    /*
     * jquant1.c
     *
     * Copyright (C) 1991-1996, 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 1-pass color quantization (color mapping) routines.
     * These routines provide mapping to a fixed color map using equally spaced
     * color values.  Optional Floyd-Steinberg or ordered dithering is available.
     */

    #define JPEG_INTERNALS
    #include "jinclude.h"
    #include "jpeglib.h"

    #ifdef QUANT_1PASS_SUPPORTED

    /*
     * The main purpose of 1-pass quantization is to provide a fast, if not very
     * high quality, colormapped output capability.  A 2-pass quantizer usually
     * gives better visual quality; however, for quantized grayscale output this
     * quantizer is perfectly adequate.  Dithering is highly recommended with this
     * quantizer, though you can turn it off if you really want to.
     *
     * In 1-pass quantization the colormap must be chosen in advance of seeing the
     * image.  We use a map consisting of all combinations of Ncolors[i] color
     * values for the i'th component.  The Ncolors[] values are chosen so that
     * their product, the total number of colors, is no more than that requested.
     * (In most cases, the product will be somewhat less.)
     *
     * Since the colormap is orthogonal, the representative value for each color
     * component can be determined without considering the other components;
     * then these indexes can be combined into a colormap index by a standard
     * N-dimensional-array-subscript calculation.  Most of the arithmetic involved
     * can be precalculated and stored in the lookup table colorindex[].
     * colorindex[i][j] maps pixel value j in component i to the nearest
     * representative value (grid plane) for that component; this index is
     * multiplied by the array stride for component i, so that the
     * index of the colormap entry closest to a given pixel value is just
     *    sum( colorindex[component-number][pixel-component-value] )
     * Aside from being fast, this scheme allows for variable spacing between
     * representative values with no additional lookup cost.
     *
     * If gamma correction has been applied in color conversion, it might be wise
     * to adjust the color grid spacing so that the representative colors are
     * equidistant in linear space.  At this writing, gamma correction is not
     * implemented by jdcolor, so nothing is done here.
     */

    /* Declarations for ordered dithering.
     *
     * We use a standard 16x16 ordered dither array.  The basic concept of ordered
     * dithering is described in many references, for instance Dale Schumacher's
     * chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991).
     * In place of Schumacher's comparisons against a "threshold" value, we add a
     * "dither" value to the input pixel and then round the result to the nearest
     * output value.  The dither value is equivalent to (0.5 - threshold) times
     * the distance between output values.  For ordered dithering, we assume that
     * the output colors are equally spaced; if not, results will probably be
     * worse, since the dither may be too much or too little at a given point.
     *
     * The normal calculation would be to form pixel value + dither, range-limit
     * this to 0..MAXJSAMPLE, and then index into the colorindex table as usual.
     * We can skip the separate range-limiting step by extending the colorindex
     * table in both directions.
     */

    #define ODITHER_SIZE  16	/* dimension of dither matrix */
    /* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */
    #define ODITHER_CELLS (ODITHER_SIZE*ODITHER_SIZE)	/* # cells in matrix */
    #define ODITHER_MASK  (ODITHER_SIZE-1) /* mask for wrapping around counters */

    typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE];
    typedef int (*ODITHER_MATRIX_PTR)[ODITHER_SIZE];

