresponds to all those 'iv' of:
          *
          *   <all high 8-bit values><n << gamma_shift>..<(n+1 << gamma_shift)-1>
          *
          */
         if (sig_bit > 0 && sig_bit < 16U)
            shift = (png_byte)(16U - sig_bit); /* shift == insignificant bits */

         else
            shift = 0; /* keep all 16 bits */

         if (png_ptr->transformations & (PNG_16_TO_8 | PNG_SCALE_16_TO_8))
         {
            /* PNG_MAX_GAMMA_8 is the number of bits to keep - effectively
             * the significant bits in the *input* when the output will
             * eventually be 8 bits.  By default it is 11.
             */
            if (shift < (16U - PNG_MAX_GAMMA_8))
               shift = (16U - PNG_MAX_GAMMA_8);
         }

         if (shift > 8U)
            shift = 8U; /* Guarantees at least one table! */

         png_ptr->gamma_shift = shift;

    #ifdef PNG_16BIT_SUPPORTED
         /* NOTE: prior to 1.5.4 this test used to include PNG_BACKGROUND (now
          * PNG_COMPOSE).  This effectively smashed the background calculation for
          * 16-bit output because the 8-bit table assumes the result will be reduced
          * to 8 bits.
          */
         if (png_ptr->transformations & (PNG_16_TO_8 | PNG_SCALE_16_TO_8))
    #endif
             png_build_16to8_table(png_ptr, &png_ptr->gamma_16_table, shift,
             png_ptr->screen_gamma > 0 ? png_product2(png_ptr->colorspace.gamma,
             png_ptr->screen_gamma) : PNG_FP_1);

    #ifdef PNG_16BIT_SUPPORTED
         else
             png_build_16bit_table(png_ptr, &png_ptr->gamma_16_table, shift,
             png_ptr->screen_gamma > 0 ? png_reciprocal2(png_ptr->colorspace.gamma,
             png_ptr->screen_gamma) : PNG_FP_1);
    #endif

    #if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
       defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
       defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
         if (png_ptr->transformations & (PNG_COMPOSE | PNG_RGB_TO_GRAY))
         {
            png_build_16bit_table(png_ptr, &png_ptr->gamma_16_to_1, shift,
                png_reciprocal(png_ptr->colorspace.gamma));

            /* Notice that the '16 from 1' table should be full precision, however
             * the lookup on this table still uses gamma_shift, so it can't be.
             * TODO: fix this.
             */
            png_build_16bit_table(png_ptr, &png_ptr->gamma_16_from_1, shift,
                png_ptr->screen_gamma > 0 ? png_reciprocal(png_ptr->screen_gamma) :
                png_ptr->colorspace.gamma/* Probably doing rgb_to_gray */);
         }
    #endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
      }
    }
    #endif /* READ_GAMMA */

    /* HARDWARE OPTION SUPPORT */
    #ifdef PNG_SET_OPTION_SUPPORTED
    int PNGAPI
    png_set_option(png_structrp png_ptr, int option, int onoff)
    {
       if (png_ptr != NULL && option >= 0 && option < PNG_OPTION_NEXT &&
          (option & 1) == 0)
       {
          int mask = 3 << option;
          int setting = (2 + (onoff != 0)) << option;
          int current = png_ptr->options;

          png_ptr->options = (png_byte)((current & ~mask) | setting);

          return (current & mask) >> option;
       }

       return PNG_OPTION_INVALID;
    }
    #endif

    /* sRGB support */
    #if defined(PNG_SIMPLIFIED_READ_SUPPORTED) ||\
       defined(PNG_SIMPLIFIED_WRITE_SUPPORTED)
    /* sRGB conversion tables; these are machine generated with the code in
     * contrib/tools/makesRGB.c.  The actual sRGB transfer curve defined in the
     * specification (see the article at http://en.wikipedia.org/wiki/SRGB)
     * is used, not the gamma=1/2.2 approximation use elsewhere in libpng.
     * The sRGB to linear table is exact (to the nearest 16 bit linear fraction).
     * The inverse (linear to sRGB) table has accuracies as follows:
     *
     * For all possible (255*65535+1) input values:
     *
     *    error: -0.515566 - 0.625971, 79441 (0.475369%) of readings inexact
     *
     * For the input values corresponding to the 65536 16-bit values:
     *
     *    error: -0.513727 - 0.607759, 308 (0.469978%) of readings inexact
     *
     * In all cases the inexact readings are off by one.
     */

