    /*
     * jmemmgr.c
     *
     * Copyright (C) 1991-1997, Thomas G. Lane.
     * This file is part of the Independent JPEG Group's software.
     * For conditions of distribution and use, see the accompanying README file.
     *
     * This file contains the JPEG system-independent memory management
     * routines.  This code is usable across a wide variety of machines; most
     * of the system dependencies have been isolated in a separate file.
     * The major functions provided here are:
     *   * pool-based allocation and freeing of memory;
     *   * policy decisions about how to divide available memory among the
     *     virtual arrays;
     *   * control logic for swapping virtual arrays between main memory and
     *     backing storage.
     * The separate system-dependent file provides the actual backing-storage
     * access code, and it contains the policy decision about how much total
     * main memory to use.
     * This file is system-dependent in the sense that some of its functions
     * are unnecessary in some systems.  For example, if there is enough virtual
     * memory so that backing storage will never be used, much of the virtual
     * array control logic could be removed.  (Of course, if you have that much
     * memory then you shouldn't care about a little bit of unused code...)
     */

    #define JPEG_INTERNALS
    #define AM_MEMORY_MANAGER	/* we define jvirt_Xarray_control structs */
    #include "jinclude.h"
    #include "jpeglib.h"
    #include "jmemsys.h"		/* import the system-dependent declarations */

    #ifndef NO_GETENV
    #ifndef HAVE_STDLIB_H		/* <stdlib.h> should declare getenv() */
    extern char * getenv JPP((const char * name));
    #endif
    #endif

    /*
     * Some important notes:
     *   The allocation routines provided here must never return NULL.
     *   They should exit to error_exit if unsuccessful.
     *
     *   It's not a good idea to try to merge the sarray and barray routines,
     *   even though they are textually almost the same, because samples are
     *   usually stored as bytes while coefficients are shorts or ints.  Thus,
     *   in machines where byte pointers have a different representation from
     *   word pointers, the resulting machine code could not be the same.
     */

    /*
     * Many machines require storage alignment: longs must start on 4-byte
     * boundaries, doubles on 8-byte boundaries, etc.  On such machines, malloc()
     * always returns pointers that are multiples of the worst-case alignment
     * requirement, and we had better do so too.
     * There isn't any really portable way to determine the worst-case alignment
     * requirement.  This module assumes that the alignment requirement is
     * multiples of sizeof(ALIGN_TYPE).
     * By default, we define ALIGN_TYPE as double.  This is necessary on some
     * workstations (where doubles really do need 8-byte alignment) and will work
     * fine on nearly everything.  If your machine has lesser alignment needs,
     * you can save a few bytes by making ALIGN_TYPE smaller.
     * The only place I know of where this will NOT work is certain Macintosh
     * 680x0 compilers that define double as a 10-byte IEEE extended float.
     * Doing 10-byte alignment is counterproductive because longwords won't be
     * aligned well.  Put "#define ALIGN_TYPE long" in jconfig.h if you have
     * such a compiler.
     */

    #ifndef ALIGN_TYPE		/* so can override from jconfig.h */
    #define ALIGN_TYPE  double
    #endif

    /*
     * We allocate objects from "pools", where each pool is gotten with a single
     * request to jpeg_get_small() or jpeg_get_large().  There is no per-object
     * overhead within a pool, except for alignment padding.  Each pool has a
     * header with a link to the next pool of the same class.
     * Small and large pool headers are identical except that the latter's
     * link pointer must be FAR on 80x86 machines.
     * Notice that the "real" header fields are union'ed with a dummy ALIGN_TYPE
     * field.  This forces the compiler to make SIZEOF(small_pool_hdr) a multiple
     * of the alignment requirement of ALIGN_TYPE.
     */

    typedef union small_pool_struct * small_pool_ptr;

    typedef union small_pool_struct {
      struct {
        small_pool_ptr next;	/* next in list of pools */
        size_t bytes_used;		/* how many bytes already used within pool */
        size_t bytes_left;		/* bytes still available in this pool */
      } hdr;
      ALIGN_TYPE dummy;		/* included in union to ensure alignment */
    } small_pool_hdr;

    typedef union large_pool_struct FAR * large_pool_ptr;

    typedef union large_pool_struct {
      struct {
        large_pool_ptr next;	/* next in list of pools */
        size_t bytes_used;		/* how many bytes already used within pool */
        size_t bytes_left;		/* bytes still available in this pool */
      } hdr;
      ALIGN_TYPE dummy;		/* included in union to ensure alignment */
    } large_pool_hdr;

    /*
     * Here is the full definition of a memory manager object.
     */

    typedef struct {
      struct jpeg_memory_mgr pub;	/* public fields */

      /* Each pool identifier (lifetime class) names a linked list of pools. */
      small_pool_ptr small_list[JPOOL_NUMPOOLS];
      large_pool_ptr large_list[JPOOL_NUMPOOLS];

      /* Since we only have one lifetime class of virtual arrays, only one
       * linked list is necessary (for each datatype).  Note that the virtual
       * array control blocks being linked together are actually stored somewhere
       * in the small-pool list.
       */
      jvirt_sarray_ptr virt_sarray_list;
      jvirt_barray_ptr virt_barray_list;

      /* This counts total space obtained from jpeg_get_small/large */
      long total_space_allocated;

      /* alloc_sarray and alloc_barray set this value for use by virtual
       * array routines.
       */
      JDIMENSION last_rowsperchunk;	/* from most recent alloc_sarray/barray */
    } my_memory_mgr;

    typedef my_memory_mgr * my_mem_ptr;

