code:
/*
 * jquant2.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 2-pass color quantization (color mapping) routines.
 * These routines provide selection of a custom color map for an image,
 * followed by mapping of the image to that color map, with optional
 * Floyd-Steinberg dithering.
 * It is also possible to use just the second pass to map to an arbitrary
 * externally-given color map.
 *
 * Note: ordered dithering is not supported, since there isn't any fast
 * way to compute intercolor distances; it's unclear that ordered dither's
 * fundamental assumptions even hold with an irregularly spaced color map.
 */

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

#ifdef QUANT_2PASS_SUPPORTED

/*
 * This module implements the well-known Heckbert paradigm for color
 * quantization.  Most of the ideas used here can be traced back to
 * Heckbert's seminal paper
 *   Heckbert, Paul.  "Color Image Quantization for Frame Buffer Display",
 *   Proc. SIGGRAPH '82, Computer Graphics v.16 #3 (July 1982), pp 297-304.
 *
 * In the first pass over the image, we accumulate a histogram showing the
 * usage count of each possible color.  To keep the histogram to a reasonable
 * size, we reduce the precision of the input; typical practice is to retain
 * 5 or 6 bits per color, so that 8 or 4 different input values are counted
 * in the same histogram cell.
 *
 * Next, the color-selection step begins with a box representing the whole
 * color space, and repeatedly splits the "largest" remaining box until we
 * have as many boxes as desired colors.  Then the mean color in each
 * remaining box becomes one of the possible output colors.
 *
 * The second pass over the image maps each input pixel to the closest output
 * color (optionally after applying a Floyd-Steinberg dithering correction).
 * This mapping is logically trivial, but making it go fast enough requires
 * considerable care.
 *
 * Heckbert-style quantizers vary a good deal in their policies for choosing
 * the "largest" box and deciding where to cut it.  The particular policies
 * used here have proved out well in experimental comparisons, but better ones
 * may yet be found.
 *
 * In earlier versions of the IJG code, this module quantized in YCbCr color
 * space, processing the raw upsampled data without a color conversion step.
 * This allowed the color conversion math to be done only once per colormap
 * entry, not once per pixel.  However, that optimization precluded other
 * useful optimizations (such as merging color conversion with upsampling)
 * and it also interfered with desired capabilities such as quantizing to an
 * externally-supplied colormap.  We have therefore abandoned that approach.
 * The present code works in the post-conversion color space, typically RGB.
 *
 * To improve the visual quality of the results, we actually work in scaled
 * RGB space, giving G distances more weight than R, and R in turn more than
 * B.  To do everything in integer math, we must use integer scale factors.
 * The 2/3/1 scale factors used here correspond loosely to the relative
 * weights of the colors in the NTSC grayscale equation.
 * If you want to use this code to quantize a non-RGB color space, you'll
 * probably need to change these scale factors.
 */

#define R_SCALE 2		/* scale R distances by this much */
#define G_SCALE 3		/* scale G distances by this much */
#define B_SCALE 1		/* and B by this much */

/* Relabel R/G/B as components 0/1/2, respecting the RGB ordering defined
 * in jmorecfg.h.  As the code stands, it will do the right thing for R,G,B
 * and B,G,R orders.  If you define some other weird order in jmorecfg.h,
 * you'll get compile errors until you extend this logic.  In that case
 * you'll probably want to tweak the histogram sizes too.
 */

#if RGB_RED == 0
#define C0_SCALE R_SCALE
#endif
#if RGB_BLUE == 0
#define C0_SCALE B_SCALE
#endif
#if RGB_GREEN == 1
#define C1_SCALE G_SCALE
#endif
#if RGB_RED == 2
#define C2_SCALE R_SCALE
#endif
#if RGB_BLUE == 2
#define C2_SCALE B_SCALE
#endif

/*
 * First we have the histogram data structure and routines for creating it.
 *
 * The number of bits of precision can be adjusted by changing these symbols.
 * We recommend keeping 6 bits for G and 5 each for R and B.
 * If you have plenty of memory and cycles, 6 bits all around gives marginally
 * better results; if you are short of memory, 5 bits all around will save
 * some space but degrade the results.
 * To maintain a fully accurate histogram, we'd need to allocate a "long"
 * (preferably unsigned long) for each cell.  In practice this is overkill;
 * we can get by with 16 bits per cell.  Few of the cell counts will overflow,
 * and clamping those that do overflow to the maximum value will give close-
 * enough results.  This reduces the recommended histogram size from 256Kb
 * to 128Kb, which is a useful savings on PC-class machines.
 * (In the second pass the histogram space is re-used for pixel mapping data;
 * in that capacity, each cell must be able to store zero to the number of
 * desired colors.  16 bits/cell is plenty for that too.)
 * Since the JPEG code is intended to run in small memory model on 80x86
 * machines, we can't just allocate the histogram in one chunk.  Instead
 * of a true 3-D array, we use a row of pointers to 2-D arrays.  Each
 * pointer corresponds to a C0 value (typically 2^5 = 32 pointers) and
 * each 2-D array has 2^6*2^5 = 2048 or 2^6*2^6 = 4096 entries.  Note that
 * on 80x86 machines, the pointer row is in near memory but the actual
 * arrays are in far memory (same arrangement as we use for image arrays).
 */

#define MAXNUMCOLORS  (MAXJSAMPLE+1) /* maximum size of colormap */

/* These will do the right thing for either R,G,B or B,G,R color order,
 * but you may not like the results for other color orders.
 */
#define HIST_C0_BITS  5		/* bits of precision in R/B histogram */
#define HIST_C1_BITS  6		/* bits of precision in G histogram */
#define HIST_C2_BITS  5		/* bits of precision in B/R histogram */

/* Number of elements along histogram axes. */
#define HIST_C0_ELEMS  (1<<HIST_C0_BITS)
#define HIST_C1_ELEMS  (1<<HIST_C1_BITS)
#define HIST_C2_ELEMS  (1<<HIST_C2_BITS)

/* These are the amounts to shift an input value to get a histogram index. */
#define C0_SHIFT  (BITS_IN_JSAMPLE-HIST_C0_BITS)
#define C1_SHIFT  (BITS_IN_JSAMPLE-HIST_C1_BITS)
#define C2_SHIFT  (BITS_IN_JSAMPLE-HIST_C2_BITS)

typedef UINT16 histcell;	/* histogram cell; prefer an unsigned type */

typedef histcell FAR * histptr;	/* for pointers to histogram cells */

typedef histcell hist1d[HIST_C2_ELEMS]; /* typedefs for the array */
typedef hist1d FAR * hist2d;	/* type for the 2nd-level pointers */
typedef hist2d * hist3d;	/* type for top-level pointer */

/* 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 has (#columns + 2) entries; the extra entry at
 * each end saves us from special-casing the first and last pixels.
 * Each entry is three values long, one value for each color component.
 *
 * 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 INT16 FSERROR;		/* 16 bits should be enough */
typedef int LOCFSERROR;		/* use 'int' for calculation temps */
#else
typedef INT32 FSERROR;		/* may need more than 16 bits */
typedef INT32 LOCFSERROR;	/* be sure calculation temps are big enough */
#endif

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

/* Private subobject */

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

  /* Space for the eventually created colormap is stashed here */
  JSAMPARRAY sv_colormap;	/* colormap allocated at init time */
  int desired;			/* desired # of colors = size of colormap */

  /* Variables for accumulating image statistics */
  hist3d histogram;		/* pointer to the histogram */

  boolean needs_zeroed;		/* TRUE if next pass must zero histogram */

  /* Variables for Floyd-Steinberg dithering */
  FSERRPTR fserrors;		/* accumulated errors */
  boolean on_odd_row;		/* flag to remember which row we are on */
  int * error_limiter;		/* table for clamping the applied error */
} my_cquantizer;

typedef my_cquantizer * my_cquantize_ptr;

/*
 * Prescan some rows of pixels.
 * In this module the prescan simply updates the histogram, which has been
 * initialized to zeroes by start_pass.
 * An output_buf parameter is required by the method signature, but no data
 * is actually output (in fact the buffer controller is probably passing a
 * NULL pointer).
 */

METHODDEF(void)
prescan_quantize (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
		  JSAMPARRAY output_buf, int num_rows)
{
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
  register JSAMPROW ptr;
  register histptr histp;
  register hist3d histogram = cquantize->histogram;
  int row;
  JDIMENSION col;
  JDIMENSION width = cinfo->output_width;

  for (row = 0; row < num_rows; row++) {
    ptr = input_buf[row];
    for (col = width; col > 0; col--) {
      /* get pixel value and index into the histogram */
      histp = & histogram[GETJSAMPLE(ptr[0]) >> C0_SHIFT]
			 [GETJSAMPLE(ptr[1]) >> C1_SHIFT]
			 [GETJSAMPLE(ptr[2]) >> C2_SHIFT];
      /* increment, check for overflow and undo increment if so. */
      if (++(*histp) <= 0)
	(*histp)--;
      ptr += 3;
    }
  }
}

/*
 * Next we have the really interesting routines: selection of a colormap
 * given the completed histogram.
 * These routines work with a list of "boxes", each representing a rectangular
 * subset of the input color space (to histogram precision).
 */

typedef struct {
  /* The bounds of the box (inclusive); expressed as histogram indexes */
  int c0min, c0max;
  int c1min, c1max;
  int c2min, c2max;
  /* The volume (actually 2-norm) of the box */
  INT32 volume;
  /* The number of nonzero histogram cells within this box */
  long colorcount;
} box;

typedef box * boxptr;

LOCAL(boxptr)
find_biggest_color_pop (boxptr boxlist, int numboxes)
/* Find the splittable box with the largest color population */
/* Returns NULL if no splittable boxes remain */
{
  register boxptr boxp;
  register int i;
  register long maxc = 0;
  boxptr which = NULL;

  for (i = 0, boxp = boxlist; i < numboxes; i++, boxp++) {
    if (boxp->colorcount > maxc && boxp->volume > 0) {
      which = boxp;
      maxc = boxp->colorcount;
    }
  }
  return which;
}

LOCAL(boxptr)
find_biggest_volume (boxptr boxlist, int numboxes)
/* Find the splittable box with the largest (scaled) volume */
/* Returns NULL if no splittable boxes remain */
{
  register boxptr boxp;
  register int i;
  register INT32 maxv = 0;
  boxptr which = NULL;

  for (i = 0, boxp = boxlist; i < numboxes; i++, boxp++) {
    if (boxp->volume > maxv) {
      which = boxp;
      maxv = boxp->volume;
    }
  }
  return which;
}