    static const unsigned char base_dither_matrix[ODITHER_SIZE][ODITHER_SIZE] = {
      /* Bayer's order-4 dither array.  Generated by the code given in
       * Stephen Hawley's article "Ordered Dithering" in Graphics Gems I.
       * The values in this array must range from 0 to ODITHER_CELLS-1.
       */
      {   0,192, 48,240, 12,204, 60,252,  3,195, 51,243, 15,207, 63,255 },
      { 128, 64,176,112,140, 76,188,124,131, 67,179,115,143, 79,191,127 },
      {  32,224, 16,208, 44,236, 28,220, 35,227, 19,211, 47,239, 31,223 },
      { 160, 96,144, 80,172,108,156, 92,163, 99,147, 83,175,111,159, 95 },
      {   8,200, 56,248,  4,196, 52,244, 11,203, 59,251,  7,199, 55,247 },
      { 136, 72,184,120,132, 68,180,116,139, 75,187,123,135, 71,183,119 },
      {  40,232, 24,216, 36,228, 20,212, 43,235, 27,219, 39,231, 23,215 },
      { 168,104,152, 88,164,100,148, 84,171,107,155, 91,167,103,151, 87 },
      {   2,194, 50,242, 14,206, 62,254,  1,193, 49,241, 13,205, 61,253 },
      { 130, 66,178,114,142, 78,190,126,129, 65,177,113,141, 77,189,125 },
      {  34,226, 18,210, 46,238, 30,222, 33,225, 17,209, 45,237, 29,221 },
      { 162, 98,146, 82,174,110,158, 94,161, 97,145, 81,173,109,157, 93 },
      {  10,202, 58,250,  6,198, 54,246,  9,201, 57,249,  5,197, 53,245 },
      { 138, 74,186,122,134, 70,182,118,137, 73,185,121,133, 69,181,117 },
      {  42,234, 26,218, 38,230, 22,214, 41,233, 25,217, 37,229, 21,213 },
      { 170,106,154, 90,166,102,150, 86,169,105,153, 89,165,101,149, 85 }
    };

    /* Declarations for Floyd-Steinberg dithering.
     *
     * Errors are accumulated into the array fserrors[], at a resolution of
     * 1/16th of a pixel count.  The error at a given pixel is propagated
     * to its not-yet-processed neighbors using the standard F-S fractions,
     *		...	(here)	7/16
     *		3/16	5/16	1/16
     * We work left-to-right on even rows, right-to-left on odd rows.
     *
     * We can get away with a single array (holding one row's worth of errors)
     * by using it to store the current row's errors at pixel columns not yet
     * processed, but the next row's errors at columns already processed.  We
     * need only a few extra variables to hold the errors immediately around the
     * current column.  (If we are lucky, those variables are in registers, but
     * even if not, they're probably cheaper to access than array elements are.)
     *
     * The fserrors[] array is indexed [component#][position].
     * We provide (#columns + 2) entries per component; the extra entry at each
     * end saves us from special-casing the first and last pixels.
     *
     * Note: on a wide image, we might not have enough room in a PC's near data
     * segment to hold the error array; so it is allocated with alloc_large.
     */

    #if BITS_IN_JSAMPLE == 8
    typedef short FSERROR;		/* 16 bits should be enough */
    typedef int LOCFSERROR;		/* use 'int' for calculation temps */
    #else
    typedef long FSERROR;		/* may need more than 16 bits */
    typedef long LOCFSERROR;	/* be sure calculation temps are big enough */
    #endif

    typedef FSERROR FAR *FSERRPTR;	/* pointer to error array (in FAR storage!) */

    /* Private subobject */

    #define MAX_Q_COMPS 4		/* max components I can handle */

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

      /* Initially allocated colormap is saved here */
      JSAMPARRAY sv_colormap;	/* The color map as a 2-D pixel array */
      int sv_actual;		/* number of entries in use */

      JSAMPARRAY colorindex;	/* Precomputed mapping for speed */
      /* colorindex[i][j] = index of color closest to pixel value j in component i,
       * premultiplied as described above.  Since colormap indexes must fit into
       * JSAMPLEs, the entries of this array will too.
       */
      int is_padded;		/* is the colorindex padded for odither? */

      int Ncolors[MAX_Q_COMPS];	/* # of values alloced to each component */

      /* Variables for ordered dithering */
      int row_index;		/* cur row's vertical index in dither matrix */
      ODITHER_MATRIX_PTR odither[MAX_Q_COMPS]; /* one dither array per component */

      /* Variables for Floyd-Steinberg dithering */
      FSERRPTR fserrors[MAX_Q_COMPS]; /* accumulated errors */
      int on_odd_row;		/* flag to remember which row we are on */
    } my_cquantizer;

    typedef my_cquantizer * my_cquantize_ptr;

    /*
     * Policy-making subroutines for create_colormap and create_colorindex.
     * These routines determine the colormap to be used.  The rest of the module
     * only assumes that the colormap is orthogonal.
     *
     *  * select_ncolors decides how to divvy up the available colors
     *    among the components.
     *  * output_value defines the set of representative values for a component.
     *  * largest_input_value defines the mapping from input values to
     *    representative values for a component.
     * Note that the latter two routines may impose different policies for
     * different components, though this is not currently done.
     */