    #ifdef PNG_SIMPLIFIED_READ_SUPPORTED
    /* The convert-to-sRGB table is only currently required for read. */
    const png_uint_16 png_sRGB_table[256] =
    {
       0,20,40,60,80,99,119,139,
       159,179,199,219,241,264,288,313,
       340,367,396,427,458,491,526,562,
       599,637,677,718,761,805,851,898,
       947,997,1048,1101,1156,1212,1270,1330,
       1391,1453,1517,1583,1651,1720,1790,1863,
       1937,2013,2090,2170,2250,2333,2418,2504,
       2592,2681,2773,2866,2961,3058,3157,3258,
       3360,3464,3570,3678,3788,3900,4014,4129,
       4247,4366,4488,4611,4736,4864,4993,5124,
       5257,5392,5530,5669,5810,5953,6099,6246,
       6395,6547,6700,6856,7014,7174,7335,7500,
       7666,7834,8004,8177,8352,8528,8708,8889,
       9072,9258,9445,9635,9828,10022,10219,10417,
       10619,10822,11028,11235,11446,11658,11873,12090,
       12309,12530,12754,12980,13209,13440,13673,13909,
       14146,14387,14629,14874,15122,15371,15623,15878,
       16135,16394,16656,16920,17187,17456,17727,18001,
       18277,18556,18837,19121,19407,19696,19987,20281,
       20577,20876,21177,21481,21787,22096,22407,22721,
       23038,23357,23678,24002,24329,24658,24990,25325,
       25662,26001,26344,26688,27036,27386,27739,28094,
       28452,28813,29176,29542,29911,30282,30656,31033,
       31412,31794,32179,32567,32957,33350,33745,34143,
       34544,34948,35355,35764,36176,36591,37008,37429,
       37852,38278,38706,39138,39572,40009,40449,40891,
       41337,41785,42236,42690,43147,43606,44069,44534,
       45002,45473,45947,46423,46903,47385,47871,48359,
       48850,49344,49841,50341,50844,51349,51858,52369,
       52884,53401,53921,54445,54971,55500,56032,56567,
       57105,57646,58190,58737,59287,59840,60396,60955,
       61517,62082,62650,63221,63795,64372,64952,65535
    };

    #endif /* simplified read only */

    /* The base/delta tables are required for both read and write (but currently
     * only the simplified versions.)
     */
    const png_uint_16 png_sRGB_base[512] =
    {
       128,1782,3383,4644,5675,6564,7357,8074,
       8732,9346,9921,10463,10977,11466,11935,12384,
       12816,13233,13634,14024,14402,14769,15125,15473,
       15812,16142,16466,16781,17090,17393,17690,17981,
       18266,18546,18822,19093,19359,19621,19879,20133,
       20383,20630,20873,21113,21349,21583,21813,22041,
       22265,22487,22707,22923,23138,23350,23559,23767,
       23972,24175,24376,24575,24772,24967,25160,25352,
       25542,25730,25916,26101,26284,26465,26645,26823,
       27000,27176,27350,27523,27695,27865,28034,28201,
       28368,28533,28697,28860,29021,29182,29341,29500,
       29657,29813,29969,30123,30276,30429,30580,30730,
       30880,31028,31176,31323,31469,31614,31758,31902,
       32045,32186,32327,32468,32607,32746,32884,33021,
       33158,33294,33429,33564,33697,33831,33963,34095,
       34226,34357,34486,34616,34744,34873,35000,35127,
       35253,35379,35504,35629,35753,35876,35999,36122,
       36244,36365,36486,36606,36726,36845,36964,37083,
       37201,37318,37435,37551,37668,37783,37898,38013,
       38127,38241,38354,38467,38580,38692,38803,38915,
       39026,39136,39246,39356,39465,39574,39682,39790,
       39898,40005,40112,40219,40325,40431,40537,40642,
       40747,40851,40955,41059,41163,41266,41369,41471,
       41573,41675,41777,41878,41979,42079,42179,42279,
       42379,42478,42577,42676,42775,42873,42971,43068,
       43165,43262,43359,43456,43552,43648,43743,43839,
       43934,44028,44123,44217,44311,44405,44499,44592,
       44685,44778,44870,44962,45054,45146,45238,45329,
       45420,45511,45601,45692,45782,45872,45961,46051,
       46140,46229,46318,46406,46494,46583,46670,46758,
       46846,46933,47020,47107,47193,47280,47366,47452,
       47538,47623,47709,47794,47879,47964,48048,48133,
       48217,48301,48385,48468,48552,48635,48718,48801,
       48884,48966,49048,49131,49213,49294,49376,49458,
       49539,49620,49701,49782,49862,49943,50023,50103,
       50183,50263,50342,50422,50501,50580,50659,50738,
       50816,50895,50973,51051,51129,51207,51285,51362,
       51439,51517,51594,51671,51747,51824,51900,51977,
       52053,52129,52205,52280,52356,52432,52507,52582,
       52657,52732,52807,52881,52956,53030,53104,53178,
       53252,53326,53400,53473,53546,53620,53693,53766,
       53839,53911,53984,54056,54129,54201,54273,54345,
       54417,54489,54560,54632,54703,54774,54845,54916,
       54987,55058,55129,55199,55269,55340,55410,55480,
       55550,55620,55689,55759,55828,55898,55967,56036,
       56105,56174,56243,56311,56380,56448,56517,56585,
       56653,56721,56789,56857,56924,56992,57059,57127,
       57194,57261,57328,57395,57462,57529,57595,57662,
       57728,57795,57861,57927,57993,58059,58125,58191,
       58256,58322,58387,58453,58518,58583,58648,58713,
       58778,58843,58908,58972,59037,59101,59165,59230,
       59294,59358,59422,59486,59549,59613,59677,59740,
       59804,59867,59930,59993,60056,60119,60182,60245,
       60308,60370,60433,60495,60558,60620,60682,60744,
       60806,60868,60930,60992,61054,61115,61177,61238,
       61300,61361,61422,61483,61544,61605,61666,61727,
       61788,61848,61909,61969,62030,62090,62150,62211,
       62271,62331,62391,62450,62510,62570,62630,62689,
       62749,62808,62867,62927,62986,63045,63104,63163,
       63222,63281,63340,63398,63457,63515,63574,63632,
       63691,63749,63807,63865,63923,63981,64039,64097,
       64155,64212,64270,64328,64385,64443,64500,64557,
       64614,64672,64729,64786,64843,64900,64956,65013,
       65070,65126,65183,65239,65296,65352,65409,65465
    };