LOCAL(void)
update_box (j_decompress_ptr cinfo, boxptr boxp)
/* Shrink the min/max bounds of a box to enclose only nonzero elements, */
/* and recompute its volume and population */
{
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  histptr histp;
  int c0,c1,c2;
  int c0min,c0max,c1min,c1max,c2min,c2max;
  INT32 dist0,dist1,dist2;
  long ccount;

  c0min = boxp->c0min;  c0max = boxp->c0max;
  c1min = boxp->c1min;  c1max = boxp->c1max;
  c2min = boxp->c2min;  c2max = boxp->c2max;

  if (c0max > c0min)
    for (c0 = c0min; c0 <= c0max; c0++)
      for (c1 = c1min; c1 <= c1max; c1++) {
	histp = & histogram[c0][c1][c2min];
	for (c2 = c2min; c2 <= c2max; c2++)
	  if (*histp++ != 0) {
	    boxp->c0min = c0min = c0;
	    goto have_c0min;
	  }
      }
 have_c0min:
  if (c0max > c0min)
    for (c0 = c0max; c0 >= c0min; c0--)
      for (c1 = c1min; c1 <= c1max; c1++) {
	histp = & histogram[c0][c1][c2min];
	for (c2 = c2min; c2 <= c2max; c2++)
	  if (*histp++ != 0) {
	    boxp->c0max = c0max = c0;
	    goto have_c0max;
	  }
      }
 have_c0max:
  if (c1max > c1min)
    for (c1 = c1min; c1 <= c1max; c1++)
      for (c0 = c0min; c0 <= c0max; c0++) {
	histp = & histogram[c0][c1][c2min];
	for (c2 = c2min; c2 <= c2max; c2++)
	  if (*histp++ != 0) {
	    boxp->c1min = c1min = c1;
	    goto have_c1min;
	  }
      }
 have_c1min:
  if (c1max > c1min)
    for (c1 = c1max; c1 >= c1min; c1--)
      for (c0 = c0min; c0 <= c0max; c0++) {
	histp = & histogram[c0][c1][c2min];
	for (c2 = c2min; c2 <= c2max; c2++)
	  if (*histp++ != 0) {
	    boxp->c1max = c1max = c1;
	    goto have_c1max;
	  }
      }
 have_c1max:
  if (c2max > c2min)
    for (c2 = c2min; c2 <= c2max; c2++)
      for (c0 = c0min; c0 <= c0max; c0++) {
	histp = & histogram[c0][c1min][c2];
	for (c1 = c1min; c1 <= c1max; c1++, histp += HIST_C2_ELEMS)
	  if (*histp != 0) {
	    boxp->c2min = c2min = c2;
	    goto have_c2min;
	  }
      }
 have_c2min:
  if (c2max > c2min)
    for (c2 = c2max; c2 >= c2min; c2--)
      for (c0 = c0min; c0 <= c0max; c0++) {
	histp = & histogram[c0][c1min][c2];
	for (c1 = c1min; c1 <= c1max; c1++, histp += HIST_C2_ELEMS)
	  if (*histp != 0) {
	    boxp->c2max = c2max = c2;
	    goto have_c2max;
	  }
      }
 have_c2max:

  /* Update box volume.
   * We use 2-norm rather than real volume here; this biases the method
   * against making long narrow boxes, and it has the side benefit that
   * a box is splittable iff norm > 0.
   * Since the differences are expressed in histogram-cell units,
   * we have to shift back to JSAMPLE units to get consistent distances;
   * after which, we scale according to the selected distance scale factors.
   */
  dist0 = ((c0max - c0min) << C0_SHIFT) * C0_SCALE;
  dist1 = ((c1max - c1min) << C1_SHIFT) * C1_SCALE;
  dist2 = ((c2max - c2min) << C2_SHIFT) * C2_SCALE;
  boxp->volume = dist0*dist0 + dist1*dist1 + dist2*dist2;

  /* Now scan remaining volume of box and compute population */
  ccount = 0;
  for (c0 = c0min; c0 <= c0max; c0++)
    for (c1 = c1min; c1 <= c1max; c1++) {
      histp = & histogram[c0][c1][c2min];
      for (c2 = c2min; c2 <= c2max; c2++, histp++)
	if (*histp != 0) {
	  ccount++;
	}
    }
  boxp->colorcount = ccount;
}

LOCAL(int)
median_cut (j_decompress_ptr cinfo, boxptr boxlist, int numboxes,
	    int desired_colors)
/* Repeatedly select and split the largest box until we have enough boxes */
{
  int n,lb;
  int c0,c1,c2,cmax;
  register boxptr b1,b2;

  while (numboxes < desired_colors) {
    /* Select box to split.
     * Current algorithm: by population for first half, then by volume.
     */
    if (numboxes*2 <= desired_colors) {
      b1 = find_biggest_color_pop(boxlist, numboxes);
    } else {
      b1 = find_biggest_volume(boxlist, numboxes);
    }
    if (b1 == NULL)		/* no splittable boxes left! */
      break;
    b2 = &boxlist[numboxes];	/* where new box will go */
    /* Copy the color bounds to the new box. */
    b2->c0max = b1->c0max; b2->c1max = b1->c1max; b2->c2max = b1->c2max;
    b2->c0min = b1->c0min; b2->c1min = b1->c1min; b2->c2min = b1->c2min;
    /* Choose which axis to split the box on.
     * Current algorithm: longest scaled axis.
     * See notes in update_box about scaling distances.
     */
    c0 = ((b1->c0max - b1->c0min) << C0_SHIFT) * C0_SCALE;
    c1 = ((b1->c1max - b1->c1min) << C1_SHIFT) * C1_SCALE;
    c2 = ((b1->c2max - b1->c2min) << C2_SHIFT) * C2_SCALE;
    /* We want to break any ties in favor of green, then red, blue last.
     * This code does the right thing for R,G,B or B,G,R color orders only.
     */
#if RGB_RED == 0
    cmax = c1; n = 1;
    if (c0 > cmax) { cmax = c0; n = 0; }
    if (c2 > cmax) { n = 2; }
#else
    cmax = c1; n = 1;
    if (c2 > cmax) { cmax = c2; n = 2; }
    if (c0 > cmax) { n = 0; }
#endif
    /* Choose split point along selected axis, and update box bounds.
     * Current algorithm: split at halfway point.
     * (Since the box has been shrunk to minimum volume,
     * any split will produce two nonempty subboxes.)
     * Note that lb value is max for lower box, so must be < old max.
     */
    switch (n) {
    case 0:
      lb = (b1->c0max + b1->c0min) / 2;
      b1->c0max = lb;
      b2->c0min = lb+1;
      break;
    case 1:
      lb = (b1->c1max + b1->c1min) / 2;
      b1->c1max = lb;
      b2->c1min = lb+1;
      break;
    case 2:
      lb = (b1->c2max + b1->c2min) / 2;
      b1->c2max = lb;
      b2->c2min = lb+1;
      break;
    }
    /* Update stats for boxes */
    update_box(cinfo, b1);
    update_box(cinfo, b2);
    numboxes++;
  }
  return numboxes;
}

LOCAL(void)
compute_color (j_decompress_ptr cinfo, boxptr boxp, int icolor)
/* Compute representative color for a box, put it in colormap[icolor] */
{
  /* Current algorithm: mean weighted by pixels (not colors) */
  /* Note it is important to get the rounding correct! */
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  histptr histp;
  int c0,c1,c2;
  int c0min,c0max,c1min,c1max,c2min,c2max;
  long count;
  long total = 0;
  long c0total = 0;
  long c1total = 0;
  long c2total = 0;

  c0min = boxp->c0min;  c0max = boxp->c0max;
  c1min = boxp->c1min;  c1max = boxp->c1max;
  c2min = boxp->c2min;  c2max = boxp->c2max;

  for (c0 = c0min; c0 <= c0max; c0++)
    for (c1 = c1min; c1 <= c1max; c1++) {
      histp = & histogram[c0][c1][c2min];
      for (c2 = c2min; c2 <= c2max; c2++) {
	if ((count = *histp++) != 0) {
	  total += count;
	  c0total += ((c0 << C0_SHIFT) + ((1<<C0_SHIFT)>>1)) * count;
	  c1total += ((c1 << C1_SHIFT) + ((1<<C1_SHIFT)>>1)) * count;
	  c2total += ((c2 << C2_SHIFT) + ((1<<C2_SHIFT)>>1)) * count;
	}
      }
    }

  cinfo->colormap[0][icolor] = (JSAMPLE) ((c0total + (total>>1)) / total);
  cinfo->colormap[1][icolor] = (JSAMPLE) ((c1total + (total>>1)) / total);
  cinfo->colormap[2][icolor] = (JSAMPLE) ((c2total + (total>>1)) / total);
}

LOCAL(void)
select_colors (j_decompress_ptr cinfo, int desired_colors)
/* Master routine for color selection */
{
  boxptr boxlist;
  int numboxes;
  int i;

  /* Allocate workspace for box list */
  boxlist = (boxptr) (*cinfo->mem->alloc_small)
    ((j_common_ptr) cinfo, JPOOL_IMAGE, desired_colors * SIZEOF(box));
  /* Initialize one box containing whole space */
  numboxes = 1;
  boxlist[0].c0min = 0;
  boxlist[0].c0max = MAXJSAMPLE >> C0_SHIFT;
  boxlist[0].c1min = 0;
  boxlist[0].c1max = MAXJSAMPLE >> C1_SHIFT;
  boxlist[0].c2min = 0;
  boxlist[0].c2max = MAXJSAMPLE >> C2_SHIFT;
  /* Shrink it to actually-used volume and set its statistics */
  update_box(cinfo, & boxlist[0]);
  /* Perform median-cut to produce final box list */
  numboxes = median_cut(cinfo, boxlist, numboxes, desired_colors);
  /* Compute the representative color for each box, fill colormap */
  for (i = 0; i < numboxes; i++)
    compute_color(cinfo, & boxlist[i], i);
  cinfo->actual_number_of_colors = numboxes;
  TRACEMS1(cinfo, 1, JTRC_QUANT_SELECTED, numboxes);
}

/*
 * These routines are concerned with the time-critical task of mapping input
 * colors to the nearest color in the selected colormap.
 *
 * We re-use the histogram space as an "inverse color map", essentially a
 * cache for the results of nearest-color searches.  All colors within a
 * histogram cell will be mapped to the same colormap entry, namely the one
 * closest to the cell's center.  This may not be quite the closest entry to
 * the actual input color, but it's almost as good.  A zero in the cache
 * indicates we haven't found the nearest color for that cell yet; the array
 * is cleared to zeroes before starting the mapping pass.  When we find the
 * nearest color for a cell, its colormap index plus one is recorded in the
 * cache for future use.  The pass2 scanning routines call fill_inverse_cmap
 * when they need to use an unfilled entry in the cache.
 *
 * Our method of efficiently finding nearest colors is based on the "locally
 * sorted search" idea described by Heckbert and on the incremental distance
 * calculation described by Spencer W. Thomas in chapter III.1 of Graphics
 * Gems II (James Arvo, ed.  Academic Press, 1991).  Thomas points out that
 * the distances from a given colormap entry to each cell of the histogram can
 * be computed quickly using an incremental method: the differences between
 * distances to adjacent cells themselves differ by a constant.  This allows a
 * fairly fast implementation of the "brute force" approach of computing the
 * distance from every colormap entry to every histogram cell.  Unfortunately,
 * it needs a work array to hold the best-distance-so-far for each histogram
 * cell (because the inner loop has to be over cells, not colormap entries).
 * The work array elements have to be INT32s, so the work array would need
 * 256Kb at our recommended precision.  This is not feasible in DOS machines.
 *
 * To get around these problems, we apply Thomas' method to compute the
 * nearest colors for only the cells within a small subbox of the histogram.
 * The work array need be only as big as the subbox, so the memory usage
 * problem is solved.  Furthermore, we need not fill subboxes that are never
 * referenced in pass2; many images use only part of the color gamut, so a
 * fair amount of work is saved.  An additional advantage of this
 * approach is that we can apply Heckbert's locality criterion to quickly
 * eliminate colormap entries that are far away from the subbox; typically
 * three-fourths of the colormap entries are rejected by Heckbert's criterion,
 * and we need not compute their distances to individual cells in the subbox.
 * The speed of this approach is heavily influenced by the subbox size: too
 * small means too much overhead, too big loses because Heckbert's criterion
 * can't eliminate as many colormap entries.  Empirically the best subbox
 * size seems to be about 1/512th of the histogram (1/8th in each direction).
 *
 * Thomas' article also describes a refined method which is asymptotically
 * faster than the brute-force method, but it is also far more complex and
 * cannot efficiently be applied to small subboxes.  It is therefore not
 * useful for programs intended to be portable to DOS machines.  On machines
 * with plenty of memory, filling the whole histogram in one shot with Thomas'
 * refined method might be faster than the present code --- but then again,
 * it might not be any faster, and it's certainly more complicated.
 */