    LOCAL(int)
    select_ncolors (j_decompress_ptr cinfo, int Ncolors[])
    /* Determine allocation of desired colors to components, */
    /* and fill in Ncolors[] array to indicate choice. */
    /* Return value is total number of colors (product of Ncolors[] values). */
    {
      int nc = cinfo->out_color_components; /* number of color components */
      int max_colors = cinfo->desired_number_of_colors;
      int total_colors, iroot, i, j;
      int changed;
      long temp;
      static const int RGB_order[3] = { RGB_GREEN, RGB_RED, RGB_BLUE };

      /* We can allocate at least the nc'th root of max_colors per component. */
      /* Compute floor(nc'th root of max_colors). */
      iroot = 1;
      do {
        iroot++;
        temp = iroot;		/* set temp = iroot ** nc */
        for (i = 1; i < nc; i++)
          temp *= iroot;
      } while (temp <= (long) max_colors); /* repeat till iroot exceeds root */
      iroot--;			/* now iroot = floor(root) */

      /* Must have at least 2 color values per component */
      if (iroot < 2)
        ERREXIT1(cinfo, JERR_QUANT_FEW_COLORS, (int) temp);

      /* Initialize to iroot color values for each component */
      total_colors = 1;
      for (i = 0; i < nc; i++) {
        Ncolors[i] = iroot;
        total_colors *= iroot;
      }
      /* We may be able to increment the count for one or more components without
       * exceeding max_colors, though we know not all can be incremented.
       * Sometimes, the first component can be incremented more than once!
       * (Example: for 16 colors, we start at 2*2*2, go to 3*2*2, then 4*2*2.)
       * In RGB colorspace, try to increment G first, then R, then B.
       */
      do {
        changed = FALSE;
        for (i = 0; i < nc; i++) {
          j = (cinfo->out_color_space == JCS_RGB ? RGB_order[i] : i);
          /* calculate new total_colors if Ncolors[j] is incremented */
          temp = total_colors / Ncolors[j];
          temp *= Ncolors[j]+1;	/* done in long arith to avoid oflo */
          if (temp > (long) max_colors)
    	break;			/* won't fit, done with this pass */
          Ncolors[j]++;		/* OK, apply the increment */
          total_colors = (int) temp;
          changed = TRUE;
        }
      } while (changed);

      return total_colors;
    }

    LOCAL(int)
    output_value (j_decompress_ptr , int , int j, int maxj)
    /* Return j'th output value, where j will range from 0 to maxj */
    /* The output values must fall in 0..MAXJSAMPLE in increasing order */
    {
      /* We always provide values 0 and MAXJSAMPLE for each component;
       * any additional values are equally spaced between these limits.
       * (Forcing the upper and lower values to the limits ensures that
       * dithering can't produce a color outside the selected gamut.)
       */
      return (int) (((long) j * MAXJSAMPLE + maxj/2) / maxj);
    }

    LOCAL(int)
    largest_input_value (j_decompress_ptr , int , int j, int maxj)
    /* Return largest input value that should map to j'th output value */
    /* Must have largest(j=0) >= 0, and largest(j=maxj) >= MAXJSAMPLE */
    {
      /* Breakpoints are halfway between values returned by output_value */
      return (int) (((long) (2*j + 1) * MAXJSAMPLE + maxj) / (2*maxj));
    }

    /*
     * Create the colormap.
     */

    LOCAL(void)
    create_colormap (j_decompress_ptr cinfo)
    {
      my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
      JSAMPARRAY colormap;		/* Created colormap */
      int total_colors;		/* Number of distinct output colors */
      int i,j,k, nci, blksize, blkdist, ptr, val;

      /* Select number of colors for each component */
      total_colors = select_ncolors(cinfo, cquantize->Ncolors);

      /* Report selected color counts */
      if (cinfo->out_color_components == 3)
        TRACEMS4(cinfo, 1, JTRC_QUANT_3_NCOLORS,
    	     total_colors, cquantize->Ncolors[0],
    	     cquantize->Ncolors[1], cquantize->Ncolors[2]);
      else
        TRACEMS1(cinfo, 1, JTRC_QUANT_NCOLORS, total_colors);