    /*
     * The control blocks for virtual arrays.
     * Note that these blocks are allocated in the "small" pool area.
     * System-dependent info for the associated backing store (if any) is hidden
     * inside the backing_store_info struct.
     */

    struct jvirt_sarray_control {
      JSAMPARRAY mem_buffer;	/* => the in-memory buffer */
      JDIMENSION rows_in_array;	/* total virtual array height */
      JDIMENSION samplesperrow;	/* width of array (and of memory buffer) */
      JDIMENSION maxaccess;		/* max rows accessed by access_virt_sarray */
      JDIMENSION rows_in_mem;	/* height of memory buffer */
      JDIMENSION rowsperchunk;	/* allocation chunk size in mem_buffer */
      JDIMENSION cur_start_row;	/* first logical row # in the buffer */
      JDIMENSION first_undef_row;	/* row # of first uninitialized row */
      int pre_zero;		/* pre-zero mode requested? */
      int dirty;		/* do current buffer contents need written? */
      int b_s_open;		/* is backing-store data valid? */
      jvirt_sarray_ptr next;	/* link to next virtual sarray control block */
      backing_store_info b_s_info;	/* System-dependent control info */
    };

    struct jvirt_barray_control {
      JBLOCKARRAY mem_buffer;	/* => the in-memory buffer */
      JDIMENSION rows_in_array;	/* total virtual array height */
      JDIMENSION blocksperrow;	/* width of array (and of memory buffer) */
      JDIMENSION maxaccess;		/* max rows accessed by access_virt_barray */
      JDIMENSION rows_in_mem;	/* height of memory buffer */
      JDIMENSION rowsperchunk;	/* allocation chunk size in mem_buffer */
      JDIMENSION cur_start_row;	/* first logical row # in the buffer */
      JDIMENSION first_undef_row;	/* row # of first uninitialized row */
      int pre_zero;		/* pre-zero mode requested? */
      int dirty;		/* do current buffer contents need written? */
      int b_s_open;		/* is backing-store data valid? */
      jvirt_barray_ptr next;	/* link to next virtual barray control block */
      backing_store_info b_s_info;	/* System-dependent control info */
    };

    #ifdef MEM_STATS		/* optional extra stuff for statistics */

    LOCAL(void)
    print_mem_stats (j_common_ptr cinfo, int pool_id)
    {
      my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
      small_pool_ptr shdr_ptr;
      large_pool_ptr lhdr_ptr;

      /* Since this is only a debugging stub, we can cheat a little by using
       * fprintf directly rather than going through the trace message code.
       * This is helpful because message parm array can't handle longs.
       */
      fprintf(stderr, "Freeing pool %d, total space = %ld\n",
    	  pool_id, mem->total_space_allocated);

      for (lhdr_ptr = mem->large_list[pool_id]; lhdr_ptr != NULL;
           lhdr_ptr = lhdr_ptr->hdr.next) {
        fprintf(stderr, "  Large chunk used %ld\n",
    	    (long) lhdr_ptr->hdr.bytes_used);
      }

      for (shdr_ptr = mem->small_list[pool_id]; shdr_ptr != NULL;
           shdr_ptr = shdr_ptr->hdr.next) {
        fprintf(stderr, "  Small chunk used %ld free %ld\n",
    	    (long) shdr_ptr->hdr.bytes_used,
    	    (long) shdr_ptr->hdr.bytes_left);
      }
    }

    #endif /* MEM_STATS */

    LOCAL(void)
    out_of_memory (j_common_ptr cinfo, int which)
    /* Report an out-of-memory error and stop execution */
    /* If we compiled MEM_STATS support, report alloc requests before dying */
    {
    #ifdef MEM_STATS
      cinfo->err->trace_level = 2;	/* force self_destruct to report stats */
    #endif
      ERREXIT1(cinfo, JERR_OUT_OF_MEMORY, which);
    }

    /*
     * Allocation of "small" objects.
     *
     * For these, we use pooled storage.  When a new pool must be created,
     * we try to get enough space for the current request plus a "slop" factor,
     * where the slop will be the amount of leftover space in the new pool.
     * The speed vs. space tradeoff is largely determined by the slop values.
     * A different slop value is provided for each pool class (lifetime),
     * and we also distinguish the first pool of a class from later ones.
     * NOTE: the values given work fairly well on both 16- and 32-bit-int
     * machines, but may be too small if longs are 64 bits or more.
     */

    static const size_t first_pool_slop[JPOOL_NUMPOOLS] =
    {
    	1600,			/* first PERMANENT pool */
    	16000			/* first IMAGE pool */
    };

    static const size_t extra_pool_slop[JPOOL_NUMPOOLS] =
    {
    	0,			/* additional PERMANENT pools */
    	5000			/* additional IMAGE pools */
    };

    #define MIN_SLOP  50		/* greater than 0 to avoid futile looping */

    METHODDEF(void *)
    alloc_small (j_common_ptr cinfo, int pool_id, size_t sizeofobject)
    /* Allocate a "small" object */
    {
      my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
      small_pool_ptr hdr_ptr, prev_hdr_ptr;
      char * data_ptr;
      size_t odd_bytes, min_request, slop;

      /* Check for unsatisfiable request (do now to ensure no overflow below) */
      if (sizeofobject > (size_t) (MAX_ALLOC_CHUNK-SIZEOF(small_pool_hdr)))
        out_of_memory(cinfo, 1);	/* request exceeds malloc's ability */

      /* Round up the requested size to a multiple of SIZEOF(ALIGN_TYPE) */
      odd_bytes = sizeofobject % SIZEOF(ALIGN_TYPE);
      if (odd_bytes > 0)
        sizeofobject += SIZEOF(ALIGN_TYPE) - odd_bytes;

      /* See if space is available in any existing pool */
      if (pool_id < 0 || pool_id >= JPOOL_NUMPOOLS)
        ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */
      prev_hdr_ptr = NULL;
      hdr_ptr = mem->small_list[pool_id];
      while (hdr_ptr != NULL) {
        if (hdr_ptr->hdr.bytes_left >= sizeofobject)
          break;			/* found pool with enough space */
        prev_hdr_ptr = hdr_ptr;
        hdr_ptr = hdr_ptr->hdr.next;
      }