/* log2(histogram cells in update box) for each axis; this can be adjusted */
#define BOX_C0_LOG  (HIST_C0_BITS-3)
#define BOX_C1_LOG  (HIST_C1_BITS-3)
#define BOX_C2_LOG  (HIST_C2_BITS-3)

#define BOX_C0_ELEMS  (1<<BOX_C0_LOG) /* # of hist cells in update box */
#define BOX_C1_ELEMS  (1<<BOX_C1_LOG)
#define BOX_C2_ELEMS  (1<<BOX_C2_LOG)

#define BOX_C0_SHIFT  (C0_SHIFT + BOX_C0_LOG)
#define BOX_C1_SHIFT  (C1_SHIFT + BOX_C1_LOG)
#define BOX_C2_SHIFT  (C2_SHIFT + BOX_C2_LOG)

/*
 * The next three routines implement inverse colormap filling.  They could
 * all be folded into one big routine, but splitting them up this way saves
 * some stack space (the mindist[] and bestdist[] arrays need not coexist)
 * and may allow some compilers to produce better code by registerizing more
 * inner-loop variables.
 */

LOCAL(int)
find_nearby_colors (j_decompress_ptr cinfo, int minc0, int minc1, int minc2,
		    JSAMPLE colorlist[])
/* Locate the colormap entries close enough to an update box to be candidates
 * for the nearest entry to some cell(s) in the update box.  The update box
 * is specified by the center coordinates of its first cell.  The number of
 * candidate colormap entries is returned, and their colormap indexes are
 * placed in colorlist[].
 * This routine uses Heckbert's "locally sorted search" criterion to select
 * the colors that need further consideration.
 */
{
  int numcolors = cinfo->actual_number_of_colors;
  int maxc0, maxc1, maxc2;
  int centerc0, centerc1, centerc2;
  int i, x, ncolors;
  INT32 minmaxdist, min_dist, max_dist, tdist;
  INT32 mindist[MAXNUMCOLORS];	/* min distance to colormap entry i */

  /* Compute true coordinates of update box's upper corner and center.
   * Actually we compute the coordinates of the center of the upper-corner
   * histogram cell, which are the upper bounds of the volume we care about.
   * Note that since ">>" rounds down, the "center" values may be closer to
   * min than to max; hence comparisons to them must be "<=", not "<".
   */
  maxc0 = minc0 + ((1 << BOX_C0_SHIFT) - (1 << C0_SHIFT));
  centerc0 = (minc0 + maxc0) >> 1;
  maxc1 = minc1 + ((1 << BOX_C1_SHIFT) - (1 << C1_SHIFT));
  centerc1 = (minc1 + maxc1) >> 1;
  maxc2 = minc2 + ((1 << BOX_C2_SHIFT) - (1 << C2_SHIFT));
  centerc2 = (minc2 + maxc2) >> 1;

  /* For each color in colormap, find:
   *  1. its minimum squared-distance to any point in the update box
   *     (zero if color is within update box);
   *  2. its maximum squared-distance to any point in the update box.
   * Both of these can be found by considering only the corners of the box.
   * We save the minimum distance for each color in mindist[];
   * only the smallest maximum distance is of interest.
   */
  minmaxdist = 0x7FFFFFFFL;

  for (i = 0; i < numcolors; i++) {
    /* We compute the squared-c0-distance term, then add in the other two. */
    x = GETJSAMPLE(cinfo->colormap[0][i]);
    if (x < minc0) {
      tdist = (x - minc0) * C0_SCALE;
      min_dist = tdist*tdist;
      tdist = (x - maxc0) * C0_SCALE;
      max_dist = tdist*tdist;
    } else if (x > maxc0) {
      tdist = (x - maxc0) * C0_SCALE;
      min_dist = tdist*tdist;
      tdist = (x - minc0) * C0_SCALE;
      max_dist = tdist*tdist;
    } else {
      /* within cell range so no contribution to min_dist */
      min_dist = 0;
      if (x <= centerc0) {
	tdist = (x - maxc0) * C0_SCALE;
	max_dist = tdist*tdist;
      } else {
	tdist = (x - minc0) * C0_SCALE;
	max_dist = tdist*tdist;
      }
    }

    x = GETJSAMPLE(cinfo->colormap[1][i]);
    if (x < minc1) {
      tdist = (x - minc1) * C1_SCALE;
      min_dist += tdist*tdist;
      tdist = (x - maxc1) * C1_SCALE;
      max_dist += tdist*tdist;
    } else if (x > maxc1) {
      tdist = (x - maxc1) * C1_SCALE;
      min_dist += tdist*tdist;
      tdist = (x - minc1) * C1_SCALE;
      max_dist += tdist*tdist;
    } else {
      /* within cell range so no contribution to min_dist */
      if (x <= centerc1) {
	tdist = (x - maxc1) * C1_SCALE;
	max_dist += tdist*tdist;
      } else {
	tdist = (x - minc1) * C1_SCALE;
	max_dist += tdist*tdist;
      }
    }

    x = GETJSAMPLE(cinfo->colormap[2][i]);
    if (x < minc2) {
      tdist = (x - minc2) * C2_SCALE;
      min_dist += tdist*tdist;
      tdist = (x - maxc2) * C2_SCALE;
      max_dist += tdist*tdist;
    } else if (x > maxc2) {
      tdist = (x - maxc2) * C2_SCALE;
      min_dist += tdist*tdist;
      tdist = (x - minc2) * C2_SCALE;
      max_dist += tdist*tdist;
    } else {
      /* within cell range so no contribution to min_dist */
      if (x <= centerc2) {
	tdist = (x - maxc2) * C2_SCALE;
	max_dist += tdist*tdist;
      } else {
	tdist = (x - minc2) * C2_SCALE;
	max_dist += tdist*tdist;
      }
    }

    mindist[i] = min_dist;	/* save away the results */
    if (max_dist < minmaxdist)
      minmaxdist = max_dist;
  }

  /* Now we know that no cell in the update box is more than minmaxdist
   * away from some colormap entry.  Therefore, only colors that are
   * within minmaxdist of some part of the box need be considered.
   */
  ncolors = 0;
  for (i = 0; i < numcolors; i++) {
    if (mindist[i] <= minmaxdist)
      colorlist[ncolors++] = (JSAMPLE) i;
  }
  return ncolors;
}

LOCAL(void)
find_best_colors (j_decompress_ptr cinfo, int minc0, int minc1, int minc2,
		  int numcolors, JSAMPLE colorlist[], JSAMPLE bestcolor[])
/* Find the closest colormap entry for each cell in the update box,
 * given the list of candidate colors prepared by find_nearby_colors.
 * Return the indexes of the closest entries in the bestcolor[] array.
 * This routine uses Thomas' incremental distance calculation method to
 * find the distance from a colormap entry to successive cells in the box.
 */
{
  int ic0, ic1, ic2;
  int i, icolor;
  register INT32 * bptr;	/* pointer into bestdist[] array */
  JSAMPLE * cptr;		/* pointer into bestcolor[] array */
  INT32 dist0, dist1;		/* initial distance values */
  register INT32 dist2;		/* current distance in inner loop */
  INT32 xx0, xx1;		/* distance increments */
  register INT32 xx2;
  INT32 inc0, inc1, inc2;	/* initial values for increments */
  /* This array holds the distance to the nearest-so-far color for each cell */
  INT32 bestdist[BOX_C0_ELEMS * BOX_C1_ELEMS * BOX_C2_ELEMS];

  /* Initialize best-distance for each cell of the update box */
  bptr = bestdist;
  for (i = BOX_C0_ELEMS*BOX_C1_ELEMS*BOX_C2_ELEMS-1; i >= 0; i--)
    *bptr++ = 0x7FFFFFFFL;

  /* For each color selected by find_nearby_colors,
   * compute its distance to the center of each cell in the box.
   * If that's less than best-so-far, update best distance and color number.
   */

  /* Nominal steps between cell centers ("x" in Thomas article) */
#define STEP_C0  ((1 << C0_SHIFT) * C0_SCALE)
#define STEP_C1  ((1 << C1_SHIFT) * C1_SCALE)
#define STEP_C2  ((1 << C2_SHIFT) * C2_SCALE)

  for (i = 0; i < numcolors; i++) {
    icolor = GETJSAMPLE(colorlist[i]);
    /* Compute (square of) distance from minc0/c1/c2 to this color */
    inc0 = (minc0 - GETJSAMPLE(cinfo->colormap[0][icolor])) * C0_SCALE;
    dist0 = inc0*inc0;
    inc1 = (minc1 - GETJSAMPLE(cinfo->colormap[1][icolor])) * C1_SCALE;
    dist0 += inc1*inc1;
    inc2 = (minc2 - GETJSAMPLE(cinfo->colormap[2][icolor])) * C2_SCALE;
    dist0 += inc2*inc2;
    /* Form the initial difference increments */
    inc0 = inc0 * (2 * STEP_C0) + STEP_C0 * STEP_C0;
    inc1 = inc1 * (2 * STEP_C1) + STEP_C1 * STEP_C1;
    inc2 = inc2 * (2 * STEP_C2) + STEP_C2 * STEP_C2;
    /* Now loop over all cells in box, updating distance per Thomas method */
    bptr = bestdist;
    cptr = bestcolor;
    xx0 = inc0;
    for (ic0 = BOX_C0_ELEMS-1; ic0 >= 0; ic0--) {
      dist1 = dist0;
      xx1 = inc1;
      for (ic1 = BOX_C1_ELEMS-1; ic1 >= 0; ic1--) {
	dist2 = dist1;
	xx2 = inc2;
	for (ic2 = BOX_C2_ELEMS-1; ic2 >= 0; ic2--) {
	  if (dist2 < *bptr) {
	    *bptr = dist2;
	    *cptr = (JSAMPLE) icolor;
	  }
	  dist2 += xx2;
	  xx2 += 2 * STEP_C2 * STEP_C2;
	  bptr++;
	  cptr++;
	}
	dist1 += xx1;
	xx1 += 2 * STEP_C1 * STEP_C1;
      }
      dist0 += xx0;
      xx0 += 2 * STEP_C0 * STEP_C0;
    }
  }
}

LOCAL(void)
fill_inverse_cmap (j_decompress_ptr cinfo, int c0, int c1, int c2)
/* Fill the inverse-colormap entries in the update box that contains */
/* histogram cell c0/c1/c2.  (Only that one cell MUST be filled, but */
/* we can fill as many others as we wish.) */
{
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  int minc0, minc1, minc2;	/* lower left corner of update box */
  int ic0, ic1, ic2;
  register JSAMPLE * cptr;	/* pointer into bestcolor[] array */
  register histptr cachep;	/* pointer into main cache array */
  /* This array lists the candidate colormap indexes. */
  JSAMPLE colorlist[MAXNUMCOLORS];
  int numcolors;		/* number of candidate colors */
  /* This array holds the actually closest colormap index for each cell. */
  JSAMPLE bestcolor[BOX_C0_ELEMS * BOX_C1_ELEMS * BOX_C2_ELEMS];

  /* Convert cell coordinates to update box ID */
  c0 >>= BOX_C0_LOG;
  c1 >>= BOX_C1_LOG;
  c2 >>= BOX_C2_LOG;

  /* Compute true coordinates of update box's origin corner.
   * Actually we compute the coordinates of the center of the corner
   * histogram cell, which are the lower bounds of the volume we care about.
   */
  minc0 = (c0 << BOX_C0_SHIFT) + ((1 << C0_SHIFT) >> 1);
  minc1 = (c1 << BOX_C1_SHIFT) + ((1 << C1_SHIFT) >> 1);
  minc2 = (c2 << BOX_C2_SHIFT) + ((1 << C2_SHIFT) >> 1);

  /* Determine which colormap entries are close enough to be candidates
   * for the nearest entry to some cell in the update box.
   */
  numcolors = find_nearby_colors(cinfo, minc0, minc1, minc2, colorlist);