      /* Allocate and fill in the colormap. */
      /* The colors are ordered in the map in standard row-major order, */
      /* i.e. rightmost (highest-indexed) color changes most rapidly. */

      colormap = (*cinfo->mem->alloc_sarray)
        ((j_common_ptr) cinfo, JPOOL_IMAGE,
         (JDIMENSION) total_colors, (JDIMENSION) cinfo->out_color_components);

      /* blksize is number of adjacent repeated entries for a component */
      /* blkdist is distance between groups of identical entries for a component */
      blkdist = total_colors;

      for (i = 0; i < cinfo->out_color_components; i++) {
        /* fill in colormap entries for i'th color component */
        nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
        blksize = blkdist / nci;
        for (j = 0; j < nci; j++) {
          /* Compute j'th output value (out of nci) for component */
          val = output_value(cinfo, i, j, nci-1);
          /* Fill in all colormap entries that have this value of this component */
          for (ptr = j * blksize; ptr < total_colors; ptr += blkdist) {
    	/* fill in blksize entries beginning at ptr */
    	for (k = 0; k < blksize; k++)
    	  colormap[i][ptr+k] = (JSAMPLE) val;
          }
        }
        blkdist = blksize;		/* blksize of this color is blkdist of next */
      }

      /* Save the colormap in private storage,
       * where it will survive color quantization mode changes.
       */
      cquantize->sv_colormap = colormap;
      cquantize->sv_actual = total_colors;
    }

    /*
     * Create the color index table.
     */

    LOCAL(void)
    create_colorindex (j_decompress_ptr cinfo)
    {
      my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
      JSAMPROW indexptr;
      int i,j,k, nci, blksize, val, pad;

      /* For ordered dither, we pad the color index tables by MAXJSAMPLE in
       * each direction (input index values can be -MAXJSAMPLE .. 2*MAXJSAMPLE).
       * This is not necessary in the other dithering modes.  However, we
       * flag whether it was done in case user changes dithering mode.
       */
      if (cinfo->dither_mode == JDITHER_ORDERED) {
        pad = MAXJSAMPLE*2;
        cquantize->is_padded = TRUE;
      } else {
        pad = 0;
        cquantize->is_padded = FALSE;
      }

      cquantize->colorindex = (*cinfo->mem->alloc_sarray)
        ((j_common_ptr) cinfo, JPOOL_IMAGE,
         (JDIMENSION) (MAXJSAMPLE+1 + pad),
         (JDIMENSION) cinfo->out_color_components);

      /* blksize is number of adjacent repeated entries for a component */
      blksize = cquantize->sv_actual;

      for (i = 0; i < cinfo->out_color_components; i++) {
        /* fill in colorindex entries for i'th color component */
        nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
        blksize = blksize / nci;

        /* adjust colorindex pointers to provide padding at negative indexes. */
        if (pad)
          cquantize->colorindex[i] += MAXJSAMPLE;

        /* in loop, val = index of current output value, */
        /* and k = largest j that maps to current val */
        indexptr = cquantize->colorindex[i];
        val = 0;
        k = largest_input_value(cinfo, i, 0, nci-1);
        for (j = 0; j <= MAXJSAMPLE; j++) {
          while (j > k)		/* advance val if past boundary */
    	k = largest_input_value(cinfo, i, ++val, nci-1);
          /* premultiply so that no multiplication needed in main processing */
          indexptr[j] = (JSAMPLE) (val * blksize);
        }
        /* Pad at both ends if necessary */
        if (pad)
          for (j = 1; j <= MAXJSAMPLE; j++) {
    	indexptr[-j] = indexptr[0];
    	indexptr[MAXJSAMPLE+j] = indexptr[MAXJSAMPLE];
          }
      }
    }

    /*
     * Create an ordered-dither array for a component having ncolors
     * distinct output values.
     */