      /* Time to make a new pool? */
      if (hdr_ptr == NULL) {
        /* min_request is what we need now, slop is what will be leftover */
        min_request = sizeofobject + SIZEOF(small_pool_hdr);
        if (prev_hdr_ptr == NULL)	/* first pool in class? */
          slop = first_pool_slop[pool_id];
        else
          slop = extra_pool_slop[pool_id];
        /* Don't ask for more than MAX_ALLOC_CHUNK */
        if (slop > (size_t) (MAX_ALLOC_CHUNK-min_request))
          slop = (size_t) (MAX_ALLOC_CHUNK-min_request);
        /* Try to get space, if fail reduce slop and try again */
        for (;;) {
          hdr_ptr = (small_pool_ptr) jpeg_get_small(cinfo, min_request + slop);
          if (hdr_ptr != NULL)
    	break;
          slop /= 2;
          if (slop < MIN_SLOP)	/* give up when it gets real small */
    	out_of_memory(cinfo, 2); /* jpeg_get_small failed */
        }
        mem->total_space_allocated += (long)(min_request + slop);
        /* Success, initialize the new pool header and add to end of list */
        hdr_ptr->hdr.next = NULL;
        hdr_ptr->hdr.bytes_used = 0;
        hdr_ptr->hdr.bytes_left = sizeofobject + slop;
        if (prev_hdr_ptr == NULL)	/* first pool in class? */
          mem->small_list[pool_id] = hdr_ptr;
        else
          prev_hdr_ptr->hdr.next = hdr_ptr;
      }

      /* OK, allocate the object from the current pool */
      data_ptr = (char *) (hdr_ptr + 1); /* point to first data byte in pool */
      data_ptr += hdr_ptr->hdr.bytes_used; /* point to place for object */
      hdr_ptr->hdr.bytes_used += sizeofobject;
      hdr_ptr->hdr.bytes_left -= sizeofobject;

      return (void *) data_ptr;
    }

    /*
     * Allocation of "large" objects.
     *
     * The external semantics of these are the same as "small" objects,
     * except that FAR pointers are used on 80x86.  However the pool
     * management heuristics are quite different.  We assume that each
     * request is large enough that it may as well be passed directly to
     * jpeg_get_large; the pool management just links everything together
     * so that we can free it all on demand.
     * Note: the major use of "large" objects is in JSAMPARRAY and JBLOCKARRAY
     * structures.  The routines that create these structures (see below)
     * deliberately bunch rows together to ensure a large request size.
     */

    METHODDEF(void FAR *)
    alloc_large (j_common_ptr cinfo, int pool_id, size_t sizeofobject)
    /* Allocate a "large" object */
    {
      my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
      large_pool_ptr hdr_ptr;
      size_t odd_bytes;

      /* Check for unsatisfiable request (do now to ensure no overflow below) */
      if (sizeofobject > (size_t) (MAX_ALLOC_CHUNK-SIZEOF(large_pool_hdr)))
        out_of_memory(cinfo, 3);	/* request exceeds malloc's ability */

      /* Round up the requested size to a multiple of SIZEOF(ALIGN_TYPE) */
      odd_bytes = sizeofobject % SIZEOF(ALIGN_TYPE);
      if (odd_bytes > 0)
        sizeofobject += SIZEOF(ALIGN_TYPE) - odd_bytes;

      /* Always make a new pool */
      if (pool_id < 0 || pool_id >= JPOOL_NUMPOOLS)
        ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */

      hdr_ptr = (large_pool_ptr) jpeg_get_large(cinfo, sizeofobject +
    					    SIZEOF(large_pool_hdr));
      if (hdr_ptr == NULL)
        out_of_memory(cinfo, 4);	/* jpeg_get_large failed */
      mem->total_space_allocated += (long)(sizeofobject + SIZEOF(large_pool_hdr));

      /* Success, initialize the new pool header and add to list */
      hdr_ptr->hdr.next = mem->large_list[pool_id];
      /* We maintain space counts in each pool header for statistical purposes,
       * even though they are not needed for allocation.
       */
      hdr_ptr->hdr.bytes_used = sizeofobject;
      hdr_ptr->hdr.bytes_left = 0;
      mem->large_list[pool_id] = hdr_ptr;

      return (void FAR *) (hdr_ptr + 1); /* point to first data byte in pool */
    }

    /*
     * Creation of 2-D sample arrays.
     * The pointers are in near heap, the samples themselves in FAR heap.
     *
     * To minimize allocation overhead and to allow I/O of large contiguous
     * blocks, we allocate the sample rows in groups of as many rows as possible
     * without exceeding MAX_ALLOC_CHUNK total bytes per allocation request.
     * NB: the virtual array control routines, later in this file, know about
     * this chunking of rows.  The rowsperchunk value is left in the mem manager
     * object so that it can be saved away if this sarray is the workspace for
     * a virtual array.
     */

    METHODDEF(JSAMPARRAY)
    alloc_sarray (j_common_ptr cinfo, int pool_id,
    	      JDIMENSION samplesperrow, JDIMENSION numrows)
    /* Allocate a 2-D sample array */
    {
      my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
      JSAMPARRAY result;
      JSAMPROW workspace;
      JDIMENSION rowsperchunk, currow, i;
      long ltemp;

      /* Calculate max # of rows allowed in one allocation chunk */
      ltemp = (MAX_ALLOC_CHUNK-SIZEOF(large_pool_hdr)) /
    	  ((long) samplesperrow * SIZEOF(JSAMPLE));
      if (ltemp <= 0)
        ERREXIT(cinfo, JERR_WIDTH_OVERFLOW);
      if (ltemp < (long) numrows)
        rowsperchunk = (JDIMENSION) ltemp;
      else
        rowsperchunk = numrows;
      mem->last_rowsperchunk = rowsperchunk;