  /* Determine the actually nearest colors. */
  find_best_colors(cinfo, minc0, minc1, minc2, numcolors, colorlist,
		   bestcolor);

  /* Save the best color numbers (plus 1) in the main cache array */
  c0 <<= BOX_C0_LOG;		/* convert ID back to base cell indexes */
  c1 <<= BOX_C1_LOG;
  c2 <<= BOX_C2_LOG;
  cptr = bestcolor;
  for (ic0 = 0; ic0 < BOX_C0_ELEMS; ic0++) {
    for (ic1 = 0; ic1 < BOX_C1_ELEMS; ic1++) {
      cachep = & histogram[c0+ic0][c1+ic1][c2];
      for (ic2 = 0; ic2 < BOX_C2_ELEMS; ic2++) {
	*cachep++ = (histcell) (GETJSAMPLE(*cptr++) + 1);
      }
    }
  }
}

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

METHODDEF(void)
pass2_no_dither (j_decompress_ptr cinfo,
		 JSAMPARRAY input_buf, JSAMPARRAY output_buf, int num_rows)
/* This version performs no dithering */
{
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  register JSAMPROW inptr, outptr;
  register histptr cachep;
  register int c0, c1, c2;
  int row;
  JDIMENSION col;
  JDIMENSION width = cinfo->output_width;

  for (row = 0; row < num_rows; row++) {
    inptr = input_buf[row];
    outptr = output_buf[row];
    for (col = width; col > 0; col--) {
      /* get pixel value and index into the cache */
      c0 = GETJSAMPLE(*inptr++) >> C0_SHIFT;
      c1 = GETJSAMPLE(*inptr++) >> C1_SHIFT;
      c2 = GETJSAMPLE(*inptr++) >> C2_SHIFT;
      cachep = & histogram[c0][c1][c2];
      /* If we have not seen this color before, find nearest colormap entry */
      /* and update the cache */
      if (*cachep == 0)
	fill_inverse_cmap(cinfo, c0,c1,c2);
      /* Now emit the colormap index for this cell */
      *outptr++ = (JSAMPLE) (*cachep - 1);
    }
  }
}

METHODDEF(void)
pass2_fs_dither (j_decompress_ptr cinfo,
		 JSAMPARRAY input_buf, JSAMPARRAY output_buf, int num_rows)
/* This version performs Floyd-Steinberg dithering */
{
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  register LOCFSERROR cur0, cur1, cur2;	/* current error or pixel value */
  LOCFSERROR belowerr0, belowerr1, belowerr2; /* error for pixel below cur */
  LOCFSERROR bpreverr0, bpreverr1, bpreverr2; /* error for below/prev col */
  register FSERRPTR errorptr;	/* => fserrors[] at column before current */
  JSAMPROW inptr;		/* => current input pixel */
  JSAMPROW outptr;		/* => current output pixel */
  histptr cachep;
  int dir;			/* +1 or -1 depending on direction */
  int dir3;			/* 3*dir, for advancing inptr & errorptr */
  int row;
  JDIMENSION col;
  JDIMENSION width = cinfo->output_width;
  JSAMPLE *range_limit = cinfo->sample_range_limit;
  int *error_limit = cquantize->error_limiter;
  JSAMPROW colormap0 = cinfo->colormap[0];
  JSAMPROW colormap1 = cinfo->colormap[1];
  JSAMPROW colormap2 = cinfo->colormap[2];
  SHIFT_TEMPS

  for (row = 0; row < num_rows; row++) {
    inptr = input_buf[row];
    outptr = output_buf[row];
    if (cquantize->on_odd_row) {
      /* work right to left in this row */
      inptr += (width-1) * 3;	/* so point to rightmost pixel */
      outptr += width-1;
      dir = -1;
      dir3 = -3;
      errorptr = cquantize->fserrors + (width+1)*3; /* => entry after last column */
      cquantize->on_odd_row = FALSE; /* flip for next time */
    } else {
      /* work left to right in this row */
      dir = 1;
      dir3 = 3;
      errorptr = cquantize->fserrors; /* => entry before first real column */
      cquantize->on_odd_row = TRUE; /* flip for next time */
    }
    /* Preset error values: no error propagated to first pixel from left */
    cur0 = cur1 = cur2 = 0;
    /* and no error propagated to row below yet */
    belowerr0 = belowerr1 = belowerr2 = 0;
    bpreverr0 = bpreverr1 = bpreverr2 = 0;

    for (col = width; col > 0; col--) {
      /* curN 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.
       */
      cur0 = RIGHT_SHIFT(cur0 + errorptr[dir3+0] + 8, 4);
      cur1 = RIGHT_SHIFT(cur1 + errorptr[dir3+1] + 8, 4);
      cur2 = RIGHT_SHIFT(cur2 + errorptr[dir3+2] + 8, 4);
      /* Limit the error using transfer function set by init_error_limit.
       * See comments with init_error_limit for rationale.
       */
      cur0 = error_limit[cur0];
      cur1 = error_limit[cur1];
      cur2 = error_limit[cur2];
      /* Form pixel value + error, and range-limit to 0..MAXJSAMPLE.
       * The maximum error is +- MAXJSAMPLE (or less with error limiting);
       * this sets the required size of the range_limit array.
       */
      cur0 += GETJSAMPLE(inptr[0]);
      cur1 += GETJSAMPLE(inptr[1]);
      cur2 += GETJSAMPLE(inptr[2]);
      cur0 = GETJSAMPLE(range_limit[cur0]);
      cur1 = GETJSAMPLE(range_limit[cur1]);
      cur2 = GETJSAMPLE(range_limit[cur2]);
      /* Index into the cache with adjusted pixel value */
      cachep = & histogram[cur0>>C0_SHIFT][cur1>>C1_SHIFT][cur2>>C2_SHIFT];
      /* If we have not seen this color before, find nearest colormap */
      /* entry and update the cache */
      if (*cachep == 0)
	fill_inverse_cmap(cinfo, cur0>>C0_SHIFT,cur1>>C1_SHIFT,cur2>>C2_SHIFT);
      /* Now emit the colormap index for this cell */
      { register int pixcode = *cachep - 1;
	*outptr = (JSAMPLE) pixcode;
	/* Compute representation error for this pixel */
	cur0 -= GETJSAMPLE(colormap0[pixcode]);
	cur1 -= GETJSAMPLE(colormap1[pixcode]);
	cur2 -= GETJSAMPLE(colormap2[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.
       */
      { register LOCFSERROR bnexterr, delta;

	bnexterr = cur0;	/* Process component 0 */
	delta = cur0 * 2;
	cur0 += delta;		/* form error * 3 */
	errorptr[0] = (FSERROR) (bpreverr0 + cur0);
	cur0 += delta;		/* form error * 5 */
	bpreverr0 = belowerr0 + cur0;
	belowerr0 = bnexterr;
	cur0 += delta;		/* form error * 7 */
	bnexterr = cur1;	/* Process component 1 */
	delta = cur1 * 2;
	cur1 += delta;		/* form error * 3 */
	errorptr[1] = (FSERROR) (bpreverr1 + cur1);
	cur1 += delta;		/* form error * 5 */
	bpreverr1 = belowerr1 + cur1;
	belowerr1 = bnexterr;
	cur1 += delta;		/* form error * 7 */
	bnexterr = cur2;	/* Process component 2 */
	delta = cur2 * 2;
	cur2 += delta;		/* form error * 3 */
	errorptr[2] = (FSERROR) (bpreverr2 + cur2);
	cur2 += delta;		/* form error * 5 */
	bpreverr2 = belowerr2 + cur2;
	belowerr2 = bnexterr;
	cur2 += delta;		/* form error * 7 */
      }
      /* At this point curN 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.
       */
      inptr += dir3;		/* Advance pixel pointers to next column */
      outptr += dir;
      errorptr += dir3;		/* advance errorptr to current column */
    }
    /* Post-loop cleanup: we must unload the final error values into the
     * final fserrors[] entry.  Note we need not unload belowerrN because
     * it is for the dummy column before or after the actual array.
     */
    errorptr[0] = (FSERROR) bpreverr0; /* unload prev errs into array */
    errorptr[1] = (FSERROR) bpreverr1;
    errorptr[2] = (FSERROR) bpreverr2;
  }
}

/*
 * Initialize the error-limiting transfer function (lookup table).
 * The raw F-S error computation can potentially compute error values of up to
 * +- MAXJSAMPLE.  But we want the maximum correction applied to a pixel to be
 * much less, otherwise obviously wrong pixels will be created.  (Typical
 * effects include weird fringes at color-area boundaries, isolated bright
 * pixels in a dark area, etc.)  The standard advice for avoiding this problem
 * is to ensure that the "corners" of the color cube are allocated as output
 * colors; then repeated errors in the same direction cannot cause cascading
 * error buildup.  However, that only prevents the error from getting
 * completely out of hand; Aaron Giles reports that error limiting improves
 * the results even with corner colors allocated.
 * A simple clamping of the error values to about +- MAXJSAMPLE/8 works pretty
 * well, but the smoother transfer function used below is even better.  Thanks
 * to Aaron Giles for this idea.
 */

LOCAL(void)
init_error_limit (j_decompress_ptr cinfo)
/* Allocate and fill in the error_limiter table */
{
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
  int * table;
  int in, out;

  table = (int *) (*cinfo->mem->alloc_small)
    ((j_common_ptr) cinfo, JPOOL_IMAGE, (MAXJSAMPLE*2+1) * SIZEOF(int));
  table += MAXJSAMPLE;		/* so can index -MAXJSAMPLE .. +MAXJSAMPLE */
  cquantize->error_limiter = table;

#define STEPSIZE ((MAXJSAMPLE+1)/16)
  /* Map errors 1:1 up to +- MAXJSAMPLE/16 */
  out = 0;
  for (in = 0; in < STEPSIZE; in++, out++) {
    table[in] = out; table[-in] = -out;
  }
  /* Map errors 1:2 up to +- 3*MAXJSAMPLE/16 */
  for (; in < STEPSIZE*3; in++, out += (in&1) ? 0 : 1) {
    table[in] = out; table[-in] = -out;
  }
  /* Clamp the rest to final out value (which is (MAXJSAMPLE+1)/8) */
  for (; in <= MAXJSAMPLE; in++) {
    table[in] = out; table[-in] = -out;
  }
#undef STEPSIZE
}

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

METHODDEF(void)
finish_pass1 (j_decompress_ptr cinfo)
{
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

  /* Select the representative colors and fill in cinfo->colormap */
  cinfo->colormap = cquantize->sv_colormap;
  select_colors(cinfo, cquantize->desired);
  /* Force next pass to zero the color index table */
  cquantize->needs_zeroed = TRUE;
}

METHODDEF(void)
finish_pass2 (j_decompress_ptr cinfo)
{
  /* no work */
}

/*
 * Initialize for each processing pass.
 */

METHODDEF(void)
start_pass_2_quant (j_decompress_ptr cinfo, boolean is_pre_scan)
{
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  int i;

  /* Only F-S dithering or no dithering is supported. */
  /* If user asks for ordered dither, give him F-S. */
  if (cinfo->dither_mode != JDITHER_NONE)
    cinfo->dither_mode = JDITHER_FS;

  if (is_pre_scan) {
    /* Set up method pointers */
    cquantize->pub.color_quantize = prescan_quantize;
    cquantize->pub.finish_pass = finish_pass1;
    cquantize->needs_zeroed = TRUE; /* Always zero histogram */
  } else {
    /* Set up method pointers */
    if (cinfo->dither_mode == JDITHER_FS)
      cquantize->pub.color_quantize = pass2_fs_dither;
    else
      cquantize->pub.color_quantize = pass2_no_dither;
    cquantize->pub.finish_pass = finish_pass2;