    const png_byte png_sRGB_delta[512] =
    {
       207,201,158,129,113,100,90,82,77,72,68,64,61,59,56,54,
       52,50,49,47,46,45,43,42,41,40,39,39,38,37,36,36,
       35,34,34,33,33,32,32,31,31,30,30,30,29,29,28,28,
       28,27,27,27,27,26,26,26,25,25,25,25,24,24,24,24,
       23,23,23,23,23,22,22,22,22,22,22,21,21,21,21,21,
       21,20,20,20,20,20,20,20,20,19,19,19,19,19,19,19,
       19,18,18,18,18,18,18,18,18,18,18,17,17,17,17,17,
       17,17,17,17,17,17,16,16,16,16,16,16,16,16,16,16,
       16,16,16,16,15,15,15,15,15,15,15,15,15,15,15,15,
       15,15,15,15,14,14,14,14,14,14,14,14,14,14,14,14,
       14,14,14,14,14,14,14,13,13,13,13,13,13,13,13,13,
       13,13,13,13,13,13,13,13,13,13,13,13,13,13,12,12,
       12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,
       12,12,12,12,12,12,12,12,12,12,12,12,11,11,11,11,
       11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,
       11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,
       11,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,
       10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,
       10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,
       10,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
       9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
       9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
       9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
       9,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
       8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
       8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
       8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
       8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
       8,8,8,8,8,8,8,8,8,7,7,7,7,7,7,7,
       7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
       7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
       7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7
    };
    #endif /* SIMPLIFIED READ/WRITE sRGB support */

    /* SIMPLIFIED READ/WRITE SUPPORT */
    #if defined(PNG_SIMPLIFIED_READ_SUPPORTED) ||\
       defined(PNG_SIMPLIFIED_WRITE_SUPPORTED)
    static int
    png_image_free_function(png_voidp argument)
    {
       png_imagep image = png_voidcast(png_imagep, argument);
       png_controlp cp = image->opaque;
       png_control c;

       /* Double check that we have a png_ptr - it should be impossible to get here
        * without one.
        */
       if (cp->png_ptr == NULL)
          return 0;

       /* First free any data held in the control structure. */
    #  ifdef PNG_STDIO_SUPPORTED
          if (cp->owned_file)
          {
             FILE *fp = png_voidcast(FILE*, cp->png_ptr->io_ptr);
             cp->owned_file = 0;

             /* Ignore errors here. */
             if (fp != NULL)
             {
                cp->png_ptr->io_ptr = NULL;
                (void)fclose(fp);
             }
          }
    #  endif

       /* Copy the control structure so that the original, allocated, version can be
        * safely freed.  Notice that a png_error here stops the remainder of the
        * cleanup, but this is probably fine because that would indicate bad memory
        * problems anyway.
        */
       c = *cp;
       image->opaque = &c;
       png_free(c.png_ptr, cp);

       /* Then the structures, calling the correct API. */
       if (c.for_write)
       {
    #     ifdef PNG_SIMPLIFIED_WRITE_SUPPORTED
             png_destroy_write_struct(&c.png_ptr, &c.info_ptr);
    #     else
             png_error(c.png_ptr, "simplified write not supported");
    #     endif
       }
       else
       {
    #     ifdef PNG_SIMPLIFIED_READ_SUPPORTED
             png_destroy_read_struct(&c.png_ptr, &c.info_ptr, NULL);
    #     else
             png_error(c.png_ptr, "simplified read not supported");
    #     endif
       }

       /* Success. */
       return 1;
    }

    void PNGAPI
    png_image_free(png_imagep image)
    {
       /* Safely call the real function, but only if doing so is safe at this point
        * (if not inside an error handling context).  Otherwise assume
        * png_safe_execute will call this API after the return.
        */
       if (image != NULL && image->opaque != NULL &&
          image->opaque->error_buf == NULL)
       {
          /* Ignore errors here: */
          (void)png_safe_execute(image, png_image_free_function, image);
          image->opaque = NULL;
       }
    }

    int /* PRIVATE */
    png_image_error(png_imagep image, png_const_charp error_message)
    {
       /* Utility to log an error. */
       png_safecat(image->message, (sizeof image->message), 0, error_message);
       image->warning_or_error |= PNG_IMAGE_ERROR;
       png_image_free(image);
       return 0;
    }

    #endif /* SIMPLIFIED READ/WRITE */
    #endif /* defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) */