      /* Get space for row pointers (small object) */
      result = (JSAMPARRAY) alloc_small(cinfo, pool_id,
    				    (size_t) (numrows * SIZEOF(JSAMPROW)));

      /* Get the rows themselves (large objects) */
      currow = 0;
      while (currow < numrows) {
        rowsperchunk = MIN(rowsperchunk, numrows - currow);
        workspace = (JSAMPROW) alloc_large(cinfo, pool_id,
    	(size_t) ((size_t) rowsperchunk * (size_t) samplesperrow
    		  * SIZEOF(JSAMPLE)));
        for (i = rowsperchunk; i > 0; i--) {
          result[currow++] = workspace;
          workspace += samplesperrow;
        }
      }

      return result;
    }

    /*
     * Creation of 2-D coefficient-block arrays.
     * This is essentially the same as the code for sample arrays, above.
     */

    METHODDEF(JBLOCKARRAY)
    alloc_barray (j_common_ptr cinfo, int pool_id,
    	      JDIMENSION blocksperrow, JDIMENSION numrows)
    /* Allocate a 2-D coefficient-block array */
    {
      my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
      JBLOCKARRAY result;
      JBLOCKROW workspace;
      JDIMENSION rowsperchunk, currow, i;
      long ltemp;

      /* Calculate max # of rows allowed in one allocation chunk */
      ltemp = (MAX_ALLOC_CHUNK-SIZEOF(large_pool_hdr)) /
    	  ((long) blocksperrow * SIZEOF(JBLOCK));
      if (ltemp <= 0)
        ERREXIT(cinfo, JERR_WIDTH_OVERFLOW);
      if (ltemp < (long) numrows)
        rowsperchunk = (JDIMENSION) ltemp;
      else
        rowsperchunk = numrows;
      mem->last_rowsperchunk = rowsperchunk;

      /* Get space for row pointers (small object) */
      result = (JBLOCKARRAY) alloc_small(cinfo, pool_id,
    				     (size_t) (numrows * SIZEOF(JBLOCKROW)));

      /* Get the rows themselves (large objects) */
      currow = 0;
      while (currow < numrows) {
        rowsperchunk = MIN(rowsperchunk, numrows - currow);
        workspace = (JBLOCKROW) alloc_large(cinfo, pool_id,
    	(size_t) ((size_t) rowsperchunk * (size_t) blocksperrow
    		  * SIZEOF(JBLOCK)));
        for (i = rowsperchunk; i > 0; i--) {
          result[currow++] = workspace;
          workspace += blocksperrow;
        }
      }

      return result;
    }

    /*
     * About virtual array management:
     *
     * The above "normal" array routines are only used to allocate strip buffers
     * (as wide as the image, but just a few rows high).  Full-image-sized buffers
     * are handled as "virtual" arrays.  The array is still accessed a strip at a
     * time, but the memory manager must save the whole array for repeated
     * accesses.  The intended implementation is that there is a strip buffer in
     * memory (as high as is possible given the desired memory limit), plus a
     * backing file that holds the rest of the array.
     *
     * The request_virt_array routines are told the total size of the image and
     * the maximum number of rows that will be accessed at once.  The in-memory
     * buffer must be at least as large as the maxaccess value.
     *
     * The request routines create control blocks but not the in-memory buffers.
     * That is postponed until realize_virt_arrays is called.  At that time the
     * total amount of space needed is known (approximately, anyway), so free
     * memory can be divided up fairly.
     *
     * The access_virt_array routines are responsible for making a specific strip
     * area accessible (after reading or writing the backing file, if necessary).
     * Note that the access routines are told whether the caller intends to modify
     * the accessed strip; during a read-only pass this saves having to rewrite
     * data to disk.  The access routines are also responsible for pre-zeroing
     * any newly accessed rows, if pre-zeroing was requested.
     *
     * In current usage, the access requests are usually for nonoverlapping
     * strips; that is, successive access start_row numbers differ by exactly
     * num_rows = maxaccess.  This means we can get good performance with simple
     * buffer dump/reload logic, by making the in-memory buffer be a multiple
     * of the access height; then there will never be accesses across bufferload
     * boundaries.  The code will still work with overlapping access requests,
     * but it doesn't handle bufferload overlaps very efficiently.
     */

    METHODDEF(jvirt_sarray_ptr)
    request_virt_sarray (j_common_ptr cinfo, int pool_id, int pre_zero,
    		     JDIMENSION samplesperrow, JDIMENSION numrows,
    		     JDIMENSION maxaccess)
    /* Request a virtual 2-D sample array */
    {
      my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
      jvirt_sarray_ptr result;

      /* Only IMAGE-lifetime virtual arrays are currently supported */
      if (pool_id != JPOOL_IMAGE)
        ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */

      /* get control block */
      result = (jvirt_sarray_ptr) alloc_small(cinfo, pool_id,
    					  SIZEOF(struct jvirt_sarray_control));

      result->mem_buffer = NULL;	/* marks array not yet realized */
      result->rows_in_array = numrows;
      result->samplesperrow = samplesperrow;
      result->maxaccess = maxaccess;
      result->pre_zero = pre_zero;
      result->b_s_open = FALSE;	/* no associated backing-store object */
      result->next = mem->virt_sarray_list; /* add to list of virtual arrays */
      mem->virt_sarray_list = result;

      return result;
    }

    METHODDEF(jvirt_barray_ptr)
    request_virt_barray (j_common_ptr cinfo, int pool_id, int pre_zero,
    		     JDIMENSION blocksperrow, JDIMENSION numrows,
    		     JDIMENSION maxaccess)
    /* Request a virtual 2-D coefficient-block array */
    {
      my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
      jvirt_barray_ptr result;