    /* Make sure color count is acceptable */
    i = cinfo->actual_number_of_colors;
    if (i < 1)
      ERREXIT1(cinfo, JERR_QUANT_FEW_COLORS, 1);
    if (i > MAXNUMCOLORS)
      ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXNUMCOLORS);

    if (cinfo->dither_mode == JDITHER_FS) {
      size_t arraysize = (size_t) ((cinfo->output_width + 2) *
				   (3 * SIZEOF(FSERROR)));
      /* Allocate Floyd-Steinberg workspace if we didn't already. */
      if (cquantize->fserrors == NULL)
	cquantize->fserrors = (FSERRPTR) (*cinfo->mem->alloc_large)
	  ((j_common_ptr) cinfo, JPOOL_IMAGE, arraysize);
      /* Initialize the propagated errors to zero. */
      jzero_far((void FAR *) cquantize->fserrors, arraysize);
      /* Make the error-limit table if we didn't already. */
      if (cquantize->error_limiter == NULL)
	init_error_limit(cinfo);
      cquantize->on_odd_row = FALSE;
    }

  }
  /* Zero the histogram or inverse color map, if necessary */
  if (cquantize->needs_zeroed) {
    for (i = 0; i < HIST_C0_ELEMS; i++) {
      jzero_far((void FAR *) histogram[i],
		HIST_C1_ELEMS*HIST_C2_ELEMS * SIZEOF(histcell));
    }
    cquantize->needs_zeroed = FALSE;
  }
}

/*
 * Switch to a new external colormap between output passes.
 */

METHODDEF(void)
new_color_map_2_quant (j_decompress_ptr cinfo)
{
  my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

  /* Reset the inverse color map */
  cquantize->needs_zeroed = TRUE;
}

/*
 * Module initialization routine for 2-pass color quantization.
 */

GLOBAL(void)
jinit_2pass_quantizer (j_decompress_ptr cinfo)
{
  my_cquantize_ptr cquantize;
  int i;

  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_2_quant;
  cquantize->pub.new_color_map = new_color_map_2_quant;
  cquantize->fserrors = NULL;	/* flag optional arrays not allocated */
  cquantize->error_limiter = NULL;

  /* Make sure jdmaster didn't give me a case I can't handle */
  if (cinfo->out_color_components != 3)
    ERREXIT(cinfo, JERR_NOTIMPL);

  /* Allocate the histogram/inverse colormap storage */
  cquantize->histogram = (hist3d) (*cinfo->mem->alloc_small)
    ((j_common_ptr) cinfo, JPOOL_IMAGE, HIST_C0_ELEMS * SIZEOF(hist2d));
  for (i = 0; i < HIST_C0_ELEMS; i++) {
    cquantize->histogram[i] = (hist2d) (*cinfo->mem->alloc_large)
      ((j_common_ptr) cinfo, JPOOL_IMAGE,
       HIST_C1_ELEMS*HIST_C2_ELEMS * SIZEOF(histcell));
  }
  cquantize->needs_zeroed = TRUE; /* histogram is garbage now */

  /* Allocate storage for the completed colormap, if required.
   * We do this now since it is FAR storage and may affect
   * the memory manager's space calculations.
   */
  if (cinfo->enable_2pass_quant) {
    /* Make sure color count is acceptable */
    int desired = cinfo->desired_number_of_colors;
    /* Lower bound on # of colors ... somewhat arbitrary as long as > 0 */
    if (desired < 8)
      ERREXIT1(cinfo, JERR_QUANT_FEW_COLORS, 8);
    /* Make sure colormap indexes can be represented by JSAMPLEs */
    if (desired > MAXNUMCOLORS)
      ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXNUMCOLORS);
    cquantize->sv_colormap = (*cinfo->mem->alloc_sarray)
      ((j_common_ptr) cinfo,JPOOL_IMAGE, (JDIMENSION) desired, (JDIMENSION) 3);
    cquantize->desired = desired;
  } else
    cquantize->sv_colormap = NULL;

  /* Only F-S dithering or no dithering is supported. */
  /* If user asks for ordered dither, give him F-S. */
  if (cinfo->dither_mode != JDITHER_NONE)
    cinfo->dither_mode = JDITHER_FS;

  /* Allocate Floyd-Steinberg workspace if necessary.
   * This isn't really needed until pass 2, but again it is FAR storage.
   * Although we will cope with a later change in dither_mode,
   * we do not promise to honor max_memory_to_use if dither_mode changes.
   */
  if (cinfo->dither_mode == JDITHER_FS) {
    cquantize->fserrors = (FSERRPTR) (*cinfo->mem->alloc_large)
      ((j_common_ptr) cinfo, JPOOL_IMAGE,
       (size_t) ((cinfo->output_width + 2) * (3 * SIZEOF(FSERROR))));
    /* Might as well create the error-limiting table too. */
    init_error_limit(cinfo);
  }
}

#endif /* QUANT_2PASS_SUPPORTED */


code:
/*
 * jutils.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 tables and miscellaneous utility routines needed
 * for both compression and decompression.
 * Note we prefix all global names with "j" to minimize conflicts with
 * a surrounding application.
 */

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

/*
 * jpeg_zigzag_order[i] is the zigzag-order position of the i'th element
 * of a DCT block read in natural order (left to right, top to bottom).
 */

#if 0				/* This table is not actually needed in v6a */

const int jpeg_zigzag_order[DCTSIZE2] = {
   0,  1,  5,  6, 14, 15, 27, 28,
   2,  4,  7, 13, 16, 26, 29, 42,
   3,  8, 12, 17, 25, 30, 41, 43,
   9, 11, 18, 24, 31, 40, 44, 53,
  10, 19, 23, 32, 39, 45, 52, 54,
  20, 22, 33, 38, 46, 51, 55, 60,
  21, 34, 37, 47, 50, 56, 59, 61,
  35, 36, 48, 49, 57, 58, 62, 63
};

#endif

/*
 * jpeg_natural_order[i] is the natural-order position of the i'th element
 * of zigzag order.
 *
 * When reading corrupted data, the Huffman decoders could attempt
 * to reference an entry beyond the end of this array (if the decoded
 * zero run length reaches past the end of the block).  To prevent
 * wild stores without adding an inner-loop test, we put some extra
 * "63"s after the real entries.  This will cause the extra coefficient
 * to be stored in location 63 of the block, not somewhere random.
 * The worst case would be a run-length of 15, which means we need 16
 * fake entries.
 */

const int jpeg_natural_order[DCTSIZE2+16] = {
  0,  1,  8, 16,  9,  2,  3, 10,
 17, 24, 32, 25, 18, 11,  4,  5,
 12, 19, 26, 33, 40, 48, 41, 34,
 27, 20, 13,  6,  7, 14, 21, 28,
 35, 42, 49, 56, 57, 50, 43, 36,
 29, 22, 15, 23, 30, 37, 44, 51,
 58, 59, 52, 45, 38, 31, 39, 46,
 53, 60, 61, 54, 47, 55, 62, 63,
 63, 63, 63, 63, 63, 63, 63, 63, /* extra entries for safety in decoder */
 63, 63, 63, 63, 63, 63, 63, 63
};

/*
 * Arithmetic utilities
 */

GLOBAL(long)
jdiv_round_up (long a, long b)
/* Compute a/b rounded up to next integer, ie, ceil(a/b) */
/* Assumes a >= 0, b > 0 */
{
  return (a + b - 1L) / b;
}

GLOBAL(long)
jround_up (long a, long b)
/* Compute a rounded up to next multiple of b, ie, ceil(a/b)*b */
/* Assumes a >= 0, b > 0 */
{
  a += b - 1L;
  return a - (a % b);
}

/* On normal machines we can apply MEMCOPY() and MEMZERO() to sample arrays
 * and coefficient-block arrays.  This won't work on 80x86 because the arrays
 * are FAR and we're assuming a small-pointer memory model.  However, some
 * DOS compilers provide far-pointer versions of memcpy() and memset() even
 * in the small-model libraries.  These will be used if USE_FMEM is defined.
 * Otherwise, the routines below do it the hard way.  (The performance cost
 * is not all that great, because these routines aren't very heavily used.)
 */

#ifndef NEED_FAR_POINTERS	/* normal case, same as regular macros */
#define FMEMCOPY(dest,src,size)	MEMCOPY(dest,src,size)
#define FMEMZERO(target,size)	MEMZERO(target,size)
#else				/* 80x86 case, define if we can */
#ifdef USE_FMEM
#define FMEMCOPY(dest,src,size)	_fmemcpy((void FAR *)(dest), (const void FAR *)(src), (size_t)(size))
#define FMEMZERO(target,size)	_fmemset((void FAR *)(target), 0, (size_t)(size))
#endif
#endif

GLOBAL(void)
jcopy_sample_rows (JSAMPARRAY input_array, int source_row,
		   JSAMPARRAY output_array, int dest_row,
		   int num_rows, JDIMENSION num_cols)
/* Copy some rows of samples from one place to another.
 * num_rows rows are copied from input_array[source_row++]
 * to output_array[dest_row++]; these areas may overlap for duplication.
 * The source and destination arrays must be at least as wide as num_cols.
 */
{
  register JSAMPROW inptr, outptr;
#ifdef FMEMCOPY
  register size_t count = (size_t) (num_cols * SIZEOF(JSAMPLE));
#else
  register JDIMENSION count;
#endif
  register int row;

  input_array += source_row;
  output_array += dest_row;

  for (row = num_rows; row > 0; row--) {
    inptr = *input_array++;
    outptr = *output_array++;
#ifdef FMEMCOPY
    FMEMCOPY(outptr, inptr, count);
#else
    for (count = num_cols; count > 0; count--)
      *outptr++ = *inptr++;	/* needn't bother with GETJSAMPLE() here */
#endif
  }
}

GLOBAL(void)
jcopy_block_row (JBLOCKROW input_row, JBLOCKROW output_row,
		 JDIMENSION num_blocks)
/* Copy a row of coefficient blocks from one place to another. */
{
#ifdef FMEMCOPY
  FMEMCOPY(output_row, input_row, num_blocks * (DCTSIZE2 * SIZEOF(JCOEF)));
#else
  register JCOEFPTR inptr, outptr;
  register long count;

  inptr = (JCOEFPTR) input_row;
  outptr = (JCOEFPTR) output_row;
  for (count = (long) num_blocks * DCTSIZE2; count > 0; count--) {
    *outptr++ = *inptr++;
  }
#endif
}

GLOBAL(void)
jzero_far (void FAR * target, size_t bytestozero)
/* Zero out a chunk of FAR memory. */
/* This might be sample-array data, block-array data, or alloc_large data. */
{
#ifdef FMEMZERO
  FMEMZERO(target, bytestozero);
#else
  register char FAR * ptr = (char FAR *) target;
  register size_t count;

  for (count = bytestozero; count > 0; count--) {
    *ptr++ = 0;
  }
#endif
}

license: mit


code:
/*
 * jversion.h
 *
 * Copyright (C) 1991-1998, 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 software version identification.
 */

#define JVERSION	"6b  27-Mar-1998"

#define JCOPYRIGHT	"Copyright (C) 1998, Thomas G. Lane"


code:
/*
 * rdbmp.c
 *
 * Copyright (C) 1994-1996, 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 routines to read input images in Microsoft "BMP"
 * format (MS Windows 3.x, OS/2 1.x, and OS/2 2.x flavors).
 * Currently, only 8-bit and 24-bit images are supported, not 1-bit or
 * 4-bit (feeding such low-depth images into JPEG would be silly anyway).
 * Also, we don't support RLE-compressed files.
 *
 * These routines may need modification for non-Unix environments or
 * specialized applications.  As they stand, they assume input from
 * an ordinary stdio stream.  They further assume that reading begins
 * at the start of the file; start_input may need work if the
 * user interface has already read some data (e.g., to determine that
 * the file is indeed BMP format).
 *
 * This code contributed by James Arthur Boucher.
 */