    LOCAL(ODITHER_MATRIX_PTR)
    make_odither_array (j_decompress_ptr cinfo, int ncolors)
    {
      ODITHER_MATRIX_PTR odither;
      int j,k;
      long num,den;

      odither = (ODITHER_MATRIX_PTR)
        (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
    				SIZEOF(ODITHER_MATRIX));
      /* The inter-value distance for this color is MAXJSAMPLE/(ncolors-1).
       * Hence the dither value for the matrix cell with fill order f
       * (f=0..N-1) should be (N-1-2*f)/(2*N) * MAXJSAMPLE/(ncolors-1).
       * On 16-bit-int machine, be careful to avoid overflow.
       */
      den = 2 * ODITHER_CELLS * ((long) (ncolors - 1));
      for (j = 0; j < ODITHER_SIZE; j++) {
        for (k = 0; k < ODITHER_SIZE; k++) {
          num = ((long) (ODITHER_CELLS-1 - 2*((int)base_dither_matrix[j][k])))
    	    * MAXJSAMPLE;
          /* Ensure round towards zero despite C's lack of consistency
           * about rounding negative values in integer division...
           */
          odither[j][k] = (int) (num<0 ? -((-num)/den) : num/den);
        }
      }
      return odither;
    }

    /*
     * Create the ordered-dither tables.
     * Components having the same number of representative colors may
     * share a dither table.
     */

    LOCAL(void)
    create_odither_tables (j_decompress_ptr cinfo)
    {
      my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
      ODITHER_MATRIX_PTR odither;
      int i, j, nci;

      for (i = 0; i < cinfo->out_color_components; i++) {
        nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
        odither = NULL;		/* search for matching prior component */
        for (j = 0; j < i; j++) {
          if (nci == cquantize->Ncolors[j]) {
    	odither = cquantize->odither[j];
    	break;
          }
        }
        if (odither == NULL)	/* need a new table? */
          odither = make_odither_array(cinfo, nci);
        cquantize->odither[i] = odither;
      }
    }

    /*
     * Map some rows of pixels to the output colormapped representation.
     */

    METHODDEF(void)
    color_quantize (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
    		JSAMPARRAY output_buf, int num_rows)
    /* General case, no dithering */
    {
      my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
      JSAMPARRAY colorindex = cquantize->colorindex;
      register int pixcode, ci;
      register JSAMPROW ptrin, ptrout;
      int row;
      JDIMENSION col;
      JDIMENSION width = cinfo->output_width;
      register int nc = cinfo->out_color_components;

      for (row = 0; row < num_rows; row++) {
        ptrin = input_buf[row];
        ptrout = output_buf[row];
        for (col = width; col > 0; col--) {
          pixcode = 0;
          for (ci = 0; ci < nc; ci++) {
    	pixcode += GETJSAMPLE(colorindex[ci][GETJSAMPLE(*ptrin++)]);
          }
          *ptrout++ = (JSAMPLE) pixcode;
        }
      }
    }

    METHODDEF(void)
    color_quantize3 (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
    		 JSAMPARRAY output_buf, int num_rows)
    /* Fast path for out_color_components==3, no dithering */
    {
      my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
      register int pixcode;
      register JSAMPROW ptrin, ptrout;
      JSAMPROW colorindex0 = cquantize->colorindex[0];
      JSAMPROW colorindex1 = cquantize->colorindex[1];
      JSAMPROW colorindex2 = cquantize->colorindex[2];
      int row;
      JDIMENSION col;
      JDIMENSION width = cinfo->output_width;

      for (row = 0; row < num_rows; row++) {
        ptrin = input_buf[row];
        ptrout = output_buf[row];
        for (col = width; col > 0; col--) {
          pixcode  = GETJSAMPLE(colorindex0[GETJSAMPLE(*ptrin++)]);
          pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*ptrin++)]);
          pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*ptrin++)]);
          *ptrout++ = (JSAMPLE) pixcode;
        }
      }
    }