      /* Only IMAGE-lifetime virtual arrays are currently supported */
      if (pool_id != JPOOL_IMAGE)
        ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */

      /* get control block */
      result = (jvirt_barray_ptr) alloc_small(cinfo, pool_id,
    					  SIZEOF(struct jvirt_barray_control));

      result->mem_buffer = NULL;	/* marks array not yet realized */
      result->rows_in_array = numrows;
      result->blocksperrow = blocksperrow;
      result->maxaccess = maxaccess;
      result->pre_zero = pre_zero;
      result->b_s_open = FALSE;	/* no associated backing-store object */
      result->next = mem->virt_barray_list; /* add to list of virtual arrays */
      mem->virt_barray_list = result;

      return result;
    }

    METHODDEF(void)
    realize_virt_arrays (j_common_ptr cinfo)
    /* Allocate the in-memory buffers for any unrealized virtual arrays */
    {
      my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
      long space_per_minheight, maximum_space, avail_mem;
      long minheights, max_minheights;
      jvirt_sarray_ptr sptr;
      jvirt_barray_ptr bptr;

      /* Compute the minimum space needed (maxaccess rows in each buffer)
       * and the maximum space needed (full image height in each buffer).
       * These may be of use to the system-dependent jpeg_mem_available routine.
       */
      space_per_minheight = 0;
      maximum_space = 0;
      for (sptr = mem->virt_sarray_list; sptr != NULL; sptr = sptr->next) {
        if (sptr->mem_buffer == NULL) { /* if not realized yet */
          space_per_minheight += (long) sptr->maxaccess *
    			     (long) sptr->samplesperrow * SIZEOF(JSAMPLE);
          maximum_space += (long) sptr->rows_in_array *
    		       (long) sptr->samplesperrow * SIZEOF(JSAMPLE);
        }
      }
      for (bptr = mem->virt_barray_list; bptr != NULL; bptr = bptr->next) {
        if (bptr->mem_buffer == NULL) { /* if not realized yet */
          space_per_minheight += (long) bptr->maxaccess *
    			     (long) bptr->blocksperrow * SIZEOF(JBLOCK);
          maximum_space += (long) bptr->rows_in_array *
    		       (long) bptr->blocksperrow * SIZEOF(JBLOCK);
        }
      }

      if (space_per_minheight <= 0)
        return;			/* no unrealized arrays, no work */

      /* Determine amount of memory to actually use; this is system-dependent. */
      avail_mem = jpeg_mem_available(cinfo, space_per_minheight, maximum_space,
    				 mem->total_space_allocated);

      /* If the maximum space needed is available, make all the buffers full
       * height; otherwise parcel it out with the same number of minheights
       * in each buffer.
       */
      if (avail_mem >= maximum_space)
        max_minheights = 1000000000L;
      else {
        max_minheights = avail_mem / space_per_minheight;
        /* If there doesn't seem to be enough space, try to get the minimum
         * anyway.  This allows a "stub" implementation of jpeg_mem_available().
         */
        if (max_minheights <= 0)
          max_minheights = 1;
      }

      /* Allocate the in-memory buffers and initialize backing store as needed. */

      for (sptr = mem->virt_sarray_list; sptr != NULL; sptr = sptr->next) {
        if (sptr->mem_buffer == NULL) { /* if not realized yet */
          minheights = ((long) sptr->rows_in_array - 1L) / sptr->maxaccess + 1L;
          if (minheights <= max_minheights) {
    	/* This buffer fits in memory */
    	sptr->rows_in_mem = sptr->rows_in_array;
          } else {
    	/* It doesn't fit in memory, create backing store. */
    	sptr->rows_in_mem = (JDIMENSION) (max_minheights * sptr->maxaccess);
    	jpeg_open_backing_store(cinfo, & sptr->b_s_info,
    				(long) sptr->rows_in_array *
    				(long) sptr->samplesperrow *
    				(long) SIZEOF(JSAMPLE));
    	sptr->b_s_open = TRUE;
          }
          sptr->mem_buffer = alloc_sarray(cinfo, JPOOL_IMAGE,
    				      sptr->samplesperrow, sptr->rows_in_mem);
          sptr->rowsperchunk = mem->last_rowsperchunk;
          sptr->cur_start_row = 0;
          sptr->first_undef_row = 0;
          sptr->dirty = FALSE;
        }
      }

      for (bptr = mem->virt_barray_list; bptr != NULL; bptr = bptr->next) {
        if (bptr->mem_buffer == NULL) { /* if not realized yet */
          minheights = ((long) bptr->rows_in_array - 1L) / bptr->maxaccess + 1L;
          if (minheights <= max_minheights) {
    	/* This buffer fits in memory */
    	bptr->rows_in_mem = bptr->rows_in_array;
          } else {
    	/* It doesn't fit in memory, create backing store. */
    	bptr->rows_in_mem = (JDIMENSION) (max_minheights * bptr->maxaccess);
    	jpeg_open_backing_store(cinfo, & bptr->b_s_info,
    				(long) bptr->rows_in_array *
    				(long) bptr->blocksperrow *
    				(long) SIZEOF(JBLOCK));
    	bptr->b_s_open = TRUE;
          }
          bptr->mem_buffer = alloc_barray(cinfo, JPOOL_IMAGE,
    				      bptr->blocksperrow, bptr->rows_in_mem);
          bptr->rowsperchunk = mem->last_rowsperchunk;
          bptr->cur_start_row = 0;
          bptr->first_undef_row = 0;
          bptr->dirty = FALSE;
        }
      }
    }