#include "cdjpeg.h"		/* Common decls for cjpeg/djpeg applications */

#ifdef BMP_SUPPORTED

/* Macros to deal with unsigned chars as efficiently as compiler allows */

#ifdef HAVE_UNSIGNED_CHAR
typedef unsigned char U_CHAR;
#define UCH(x)	((int) (x))
#else /* !HAVE_UNSIGNED_CHAR */
#ifdef CHAR_IS_UNSIGNED
typedef char U_CHAR;
#define UCH(x)	((int) (x))
#else
typedef char U_CHAR;
#define UCH(x)	((int) (x) & 0xFF)
#endif
#endif /* HAVE_UNSIGNED_CHAR */

#define	ReadOK(file,buffer,len)	(JFREAD(file,buffer,len) == ((size_t) (len)))

/* Private version of data source object */

typedef struct _bmp_source_struct * bmp_source_ptr;

typedef struct _bmp_source_struct {
  struct cjpeg_source_struct pub; /* public fields */

  j_compress_ptr cinfo;		/* back link saves passing separate parm */

  JSAMPARRAY colormap;		/* BMP colormap (converted to my format) */

  jvirt_sarray_ptr whole_image;	/* Needed to reverse row order */
  JDIMENSION source_row;	/* Current source row number */
  JDIMENSION row_width;		/* Physical width of scanlines in file */

  int bits_per_pixel;		/* remembers 8- or 24-bit format */
} bmp_source_struct;

LOCAL(int)
read_byte (bmp_source_ptr sinfo)
/* Read next byte from BMP file */
{
  register FILE *infile = sinfo->pub.input_file;
  register int c;

  if ((c = getc(infile)) == EOF)
    ERREXIT(sinfo->cinfo, JERR_INPUT_EOF);
  return c;
}

LOCAL(void)
read_colormap (bmp_source_ptr sinfo, int cmaplen, int mapentrysize)
/* Read the colormap from a BMP file */
{
  int i;

  switch (mapentrysize) {
  case 3:
    /* BGR format (occurs in OS/2 files) */
    for (i = 0; i < cmaplen; i++) {
      sinfo->colormap[2][i] = (JSAMPLE) read_byte(sinfo);
      sinfo->colormap[1][i] = (JSAMPLE) read_byte(sinfo);
      sinfo->colormap[0][i] = (JSAMPLE) read_byte(sinfo);
    }
    break;
  case 4:
    /* BGR0 format (occurs in MS Windows files) */
    for (i = 0; i < cmaplen; i++) {
      sinfo->colormap[2][i] = (JSAMPLE) read_byte(sinfo);
      sinfo->colormap[1][i] = (JSAMPLE) read_byte(sinfo);
      sinfo->colormap[0][i] = (JSAMPLE) read_byte(sinfo);
      (void) read_byte(sinfo);
    }
    break;
  default:
    ERREXIT(sinfo->cinfo, JERR_BMP_BADCMAP);
    break;
  }
}

/*
 * Read one row of pixels.
 * The image has been read into the whole_image array, but is otherwise
 * unprocessed.  We must read it out in top-to-bottom row order, and if
 * it is an 8-bit image, we must expand colormapped pixels to 24bit format.
 */

METHODDEF(JDIMENSION)
get_8bit_row (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)
/* This version is for reading 8-bit colormap indexes */
{
  bmp_source_ptr source = (bmp_source_ptr) sinfo;
  register JSAMPARRAY colormap = source->colormap;
  JSAMPARRAY image_ptr;
  register int t;
  register JSAMPROW inptr, outptr;
  register JDIMENSION col;

  /* Fetch next row from virtual array */
  source->source_row--;
  image_ptr = (*cinfo->mem->access_virt_sarray)
    ((j_common_ptr) cinfo, source->whole_image,
     source->source_row, (JDIMENSION) 1, FALSE);

  /* Expand the colormap indexes to real data */
  inptr = image_ptr[0];
  outptr = source->pub.buffer[0];
  for (col = cinfo->image_width; col > 0; col--) {
    t = GETJSAMPLE(*inptr++);
    *outptr++ = colormap[0][t];	/* can omit GETJSAMPLE() safely */
    *outptr++ = colormap[1][t];
    *outptr++ = colormap[2][t];
  }

  return 1;
}

METHODDEF(JDIMENSION)
get_24bit_row (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)
/* This version is for reading 24-bit pixels */
{
  bmp_source_ptr source = (bmp_source_ptr) sinfo;
  JSAMPARRAY image_ptr;
  register JSAMPROW inptr, outptr;
  register JDIMENSION col;

  /* Fetch next row from virtual array */
  source->source_row--;
  image_ptr = (*cinfo->mem->access_virt_sarray)
    ((j_common_ptr) cinfo, source->whole_image,
     source->source_row, (JDIMENSION) 1, FALSE);

  /* Transfer data.  Note source values are in BGR order
   * (even though Microsoft's own documents say the opposite).
   */
  inptr = image_ptr[0];
  outptr = source->pub.buffer[0];
  for (col = cinfo->image_width; col > 0; col--) {
    outptr[2] = *inptr++;	/* can omit GETJSAMPLE() safely */
    outptr[1] = *inptr++;
    outptr[0] = *inptr++;
    outptr += 3;
  }

  return 1;
}

/*
 * This method loads the image into whole_image during the first call on
 * get_pixel_rows.  The get_pixel_rows pointer is then adjusted to call
 * get_8bit_row or get_24bit_row on subsequent calls.
 */

METHODDEF(JDIMENSION)
preload_image (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)
{
  bmp_source_ptr source = (bmp_source_ptr) sinfo;
  register FILE *infile = source->pub.input_file;
  register int c;
  register JSAMPROW out_ptr;
  JSAMPARRAY image_ptr;
  JDIMENSION row, col;
  cd_progress_ptr progress = (cd_progress_ptr) cinfo->progress;

  /* Read the data into a virtual array in input-file row order. */
  for (row = 0; row < cinfo->image_height; row++) {
    if (progress != NULL) {
      progress->pub.pass_counter = (long) row;
      progress->pub.pass_limit = (long) cinfo->image_height;
      (*progress->pub.progress_monitor) ((j_common_ptr) cinfo);
    }
    image_ptr = (*cinfo->mem->access_virt_sarray)
      ((j_common_ptr) cinfo, source->whole_image,
       row, (JDIMENSION) 1, TRUE);
    out_ptr = image_ptr[0];
    for (col = source->row_width; col > 0; col--) {
      /* inline copy of read_byte() for speed */
      if ((c = getc(infile)) == EOF)
	ERREXIT(cinfo, JERR_INPUT_EOF);
      *out_ptr++ = (JSAMPLE) c;
    }
  }
  if (progress != NULL)
    progress->completed_extra_passes++;

  /* Set up to read from the virtual array in top-to-bottom order */
  switch (source->bits_per_pixel) {
  case 8:
    source->pub.get_pixel_rows = get_8bit_row;
    break;
  case 24:
    source->pub.get_pixel_rows = get_24bit_row;
    break;
  default:
    ERREXIT(cinfo, JERR_BMP_BADDEPTH);
  }
  source->source_row = cinfo->image_height;

  /* And read the first row */
  return (*source->pub.get_pixel_rows) (cinfo, sinfo);
}

/*
 * Read the file header; return image size and component count.
 */

METHODDEF(void)
start_input_bmp (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)
{
  bmp_source_ptr source = (bmp_source_ptr) sinfo;
  U_CHAR bmpfileheader[14];
  U_CHAR bmpinfoheader[64];
#define GET_2B(array,offset)  ((unsigned int) UCH(array[offset]) + \
			       (((unsigned int) UCH(array[offset+1])) << 8))
#define GET_4B(array,offset)  ((INT32) UCH(array[offset]) + \
			       (((INT32) UCH(array[offset+1])) << 8) + \
			       (((INT32) UCH(array[offset+2])) << 16) + \
			       (((INT32) UCH(array[offset+3])) << 24))
  INT32 bfOffBits;
  INT32 headerSize;
  INT32 biWidth = 0;		/* initialize to avoid compiler warning */
  INT32 biHeight = 0;
  unsigned int biPlanes;
  INT32 biCompression;
  INT32 biXPelsPerMeter,biYPelsPerMeter;
  INT32 biClrUsed = 0;
  int mapentrysize = 0;		/* 0 indicates no colormap */
  INT32 bPad;
  JDIMENSION row_width;

  /* Read and verify the bitmap file header */
  if (! ReadOK(source->pub.input_file, bmpfileheader, 14))
    ERREXIT(cinfo, JERR_INPUT_EOF);
  if (GET_2B(bmpfileheader,0) != 0x4D42) /* 'BM' */
    ERREXIT(cinfo, JERR_BMP_NOT);
  bfOffBits = (INT32) GET_4B(bmpfileheader,10);
  /* We ignore the remaining fileheader fields */

  /* The infoheader might be 12 bytes (OS/2 1.x), 40 bytes (Windows),
   * or 64 bytes (OS/2 2.x).  Check the first 4 bytes to find out which.
   */
  if (! ReadOK(source->pub.input_file, bmpinfoheader, 4))
    ERREXIT(cinfo, JERR_INPUT_EOF);
  headerSize = (INT32) GET_4B(bmpinfoheader,0);
  if (headerSize < 12 || headerSize > 64)
    ERREXIT(cinfo, JERR_BMP_BADHEADER);
  if (! ReadOK(source->pub.input_file, bmpinfoheader+4, headerSize-4))
    ERREXIT(cinfo, JERR_INPUT_EOF);

  switch ((int) headerSize) {
  case 12:
    /* Decode OS/2 1.x header (Microsoft calls this a BITMAPCOREHEADER) */
    biWidth = (INT32) GET_2B(bmpinfoheader,4);
    biHeight = (INT32) GET_2B(bmpinfoheader,6);
    biPlanes = GET_2B(bmpinfoheader,8);
    source->bits_per_pixel = (int) GET_2B(bmpinfoheader,10);

    switch (source->bits_per_pixel) {
    case 8:			/* colormapped image */
      mapentrysize = 3;		/* OS/2 uses RGBTRIPLE colormap */
      TRACEMS2(cinfo, 1, JTRC_BMP_OS2_MAPPED, (int) biWidth, (int) biHeight);
      break;
    case 24:			/* RGB image */
      TRACEMS2(cinfo, 1, JTRC_BMP_OS2, (int) biWidth, (int) biHeight);
      break;
    default:
      ERREXIT(cinfo, JERR_BMP_BADDEPTH);
      break;
    }
    if (biPlanes != 1)
      ERREXIT(cinfo, JERR_BMP_BADPLANES);
    break;
  case 40:
  case 64:
    /* Decode Windows 3.x header (Microsoft calls this a BITMAPINFOHEADER) */
    /* or OS/2 2.x header, which has additional fields that we ignore */
    biWidth = GET_4B(bmpinfoheader,4);
    biHeight = GET_4B(bmpinfoheader,8);
    biPlanes = GET_2B(bmpinfoheader,12);
    source->bits_per_pixel = (int) GET_2B(bmpinfoheader,14);
    biCompression = GET_4B(bmpinfoheader,16);
    biXPelsPerMeter = GET_4B(bmpinfoheader,24);
    biYPelsPerMeter = GET_4B(bmpinfoheader,28);
    biClrUsed = GET_4B(bmpinfoheader,32);
    /* biSizeImage, biClrImportant fields are ignored */

    switch (source->bits_per_pixel) {
    case 8:			/* colormapped image */
      mapentrysize = 4;		/* Windows uses RGBQUAD colormap */
      TRACEMS2(cinfo, 1, JTRC_BMP_MAPPED, (int) biWidth, (int) biHeight);
      break;
    case 24:			/* RGB image */
      TRACEMS2(cinfo, 1, JTRC_BMP, (int) biWidth, (int) biHeight);
      break;
    default:
      ERREXIT(cinfo, JERR_BMP_BADDEPTH);
      break;
    }
    if (biPlanes != 1)
      ERREXIT(cinfo, JERR_BMP_BADPLANES);
    if (biCompression != 0)
      ERREXIT(cinfo, JERR_BMP_COMPRESSED);

    if (biXPelsPerMeter > 0 && biYPelsPerMeter > 0) {
      /* Set JFIF density parameters from the BMP data */
      cinfo->X_density = (UINT16) (biXPelsPerMeter/100); /* 100 cm per meter */
      cinfo->Y_density = (UINT16) (biYPelsPerMeter/100);
      cinfo->density_unit = 2;	/* dots/cm */
    }
    break;
  default:
    ERREXIT(cinfo, JERR_BMP_BADHEADER);
    break;
  }