    METHODDEF(void)
    quantize_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
    		     JSAMPARRAY output_buf, int num_rows)
    /* General case, with ordered dithering */
    {
      my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
      register JSAMPROW input_ptr;
      register JSAMPROW output_ptr;
      JSAMPROW colorindex_ci;
      int * dither;			/* points to active row of dither matrix */
      int row_index, col_index;	/* current indexes into dither matrix */
      int nc = cinfo->out_color_components;
      int ci;
      int row;
      JDIMENSION col;
      JDIMENSION width = cinfo->output_width;

      for (row = 0; row < num_rows; row++) {
        /* Initialize output values to 0 so can process components separately */
        jzero_far((void FAR *) output_buf[row],
    	      (size_t) (width * SIZEOF(JSAMPLE)));
        row_index = cquantize->row_index;
        for (ci = 0; ci < nc; ci++) {
          input_ptr = input_buf[row] + ci;
          output_ptr = output_buf[row];
          colorindex_ci = cquantize->colorindex[ci];
          dither = cquantize->odither[ci][row_index];
          col_index = 0;

          for (col = width; col > 0; col--) {
    	/* Form pixel value + dither, range-limit to 0..MAXJSAMPLE,
    	 * select output value, accumulate into output code for this pixel.
    	 * Range-limiting need not be done explicitly, as we have extended
    	 * the colorindex table to produce the right answers for out-of-range
    	 * inputs.  The maximum dither is +- MAXJSAMPLE; this sets the
    	 * required amount of padding.
    	 */
    	*output_ptr += colorindex_ci[GETJSAMPLE(*input_ptr)+dither[col_index]];
    	input_ptr += nc;
    	output_ptr++;
    	col_index = (col_index + 1) & ODITHER_MASK;
          }
        }
        /* Advance row index for next row */
        row_index = (row_index + 1) & ODITHER_MASK;
        cquantize->row_index = row_index;
      }
    }

    METHODDEF(void)
    quantize3_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
    		      JSAMPARRAY output_buf, int num_rows)
    /* Fast path for out_color_components==3, with ordered dithering */
    {
      my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
      register int pixcode;
      register JSAMPROW input_ptr;
      register JSAMPROW output_ptr;
      JSAMPROW colorindex0 = cquantize->colorindex[0];
      JSAMPROW colorindex1 = cquantize->colorindex[1];
      JSAMPROW colorindex2 = cquantize->colorindex[2];
      int * dither0;		/* points to active row of dither matrix */
      int * dither1;
      int * dither2;
      int row_index, col_index;	/* current indexes into dither matrix */
      int row;
      JDIMENSION col;
      JDIMENSION width = cinfo->output_width;

      for (row = 0; row < num_rows; row++) {
        row_index = cquantize->row_index;
        input_ptr = input_buf[row];
        output_ptr = output_buf[row];
        dither0 = cquantize->odither[0][row_index];
        dither1 = cquantize->odither[1][row_index];
        dither2 = cquantize->odither[2][row_index];
        col_index = 0;

        for (col = width; col > 0; col--) {
          pixcode  = GETJSAMPLE(colorindex0[GETJSAMPLE(*input_ptr++) +
    					dither0[col_index]]);
          pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*input_ptr++) +
    					dither1[col_index]]);
          pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*input_ptr++) +
    					dither2[col_index]]);
          *output_ptr++ = (JSAMPLE) pixcode;
          col_index = (col_index + 1) & ODITHER_MASK;
        }
        row_index = (row_index + 1) & ODITHER_MASK;
        cquantize->row_index = row_index;
      }
    }

    METHODDEF(void)
    quantize_fs_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
    		    JSAMPARRAY output_buf, int num_rows)
    /* General case, with Floyd-Steinberg dithering */
    {
      my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
      register LOCFSERROR cur;	/* current error or pixel value */
      LOCFSERROR belowerr;		/* error for pixel below cur */
      LOCFSERROR bpreverr;		/* error for below/prev col */
      LOCFSERROR bnexterr;		/* error for below/next col */
      LOCFSERROR delta;
      register FSERRPTR errorptr;	/* => fserrors[] at column before current */
      register JSAMPROW input_ptr;
      register JSAMPROW output_ptr;
      JSAMPROW colorindex_ci;
      JSAMPROW colormap_ci;
      int pixcode;
      int nc = cinfo->out_color_components;
      int dir;			/* 1 for left-to-right, -1 for right-to-left */
      int dirnc;			/* dir * nc */
      int ci;
      int row;
      JDIMENSION col;
      JDIMENSION width = cinfo->output_width;
      JSAMPLE *range_limit = cinfo->sample_range_limit;
      SHIFT_TEMPS