    LOCAL(void)
    do_sarray_io (j_common_ptr cinfo, jvirt_sarray_ptr ptr, int writing)
    /* Do backing store read or write of a virtual sample array */
    {
      long bytesperrow, file_offset, byte_count, rows, thisrow, i;

      bytesperrow = (long) ptr->samplesperrow * SIZEOF(JSAMPLE);
      file_offset = ptr->cur_start_row * bytesperrow;
      /* Loop to read or write each allocation chunk in mem_buffer */
      for (i = 0; i < (long) ptr->rows_in_mem; i += ptr->rowsperchunk) {
        /* One chunk, but check for short chunk at end of buffer */
        rows = MIN((long) ptr->rowsperchunk, (long) ptr->rows_in_mem - i);
        /* Transfer no more than is currently defined */
        thisrow = (long) ptr->cur_start_row + i;
        rows = MIN(rows, (long) ptr->first_undef_row - thisrow);
        /* Transfer no more than fits in file */
        rows = MIN(rows, (long) ptr->rows_in_array - thisrow);
        if (rows <= 0)		/* this chunk might be past end of file! */
          break;
        byte_count = rows * bytesperrow;
        if (writing)
          (*ptr->b_s_info.write_backing_store) (cinfo, & ptr->b_s_info,
    					    (void FAR *) ptr->mem_buffer[i],
    					    file_offset, byte_count);
        else
          (*ptr->b_s_info.read_backing_store) (cinfo, & ptr->b_s_info,
    					   (void FAR *) ptr->mem_buffer[i],
    					   file_offset, byte_count);
        file_offset += byte_count;
      }
    }

    LOCAL(void)
    do_barray_io (j_common_ptr cinfo, jvirt_barray_ptr ptr, int writing)
    /* Do backing store read or write of a virtual coefficient-block array */
    {
      long bytesperrow, file_offset, byte_count, rows, thisrow, i;

      bytesperrow = (long) ptr->blocksperrow * SIZEOF(JBLOCK);
      file_offset = ptr->cur_start_row * bytesperrow;
      /* Loop to read or write each allocation chunk in mem_buffer */
      for (i = 0; i < (long) ptr->rows_in_mem; i += ptr->rowsperchunk) {
        /* One chunk, but check for short chunk at end of buffer */
        rows = MIN((long) ptr->rowsperchunk, (long) ptr->rows_in_mem - i);
        /* Transfer no more than is currently defined */
        thisrow = (long) ptr->cur_start_row + i;
        rows = MIN(rows, (long) ptr->first_undef_row - thisrow);
        /* Transfer no more than fits in file */
        rows = MIN(rows, (long) ptr->rows_in_array - thisrow);
        if (rows <= 0)		/* this chunk might be past end of file! */
          break;
        byte_count = rows * bytesperrow;
        if (writing)
          (*ptr->b_s_info.write_backing_store) (cinfo, & ptr->b_s_info,
    					    (void FAR *) ptr->mem_buffer[i],
    					    file_offset, byte_count);
        else
          (*ptr->b_s_info.read_backing_store) (cinfo, & ptr->b_s_info,
    					   (void FAR *) ptr->mem_buffer[i],
    					   file_offset, byte_count);
        file_offset += byte_count;
      }
    }

    METHODDEF(JSAMPARRAY)
    access_virt_sarray (j_common_ptr cinfo, jvirt_sarray_ptr ptr,
    		    JDIMENSION start_row, JDIMENSION num_rows,
    		    int writable)
    /* Access the part of a virtual sample array starting at start_row */
    /* and extending for num_rows rows.  writable is true if  */
    /* caller intends to modify the accessed area. */
    {
      JDIMENSION end_row = start_row + num_rows;
      JDIMENSION undef_row;

      /* debugging check */
      if (end_row > ptr->rows_in_array || num_rows > ptr->maxaccess ||
          ptr->mem_buffer == NULL)
        ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);

      /* Make the desired part of the virtual array accessible */
      if (start_row < ptr->cur_start_row ||
          end_row > ptr->cur_start_row+ptr->rows_in_mem) {
        if (! ptr->b_s_open)
          ERREXIT(cinfo, JERR_VIRTUAL_BUG);
        /* Flush old buffer contents if necessary */
        if (ptr->dirty) {
          do_sarray_io(cinfo, ptr, TRUE);
          ptr->dirty = FALSE;
        }
        /* Decide what part of virtual array to access.
         * Algorithm: if target address > current window, assume forward scan,
         * load starting at target address.  If target address < current window,
         * assume backward scan, load so that target area is top of window.
         * Note that when switching from forward write to forward read, will have
         * start_row = 0, so the limiting case applies and we load from 0 anyway.
         */
        if (start_row > ptr->cur_start_row) {
          ptr->cur_start_row = start_row;
        } else {
          /* use long arithmetic here to avoid overflow & unsigned problems */
          long ltemp;

          ltemp = (long) end_row - (long) ptr->rows_in_mem;
          if (ltemp < 0)
    	ltemp = 0;		/* don't fall off front end of file */
          ptr->cur_start_row = (JDIMENSION) ltemp;
        }
        /* Read in the selected part of the array.
         * During the initial write pass, we will do no actual read
         * because the selected part is all undefined.
         */
        do_sarray_io(cinfo, ptr, FALSE);
      }
      /* Ensure the accessed part of the array is defined; prezero if needed.
       * To improve locality of access, we only prezero the part of the array
       * that the caller is about to access, not the entire in-memory array.
       */
      if (ptr->first_undef_row < end_row) {
        if (ptr->first_undef_row < start_row) {
          if (writable)		/* writer skipped over a section of array */
    	ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);
          undef_row = start_row;	/* but reader is allowed to read ahead */
        } else {
          undef_row = ptr->first_undef_row;
        }
        if (writable)
          ptr->first_undef_row = end_row;
        if (ptr->pre_zero) {
          size_t bytesperrow = (size_t) ptr->samplesperrow * SIZEOF(JSAMPLE);
          undef_row -= ptr->cur_start_row; /* make indexes relative to buffer */
          end_row -= ptr->cur_start_row;
          while (undef_row < end_row) {
    	jzero_far((void FAR *) ptr->mem_buffer[undef_row], bytesperrow);
    	undef_row++;
          }
        } else {
          if (! writable)		/* reader looking at undefined data */
    	ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);
        }
      }
      /* Flag the buffer dirty if caller will write in it */
      if (writable)
        ptr->dirty = TRUE;
      /* Return address of proper part of the buffer */
      return ptr->mem_buffer + (start_row - ptr->cur_start_row);
    }