  /* Compute distance to bitmap data --- will adjust for colormap below */
  bPad = bfOffBits - (headerSize + 14);

  /* Read the colormap, if any */
  if (mapentrysize > 0) {
    if (biClrUsed <= 0)
      biClrUsed = 256;		/* assume it's 256 */
    else if (biClrUsed > 256)
      ERREXIT(cinfo, JERR_BMP_BADCMAP);
    /* Allocate space to store the colormap */
    source->colormap = (*cinfo->mem->alloc_sarray)
      ((j_common_ptr) cinfo, JPOOL_IMAGE,
       (JDIMENSION) biClrUsed, (JDIMENSION) 3);
    /* and read it from the file */
    read_colormap(source, (int) biClrUsed, mapentrysize);
    /* account for size of colormap */
    bPad -= biClrUsed * mapentrysize;
  }

  /* Skip any remaining pad bytes */
  if (bPad < 0)			/* incorrect bfOffBits value? */
    ERREXIT(cinfo, JERR_BMP_BADHEADER);
  while (--bPad >= 0) {
    (void) read_byte(source);
  }

  /* Compute row width in file, including padding to 4-byte boundary */
  if (source->bits_per_pixel == 24)
    row_width = (JDIMENSION) (biWidth * 3);
  else
    row_width = (JDIMENSION) biWidth;
  while ((row_width & 3) != 0) row_width++;
  source->row_width = row_width;

  /* Allocate space for inversion array, prepare for preload pass */
  source->whole_image = (*cinfo->mem->request_virt_sarray)
    ((j_common_ptr) cinfo, JPOOL_IMAGE, FALSE,
     row_width, (JDIMENSION) biHeight, (JDIMENSION) 1);
  source->pub.get_pixel_rows = preload_image;
  if (cinfo->progress != NULL) {
    cd_progress_ptr progress = (cd_progress_ptr) cinfo->progress;
    progress->total_extra_passes++; /* count file input as separate pass */
  }

  /* Allocate one-row buffer for returned data */
  source->pub.buffer = (*cinfo->mem->alloc_sarray)
    ((j_common_ptr) cinfo, JPOOL_IMAGE,
     (JDIMENSION) (biWidth * 3), (JDIMENSION) 1);
  source->pub.buffer_height = 1;

  cinfo->in_color_space = JCS_RGB;
  cinfo->input_components = 3;
  cinfo->data_precision = 8;
  cinfo->image_width = (JDIMENSION) biWidth;
  cinfo->image_height = (JDIMENSION) biHeight;
}

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

METHODDEF(void)
finish_input_bmp (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)
{
  /* no work */
}

/*
 * The module selection routine for BMP format input.
 */

GLOBAL(cjpeg_source_ptr)
jinit_read_bmp (j_compress_ptr cinfo)
{
  bmp_source_ptr source;

  /* Create module interface object */
  source = (bmp_source_ptr)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
				  SIZEOF(bmp_source_struct));
  source->cinfo = cinfo;	/* make back link for subroutines */
  /* Fill in method ptrs, except get_pixel_rows which start_input sets */
  source->pub.start_input = start_input_bmp;
  source->pub.finish_input = finish_input_bmp;

  return (cjpeg_source_ptr) source;
}

#endif /* BMP_SUPPORTED */


code:
/*
 * rdcolmap.c
 *
 * Copyright (C) 1994-1996, 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 implements djpeg's "-map file" switch.  It reads a source image
 * and constructs a colormap to be supplied to the JPEG decompressor.
 *
 * Currently, these file formats are supported for the map file:
 *   GIF: the contents of the GIF's global colormap are used.
 *   PPM (either text or raw flavor): the entire file is read and
 *      each unique pixel value is entered in the map.
 * Note that reading a large PPM file will be horrendously slow.
 * Typically, a PPM-format map file should contain just one pixel
 * of each desired color.  Such a file can be extracted from an
 * ordinary image PPM file with ppmtomap(1).
 *
 * Rescaling a PPM that has a maxval unequal to MAXJSAMPLE is not
 * currently implemented.
 */

#include "cdjpeg.h"		/* Common decls for cjpeg/djpeg applications */

#ifdef QUANT_2PASS_SUPPORTED	/* otherwise can't quantize to supplied map */

/* Portions of this code are based on the PBMPLUS library, which is:
**
** Copyright (C) 1988 by Jef Poskanzer.
**
** Permission to use, copy, modify, and distribute this software and its
** documentation for any purpose and without fee is hereby granted, provided
** that the above copyright notice appear in all copies and that both that
** copyright notice and this permission notice appear in supporting
** documentation.  This software is provided "as is" without express or
** implied warranty.
*/

/*
 * Add a (potentially) new color to the color map.
 */

LOCAL(void)
add_map_entry (j_decompress_ptr cinfo, int R, int G, int B)
{
  JSAMPROW colormap0 = cinfo->colormap[0];
  JSAMPROW colormap1 = cinfo->colormap[1];
  JSAMPROW colormap2 = cinfo->colormap[2];
  int ncolors = cinfo->actual_number_of_colors;
  int index;

  /* Check for duplicate color. */
  for (index = 0; index < ncolors; index++) {
    if (GETJSAMPLE(colormap0[index]) == R &&
	GETJSAMPLE(colormap1[index]) == G &&
	GETJSAMPLE(colormap2[index]) == B)
      return;			/* color is already in map */
  }

  /* Check for map overflow. */
  if (ncolors >= (MAXJSAMPLE+1))
    ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, (MAXJSAMPLE+1));

  /* OK, add color to map. */
  colormap0[ncolors] = (JSAMPLE) R;
  colormap1[ncolors] = (JSAMPLE) G;
  colormap2[ncolors] = (JSAMPLE) B;
  cinfo->actual_number_of_colors++;
}

/*
 * Extract color map from a GIF file.
 */

LOCAL(void)
read_gif_map (j_decompress_ptr cinfo, FILE * infile)
{
  int header[13];
  int i, colormaplen;
  int R, G, B;

  /* Initial 'G' has already been read by read_color_map */
  /* Read the rest of the GIF header and logical screen descriptor */
  for (i = 1; i < 13; i++) {
    if ((header[i] = getc(infile)) == EOF)
      ERREXIT(cinfo, JERR_BAD_CMAP_FILE);
  }

  /* Verify GIF Header */
  if (header[1] != 'I' || header[2] != 'F')
    ERREXIT(cinfo, JERR_BAD_CMAP_FILE);

  /* There must be a global color map. */
  if ((header[10] & 0x80) == 0)
    ERREXIT(cinfo, JERR_BAD_CMAP_FILE);

  /* OK, fetch it. */
  colormaplen = 2 << (header[10] & 0x07);

  for (i = 0; i < colormaplen; i++) {
    R = getc(infile);
    G = getc(infile);
    B = getc(infile);
    if (R == EOF || G == EOF || B == EOF)
      ERREXIT(cinfo, JERR_BAD_CMAP_FILE);
    add_map_entry(cinfo,
		  R << (BITS_IN_JSAMPLE-8),
		  G << (BITS_IN_JSAMPLE-8),
		  B << (BITS_IN_JSAMPLE-8));
  }
}

/* Support routines for reading PPM */

LOCAL(int)
pbm_getc (FILE * infile)
/* Read next char, skipping over any comments */
/* A comment/newline sequence is returned as a newline */
{
  register int ch;

  ch = getc(infile);
  if (ch == '#') {
    do {
      ch = getc(infile);
    } while (ch != '\n' && ch != EOF);
  }
  return ch;
}

LOCAL(unsigned int)
read_pbm_integer (j_decompress_ptr cinfo, FILE * infile)
/* Read an unsigned decimal integer from the PPM file */
/* Swallows one trailing character after the integer */
/* Note that on a 16-bit-int machine, only values up to 64k can be read. */
/* This should not be a problem in practice. */
{
  register int ch;
  register unsigned int val;

  /* Skip any leading whitespace */
  do {
    ch = pbm_getc(infile);
    if (ch == EOF)
      ERREXIT(cinfo, JERR_BAD_CMAP_FILE);
  } while (ch == ' ' || ch == '\t' || ch == '\n' || ch == '\r');

  if (ch < '0' || ch > '9')
    ERREXIT(cinfo, JERR_BAD_CMAP_FILE);

  val = ch - '0';
  while ((ch = pbm_getc(infile)) >= '0' && ch <= '9') {
    val *= 10;
    val += ch - '0';
  }
  return val;
}

/*
 * Extract color map from a PPM file.
 */

LOCAL(void)
read_ppm_map (j_decompress_ptr cinfo, FILE * infile)
{
  int c;
  unsigned int w, h, maxval, row, col;
  int R, G, B;

  /* Initial 'P' has already been read by read_color_map */
  c = getc(infile);		/* save format discriminator for a sec */

  /* while we fetch the remaining header info */
  w = read_pbm_integer(cinfo, infile);
  h = read_pbm_integer(cinfo, infile);
  maxval = read_pbm_integer(cinfo, infile);

  if (w <= 0 || h <= 0 || maxval <= 0) /* error check */
    ERREXIT(cinfo, JERR_BAD_CMAP_FILE);

  /* For now, we don't support rescaling from an unusual maxval. */
  if (maxval != (unsigned int) MAXJSAMPLE)
    ERREXIT(cinfo, JERR_BAD_CMAP_FILE);

  switch (c) {
  case '3':			/* it's a text-format PPM file */
    for (row = 0; row < h; row++) {
      for (col = 0; col < w; col++) {
	R = read_pbm_integer(cinfo, infile);
	G = read_pbm_integer(cinfo, infile);
	B = read_pbm_integer(cinfo, infile);
	add_map_entry(cinfo, R, G, B);
      }
    }
    break;

  case '6':			/* it's a raw-format PPM file */
    for (row = 0; row < h; row++) {
      for (col = 0; col < w; col++) {
	R = getc(infile);
	G = getc(infile);
	B = getc(infile);
	if (R == EOF || G == EOF || B == EOF)
	  ERREXIT(cinfo, JERR_BAD_CMAP_FILE);
	add_map_entry(cinfo, R, G, B);
      }
    }
    break;

  default:
    ERREXIT(cinfo, JERR_BAD_CMAP_FILE);
    break;
  }
}

/*
 * Main entry point from djpeg.c.
 *  Input: opened input file (from file name argument on command line).
 *  Output: colormap and actual_number_of_colors fields are set in cinfo.
 */

GLOBAL(void)
read_color_map (j_decompress_ptr cinfo, FILE * infile)
{
  /* Allocate space for a color map of maximum supported size. */
  cinfo->colormap = (*cinfo->mem->alloc_sarray)
    ((j_common_ptr) cinfo, JPOOL_IMAGE,
     (JDIMENSION) (MAXJSAMPLE+1), (JDIMENSION) 3);
  cinfo->actual_number_of_colors = 0; /* initialize map to empty */