      for (row = 0; row < num_rows; row++) {
        /* Initialize output values to 0 so can process components separately */
        jzero_far((void FAR *) output_buf[row],
    	      (size_t) (width * SIZEOF(JSAMPLE)));
        for (ci = 0; ci < nc; ci++) {
          input_ptr = input_buf[row] + ci;
          output_ptr = output_buf[row];
          if (cquantize->on_odd_row) {
    	/* work right to left in this row */
    	input_ptr += (width-1) * nc; /* so point to rightmost pixel */
    	output_ptr += width-1;
    	dir = -1;
    	dirnc = -nc;
    	errorptr = cquantize->fserrors[ci] + (width+1); /* => entry after last column */
          } else {
    	/* work left to right in this row */
    	dir = 1;
    	dirnc = nc;
    	errorptr = cquantize->fserrors[ci]; /* => entry before first column */
          }
          colorindex_ci = cquantize->colorindex[ci];
          colormap_ci = cquantize->sv_colormap[ci];
          /* Preset error values: no error propagated to first pixel from left */
          cur = 0;
          /* and no error propagated to row below yet */
          belowerr = bpreverr = 0;

          for (col = width; col > 0; col--) {
    	/* cur holds the error propagated from the previous pixel on the
    	 * current line.  Add the error propagated from the previous line
    	 * to form the complete error correction term for this pixel, and
    	 * round the error term (which is expressed * 16) to an integer.
    	 * RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct
    	 * for either sign of the error value.
    	 * Note: errorptr points to *previous* column's array entry.
    	 */
    	cur = RIGHT_SHIFT(cur + errorptr[dir] + 8, 4);
    	/* Form pixel value + error, and range-limit to 0..MAXJSAMPLE.
    	 * The maximum error is +- MAXJSAMPLE; this sets the required size
    	 * of the range_limit array.
    	 */
    	cur += GETJSAMPLE(*input_ptr);
    	cur = GETJSAMPLE(range_limit[cur]);
    	/* Select output value, accumulate into output code for this pixel */
    	pixcode = GETJSAMPLE(colorindex_ci[cur]);
    	*output_ptr += (JSAMPLE) pixcode;
    	/* Compute actual representation error at this pixel */
    	/* Note: we can do this even though we don't have the final */
    	/* pixel code, because the colormap is orthogonal. */
    	cur -= GETJSAMPLE(colormap_ci[pixcode]);
    	/* Compute error fractions to be propagated to adjacent pixels.
    	 * Add these into the running sums, and simultaneously shift the
    	 * next-line error sums left by 1 column.
    	 */
    	bnexterr = cur;
    	delta = cur * 2;
    	cur += delta;		/* form error * 3 */
    	errorptr[0] = (FSERROR) (bpreverr + cur);
    	cur += delta;		/* form error * 5 */
    	bpreverr = belowerr + cur;
    	belowerr = bnexterr;
    	cur += delta;		/* form error * 7 */
    	/* At this point cur contains the 7/16 error value to be propagated
    	 * to the next pixel on the current line, and all the errors for the
    	 * next line have been shifted over. We are therefore ready to move on.
    	 */
    	input_ptr += dirnc;	/* advance input ptr to next column */
    	output_ptr += dir;	/* advance output ptr to next column */
    	errorptr += dir;	/* advance errorptr to current column */
          }
          /* Post-loop cleanup: we must unload the final error value into the
           * final fserrors[] entry.  Note we need not unload belowerr because
           * it is for the dummy column before or after the actual array.
           */
          errorptr[0] = (FSERROR) bpreverr; /* unload prev err into array */
        }
        cquantize->on_odd_row = (cquantize->on_odd_row ? FALSE : TRUE);
      }
    }

    /*
     * Allocate workspace for Floyd-Steinberg errors.
     */

    LOCAL(void)
    alloc_fs_workspace (j_decompress_ptr cinfo)
    {
      my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
      size_t arraysize;
      int i;

      arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));
      for (i = 0; i < cinfo->out_color_components; i++) {
        cquantize->fserrors[i] = (FSERRPTR)
          (*cinfo->mem->alloc_large)((j_common_ptr) cinfo, JPOOL_IMAGE, arraysize);
      }
    }