    METHODDEF(JBLOCKARRAY)
    access_virt_barray (j_common_ptr cinfo, jvirt_barray_ptr ptr,
    		    JDIMENSION start_row, JDIMENSION num_rows,
    		    int writable)
    /* Access the part of a virtual block array starting at start_row */
    /* and extending for num_rows rows.  writable is true if  */
    /* caller intends to modify the accessed area. */
    {
      JDIMENSION end_row = start_row + num_rows;
      JDIMENSION undef_row;

      /* debugging check */
      if (end_row > ptr->rows_in_array || num_rows > ptr->maxaccess ||
          ptr->mem_buffer == NULL)
        ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);

      /* Make the desired part of the virtual array accessible */
      if (start_row < ptr->cur_start_row ||
          end_row > ptr->cur_start_row+ptr->rows_in_mem) {
        if (! ptr->b_s_open)
          ERREXIT(cinfo, JERR_VIRTUAL_BUG);
        /* Flush old buffer contents if necessary */
        if (ptr->dirty) {
          do_barray_io(cinfo, ptr, TRUE);
          ptr->dirty = FALSE;
        }
        /* Decide what part of virtual array to access.
         * Algorithm: if target address > current window, assume forward scan,
         * load starting at target address.  If target address < current window,
         * assume backward scan, load so that target area is top of window.
         * Note that when switching from forward write to forward read, will have
         * start_row = 0, so the limiting case applies and we load from 0 anyway.
         */
        if (start_row > ptr->cur_start_row) {
          ptr->cur_start_row = start_row;
        } else {
          /* use long arithmetic here to avoid overflow & unsigned problems */
          long ltemp;

          ltemp = (long) end_row - (long) ptr->rows_in_mem;
          if (ltemp < 0)
    	ltemp = 0;		/* don't fall off front end of file */
          ptr->cur_start_row = (JDIMENSION) ltemp;
        }
        /* Read in the selected part of the array.
         * During the initial write pass, we will do no actual read
         * because the selected part is all undefined.
         */
        do_barray_io(cinfo, ptr, FALSE);
      }
      /* Ensure the accessed part of the array is defined; prezero if needed.
       * To improve locality of access, we only prezero the part of the array
       * that the caller is about to access, not the entire in-memory array.
       */
      if (ptr->first_undef_row < end_row) {
        if (ptr->first_undef_row < start_row) {
          if (writable)		/* writer skipped over a section of array */
    	ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);
          undef_row = start_row;	/* but reader is allowed to read ahead */
        } else {
          undef_row = ptr->first_undef_row;
        }
        if (writable)
          ptr->first_undef_row = end_row;
        if (ptr->pre_zero) {
          size_t bytesperrow = (size_t) ptr->blocksperrow * SIZEOF(JBLOCK);
          undef_row -= ptr->cur_start_row; /* make indexes relative to buffer */
          end_row -= ptr->cur_start_row;
          while (undef_row < end_row) {
    	jzero_far((void FAR *) ptr->mem_buffer[undef_row], bytesperrow);
    	undef_row++;
          }
        } else {
          if (! writable)		/* reader looking at undefined data */
    	ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);
        }
      }
      /* Flag the buffer dirty if caller will write in it */
      if (writable)
        ptr->dirty = TRUE;
      /* Return address of proper part of the buffer */
      return ptr->mem_buffer + (start_row - ptr->cur_start_row);
    }

    /*
     * Release all objects belonging to a specified pool.
     */

    METHODDEF(void)
    free_pool (j_common_ptr cinfo, int pool_id)
    {
      my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
      small_pool_ptr shdr_ptr;
      large_pool_ptr lhdr_ptr;
      size_t space_freed;

      if (pool_id < 0 || pool_id >= JPOOL_NUMPOOLS)
        ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */

    #ifdef MEM_STATS
      if (cinfo->err->trace_level > 1)
        print_mem_stats(cinfo, pool_id); /* print pool's memory usage statistics */
    #endif

      /* If freeing IMAGE pool, close any virtual arrays first */
      if (pool_id == JPOOL_IMAGE) {
        jvirt_sarray_ptr sptr;
        jvirt_barray_ptr bptr;

        for (sptr = mem->virt_sarray_list; sptr != NULL; sptr = sptr->next) {
          if (sptr->b_s_open) {	/* there may be no backing store */
    	sptr->b_s_open = FALSE;	/* prevent recursive close if error */
    	(*sptr->b_s_info.close_backing_store) (cinfo, & sptr->b_s_info);
          }
        }
        mem->virt_sarray_list = NULL;
        for (bptr = mem->virt_barray_list; bptr != NULL; bptr = bptr->next) {
          if (bptr->b_s_open) {	/* there may be no backing store */
    	bptr->b_s_open = FALSE;	/* prevent recursive close if error */
    	(*bptr->b_s_info.close_backing_store) (cinfo, & bptr->b_s_info);
          }
        }
        mem->virt_barray_list = NULL;
      }

      /* Release large objects */
      lhdr_ptr = mem->large_list[pool_id];
      mem->large_list[pool_id] = NULL;

      while (lhdr_ptr != NULL) {
        large_pool_ptr next_lhdr_ptr = lhdr_ptr->hdr.next;
        space_freed = lhdr_ptr->hdr.bytes_used +
    		  lhdr_ptr->hdr.bytes_left +
    		  SIZEOF(large_pool_hdr);
        jpeg_free_large(cinfo, (void FAR *) lhdr_ptr, space_freed);
        mem->total_space_allocated -= (long)space_freed;
        lhdr_ptr = next_lhdr_ptr;
      }