    /*
     * Initialize for one-pass color quantization.
     */

    METHODDEF(void)
    start_pass_1_quant (j_decompress_ptr cinfo, int )
    {
      my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
      size_t arraysize;
      int i;

      /* Install my colormap. */
      cinfo->colormap = cquantize->sv_colormap;
      cinfo->actual_number_of_colors = cquantize->sv_actual;

      /* Initialize for desired dithering mode. */
      switch (cinfo->dither_mode) {
      case JDITHER_NONE:
        if (cinfo->out_color_components == 3)
          cquantize->pub.color_quantize = color_quantize3;
        else
          cquantize->pub.color_quantize = color_quantize;
        break;
      case JDITHER_ORDERED:
        if (cinfo->out_color_components == 3)
          cquantize->pub.color_quantize = quantize3_ord_dither;
        else
          cquantize->pub.color_quantize = quantize_ord_dither;
        cquantize->row_index = 0;	/* initialize state for ordered dither */
        /* If user changed to ordered dither from another mode,
         * we must recreate the color index table with padding.
         * This will cost extra space, but probably isn't very likely.
         */
        if (! cquantize->is_padded)
          create_colorindex(cinfo);
        /* Create ordered-dither tables if we didn't already. */
        if (cquantize->odither[0] == NULL)
          create_odither_tables(cinfo);
        break;
      case JDITHER_FS:
        cquantize->pub.color_quantize = quantize_fs_dither;
        cquantize->on_odd_row = FALSE; /* initialize state for F-S dither */
        /* Allocate Floyd-Steinberg workspace if didn't already. */
        if (cquantize->fserrors[0] == NULL)
          alloc_fs_workspace(cinfo);
        /* Initialize the propagated errors to zero. */
        arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));
        for (i = 0; i < cinfo->out_color_components; i++)
          jzero_far((void FAR *) cquantize->fserrors[i], arraysize);
        break;
      default:
        ERREXIT(cinfo, JERR_NOT_COMPILED);
        break;
      }
    }

    /*
     * Finish up at the end of the pass.
     */

    METHODDEF(void)
    finish_pass_1_quant (j_decompress_ptr )
    {
      /* no work in 1-pass case */
    }

    /*
     * Switch to a new external colormap between output passes.
     * Shouldn't get to this module!
     */

    METHODDEF(void)
    new_color_map_1_quant (j_decompress_ptr cinfo)
    {
      ERREXIT(cinfo, JERR_MODE_CHANGE);
    }

    /*
     * Module initialization routine for 1-pass color quantization.
     */

    GLOBAL(void)
    jinit_1pass_quantizer (j_decompress_ptr cinfo)
    {
      my_cquantize_ptr cquantize;

      cquantize = (my_cquantize_ptr)
        (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
    				SIZEOF(my_cquantizer));
      cinfo->cquantize = (struct jpeg_color_quantizer *) cquantize;
      cquantize->pub.start_pass = start_pass_1_quant;
      cquantize->pub.finish_pass = finish_pass_1_quant;
      cquantize->pub.new_color_map = new_color_map_1_quant;
      cquantize->fserrors[0] = NULL; /* Flag FS workspace not allocated */
      cquantize->odither[0] = NULL;	/* Also flag odither arrays not allocated */

      /* Make sure my internal arrays won't overflow */
      if (cinfo->out_color_components > MAX_Q_COMPS)
        ERREXIT1(cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS);
      /* Make sure colormap indexes can be represented by JSAMPLEs */
      if (cinfo->desired_number_of_colors > (MAXJSAMPLE+1))
        ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE+1);

      /* Create the colormap and color index table. */
      create_colormap(cinfo);
      create_colorindex(cinfo);

      /* Allocate Floyd-Steinberg workspace now if requested.
       * We do this now since it is FAR storage and may affect the memory
       * manager's space calculations.  If the user changes to FS dither
       * mode in a later pass, we will allocate the space then, and will
       * possibly overrun the max_memory_to_use setting.
       */
      if (cinfo->dither_mode == JDITHER_FS)
        alloc_fs_workspace(cinfo);
    }

    #endif /* QUANT_1PASS_SUPPORTED */