      /* Release small objects */
      shdr_ptr = mem->small_list[pool_id];
      mem->small_list[pool_id] = NULL;

      while (shdr_ptr != NULL) {
        small_pool_ptr next_shdr_ptr = shdr_ptr->hdr.next;
        space_freed = shdr_ptr->hdr.bytes_used +
    		  shdr_ptr->hdr.bytes_left +
    		  SIZEOF(small_pool_hdr);
        jpeg_free_small(cinfo, (void *) shdr_ptr, space_freed);
        mem->total_space_allocated -= (long)space_freed;
        shdr_ptr = next_shdr_ptr;
      }
    }

    /*
     * Close up shop entirely.
     * Note that this cannot be called unless cinfo->mem is non-NULL.
     */

    METHODDEF(void)
    self_destruct (j_common_ptr cinfo)
    {
      int pool;

      /* Close all backing store, release all memory.
       * Releasing pools in reverse order might help avoid fragmentation
       * with some (brain-damaged) malloc libraries.
       */
      for (pool = JPOOL_NUMPOOLS-1; pool >= JPOOL_PERMANENT; pool--) {
        free_pool(cinfo, pool);
      }

      /* Release the memory manager control block too. */
      jpeg_free_small(cinfo, (void *) cinfo->mem, SIZEOF(my_memory_mgr));
      cinfo->mem = NULL;		/* ensures I will be called only once */

      jpeg_mem_term(cinfo);		/* system-dependent cleanup */
    }

    /*
     * Memory manager initialization.
     * When this is called, only the error manager pointer is valid in cinfo!
     */

    GLOBAL(void)
    jinit_memory_mgr (j_common_ptr cinfo)
    {
      my_mem_ptr mem;
      long max_to_use;
      int pool;
      size_t test_mac;

      cinfo->mem = NULL;		/* for safety if init fails */

      /* Check for configuration errors.
       * SIZEOF(ALIGN_TYPE) should be a power of 2; otherwise, it probably
       * doesn't reflect any real hardware alignment requirement.
       * The test is a little tricky: for X>0, X and X-1 have no one-bits
       * in common if and only if X is a power of 2, ie has only one one-bit.
       * Some compilers may give an "unreachable code" warning here; ignore it.
       */
      if ((SIZEOF(ALIGN_TYPE) & (SIZEOF(ALIGN_TYPE)-1)) != 0)
        ERREXIT(cinfo, JERR_BAD_ALIGN_TYPE);
      /* MAX_ALLOC_CHUNK must be representable as type size_t, and must be
       * a multiple of SIZEOF(ALIGN_TYPE).
       * Again, an "unreachable code" warning may be ignored here.
       * But a "constant too large" warning means you need to fix MAX_ALLOC_CHUNK.
       */
      test_mac = (size_t) MAX_ALLOC_CHUNK;
      if ((long) test_mac != MAX_ALLOC_CHUNK ||
          (MAX_ALLOC_CHUNK % SIZEOF(ALIGN_TYPE)) != 0)
        ERREXIT(cinfo, JERR_BAD_ALLOC_CHUNK);

      max_to_use = jpeg_mem_init(cinfo); /* system-dependent initialization */

      /* Attempt to allocate memory manager's control block */
      mem = (my_mem_ptr) jpeg_get_small(cinfo, SIZEOF(my_memory_mgr));

      if (mem == NULL) {
        jpeg_mem_term(cinfo);	/* system-dependent cleanup */
        ERREXIT1(cinfo, JERR_OUT_OF_MEMORY, 0);
      }

      /* OK, fill in the method pointers */
      mem->pub.alloc_small = alloc_small;
      mem->pub.alloc_large = alloc_large;
      mem->pub.alloc_sarray = alloc_sarray;
      mem->pub.alloc_barray = alloc_barray;
      mem->pub.request_virt_sarray = request_virt_sarray;
      mem->pub.request_virt_barray = request_virt_barray;
      mem->pub.realize_virt_arrays = realize_virt_arrays;
      mem->pub.access_virt_sarray = access_virt_sarray;
      mem->pub.access_virt_barray = access_virt_barray;
      mem->pub.free_pool = free_pool;
      mem->pub.self_destruct = self_destruct;

      /* Make MAX_ALLOC_CHUNK accessible to other modules */
      mem->pub.max_alloc_chunk = MAX_ALLOC_CHUNK;

      /* Initialize working state */
      mem->pub.max_memory_to_use = max_to_use;

      for (pool = JPOOL_NUMPOOLS-1; pool >= JPOOL_PERMANENT; pool--) {
        mem->small_list[pool] = NULL;
        mem->large_list[pool] = NULL;
      }
      mem->virt_sarray_list = NULL;
      mem->virt_barray_list = NULL;

      mem->total_space_allocated = SIZEOF(my_memory_mgr);

      /* Declare ourselves open for business */
      cinfo->mem = & mem->pub;

      /* Check for an environment variable JPEGMEM; if found, override the
       * default max_memory setting from jpeg_mem_init.  Note that the
       * surrounding application may again override this value.
       * If your system doesn't support getenv(), define NO_GETENV to disable
       * this feature.
       */
    #ifndef NO_GETENV
      { char * memenv;

        if ((memenv = getenv("JPEGMEM")) != NULL) {
          char ch = 'x';

          if (sscanf(memenv, "%ld%c", &max_to_use, &ch) > 0) {
    	if (ch == 'm' || ch == 'M')
    	  max_to_use *= 1000L;
    	mem->pub.max_memory_to_use = max_to_use * 1000L;
          }
        }
      }
    #endif

    }