  /* Read first byte to determine file format */
  switch (getc(infile)) {
  case 'G':
    read_gif_map(cinfo, infile);
    break;
  case 'P':
    read_ppm_map(cinfo, infile);
    break;
  default:
    ERREXIT(cinfo, JERR_BAD_CMAP_FILE);
    break;
  }
}

#endif /* QUANT_2PASS_SUPPORTED */


code:
/*
 * rdgif.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 routines to read input images in GIF format.
 *
 *****************************************************************************
 * NOTE: to avoid entanglements with Unisys' patent on LZW compression,      *
 * the ability to read GIF files has been removed from the IJG distribution. *
 * Sorry about that.                                                         *
 *****************************************************************************
 *
 * We are required to state that
 *    "The Graphics Interchange Format(c) is the Copyright property of
 *    CompuServe Incorporated. GIF(sm) is a Service Mark property of
 *    CompuServe Incorporated."
 */

#include "cdjpeg.h"		/* Common decls for cjpeg/djpeg applications */

#ifdef GIF_SUPPORTED

/*
 * The module selection routine for GIF format input.
 */

GLOBAL(cjpeg_source_ptr)
jinit_read_gif (j_compress_ptr cinfo)
{
  fprintf(stderr, "GIF input is unsupported for legal reasons.  Sorry.\n");
  exit(EXIT_FAILURE);
  return NULL;			/* keep compiler happy */
}

#endif /* GIF_SUPPORTED */


code:
/*
 * rdjpgcom.c
 *
 * Copyright (C) 1994-1997, 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 a very simple stand-alone application that displays
 * the text in COM (comment) markers in a JFIF file.
 * This may be useful as an example of the minimum logic needed to parse
 * JPEG markers.
 */

#define JPEG_CJPEG_DJPEG	/* to get the command-line config symbols */
#include "jinclude.h"		/* get auto-config symbols, <stdio.h> */

#include <ctype.h>		/* to declare isupper(), tolower() */
#ifdef USE_SETMODE
#include <fcntl.h>		/* to declare setmode()'s parameter macros */
/* If you have setmode() but not <io.h>, just delete this line: */
#include <io.h>			/* to declare setmode() */
#endif

#ifdef USE_CCOMMAND		/* command-line reader for Macintosh */
#ifdef __MWERKS__
#include <SIOUX.h>              /* Metrowerks needs this */
#include <console.h>		/* ... and this */
#endif
#ifdef THINK_C
#include <console.h>		/* Think declares it here */
#endif
#endif

#ifdef DONT_USE_B_MODE		/* define mode parameters for fopen() */
#define READ_BINARY	"r"
#else
#ifdef VMS			/* VMS is very nonstandard */
#define READ_BINARY	"rb", "ctx=stm"
#else				/* standard ANSI-compliant case */
#define READ_BINARY	"rb"
#endif
#endif

#ifndef EXIT_FAILURE		/* define exit() codes if not provided */
#define EXIT_FAILURE  1
#endif
#ifndef EXIT_SUCCESS
#ifdef VMS
#define EXIT_SUCCESS  1		/* VMS is very nonstandard */
#else
#define EXIT_SUCCESS  0
#endif
#endif

/*
 * These macros are used to read the input file.
 * To reuse this code in another application, you might need to change these.
 */

static FILE * infile;		/* input JPEG file */

/* Return next input byte, or EOF if no more */
#define NEXTBYTE()  getc(infile)

/* Error exit handler */
#define ERREXIT(msg)  (fprintf(stderr, "%s\n", msg), exit(EXIT_FAILURE))

/* Read one byte, testing for EOF */
static int
read_1_byte (void)
{
  int c;

  c = NEXTBYTE();
  if (c == EOF)
    ERREXIT("Premature EOF in JPEG file");
  return c;
}

/* Read 2 bytes, convert to unsigned int */
/* All 2-byte quantities in JPEG markers are MSB first */
static unsigned int
read_2_bytes (void)
{
  int c1, c2;

  c1 = NEXTBYTE();
  if (c1 == EOF)
    ERREXIT("Premature EOF in JPEG file");
  c2 = NEXTBYTE();
  if (c2 == EOF)
    ERREXIT("Premature EOF in JPEG file");
  return (((unsigned int) c1) << 8) + ((unsigned int) c2);
}

/*
 * JPEG markers consist of one or more 0xFF bytes, followed by a marker
 * code byte (which is not an FF).  Here are the marker codes of interest
 * in this program.  (See jdmarker.c for a more complete list.)
 */

#define M_SOF0  0xC0		/* Start Of Frame N */
#define M_SOF1  0xC1		/* N indicates which compression process */
#define M_SOF2  0xC2		/* Only SOF0-SOF2 are now in common use */
#define M_SOF3  0xC3
#define M_SOF5  0xC5		/* NB: codes C4 and CC are NOT SOF markers */
#define M_SOF6  0xC6
#define M_SOF7  0xC7
#define M_SOF9  0xC9
#define M_SOF10 0xCA
#define M_SOF11 0xCB
#define M_SOF13 0xCD
#define M_SOF14 0xCE
#define M_SOF15 0xCF
#define M_SOI   0xD8		/* Start Of Image (beginning of datastream) */
#define M_EOI   0xD9		/* End Of Image (end of datastream) */
#define M_SOS   0xDA		/* Start Of Scan (begins compressed data) */
#define M_APP0	0xE0		/* Application-specific marker, type N */
#define M_APP12	0xEC		/* (we don't bother to list all 16 APPn's) */
#define M_COM   0xFE		/* COMment */

/*
 * Find the next JPEG marker and return its marker code.
 * We expect at least one FF byte, possibly more if the compressor used FFs
 * to pad the file.
 * There could also be non-FF garbage between markers.  The treatment of such
 * garbage is unspecified; we choose to skip over it but emit a warning msg.
 * NB: this routine must not be used after seeing SOS marker, since it will
 * not deal correctly with FF/00 sequences in the compressed image data...
 */

static int
next_marker (void)
{
  int c;
  int discarded_bytes = 0;

  /* Find 0xFF byte; count and skip any non-FFs. */
  c = read_1_byte();
  while (c != 0xFF) {
    discarded_bytes++;
    c = read_1_byte();
  }
  /* Get marker code byte, swallowing any duplicate FF bytes.  Extra FFs
   * are legal as pad bytes, so don't count them in discarded_bytes.
   */
  do {
    c = read_1_byte();
  } while (c == 0xFF);

  if (discarded_bytes != 0) {
    fprintf(stderr, "Warning: garbage data found in JPEG file\n");
  }

  return c;
}

/*
 * Read the initial marker, which should be SOI.
 * For a JFIF file, the first two bytes of the file should be literally
 * 0xFF M_SOI.  To be more general, we could use next_marker, but if the
 * input file weren't actually JPEG at all, next_marker might read the whole
 * file and then return a misleading error message...
 */

static int
first_marker (void)
{
  int c1, c2;

  c1 = NEXTBYTE();
  c2 = NEXTBYTE();
  if (c1 != 0xFF || c2 != M_SOI)
    ERREXIT("Not a JPEG file");
  return c2;
}

/*
 * Most types of marker are followed by a variable-length parameter segment.
 * This routine skips over the parameters for any marker we don't otherwise
 * want to process.
 * Note that we MUST skip the parameter segment explicitly in order not to
 * be fooled by 0xFF bytes that might appear within the parameter segment;
 * such bytes do NOT introduce new markers.
 */

static void
skip_variable (void)
/* Skip over an unknown or uninteresting variable-length marker */
{
  unsigned int length;

  /* Get the marker parameter length count */
  length = read_2_bytes();
  /* Length includes itself, so must be at least 2 */
  if (length < 2)
    ERREXIT("Erroneous JPEG marker length");
  length -= 2;
  /* Skip over the remaining bytes */
  while (length > 0) {
    (void) read_1_byte();
    length--;
  }
}

/*
 * Process a COM marker.
 * We want to print out the marker contents as legible text;
 * we must guard against non-text junk and varying newline representations.
 */

static void
process_COM (void)
{
  unsigned int length;
  int ch;
  int lastch = 0;

  /* Get the marker parameter length count */
  length = read_2_bytes();
  /* Length includes itself, so must be at least 2 */
  if (length < 2)
    ERREXIT("Erroneous JPEG marker length");
  length -= 2;

  while (length > 0) {
    ch = read_1_byte();
    /* Emit the character in a readable form.
     * Nonprintables are converted to \nnn form,
     * while \ is converted to \\.
     * Newlines in CR, CR/LF, or LF form will be printed as one newline.
     */
    if (ch == '\r') {
      printf("\n");
    } else if (ch == '\n') {
      if (lastch != '\r')
	printf("\n");
    } else if (ch == '\\') {
      printf("\\\\");
    } else if (isprint(ch)) {
      putc(ch, stdout);
    } else {
      printf("\\%03o", ch);
    }
    lastch = ch;
    length--;
  }
  printf("\n");
}

/*
 * Process a SOFn marker.
 * This code is only needed if you want to know the image dimensions...
 */

static void
process_SOFn (int marker)
{
  unsigned int length;
  unsigned int image_height, image_width;
  int data_precision, num_components;
  const char * process;
  int ci;

  length = read_2_bytes();	/* usual parameter length count */

  data_precision = read_1_byte();
  image_height = read_2_bytes();
  image_width = read_2_bytes();
  num_components = read_1_byte();

  switch (marker) {
  case M_SOF0:	process = "Baseline";  break;
  case M_SOF1:	process = "Extended sequential";  break;
  case M_SOF2:	process = "Progressive";  break;
  case M_SOF3:	process = "Lossless";  break;
  case M_SOF5:	process = "Differential sequential";  break;
  case M_SOF6:	process = "Differential progressive";  break;
  case M_SOF7:	process = "Differential lossless";  break;
  case M_SOF9:	process = "Extended sequential, arithmetic coding";  break;
  case M_SOF10:	process = "Progressive, arithmetic coding";  break;
  case M_SOF11:	process = "Lossless, arithmetic coding";  break;
  case M_SOF13:	process = "Differential sequential, arithmetic coding";  break;
  case M_SOF14:	process = "Differential progressive, arithmetic coding"; break;
  case M_SOF15:	process = "Differential lossless, arithmetic coding";  break;
  default:	process = "Unknown";  break;
  }

  printf("JPEG image is %uw * %uh, %d color components, %d bits per sample\n",
	 image_width, image_height, num_components, data_precision);
  printf("JPEG process: %s\n", process);

  if (length != (unsigned int) (8 + num_components * 3))
    ERREXIT("Bogus SOF marker length");

  for (ci = 0; ci < num_components; ci++) {
    (void) read_1_byte();	/* Component ID code */
    (void) read_1_byte();	/* H, V sampling factors */
    (void) read_1_byte();	/* Quantization table number */
  }
}

/*
 * Parse the marker stream until SOS or EOI is seen;
 * display any COM markers.
 * While the companion program wrjpgcom will always insert COM markers before
 * SOFn, other implementations might not, so we scan to SOS before stopping.
 * If we were only interested in the image dimensions, we would stop at SOFn.
 * (Conversely, if we only cared about COM markers, there would be no need
 * for special code to handle SOFn; we could treat it like other markers.)
 */

static int
scan_JPEG_header (int verbose)
{
  int marker;

  /* Expect SOI at start of file */
  if (first_marker() != M_SOI)
    ERREXIT("Expected SOI marker first");

  /* Scan miscellaneous markers until we reach SOS. */
  for (;;) {
    marker = next_marker();
    switch (marker) {
      /* Note that marker codes 0xC4, 0xC8, 0xCC are not, and must not be,
       * treated as SOFn.  C4 in particular is actually DHT.
       */
    case M_SOF0:		/* Baseline */
    case M_SOF1:		/* Extended sequential, Huffman */
    case M_SOF2:		/* Progressive, Huffman */
    case M_SOF3:		/* Lossless, Huffman */
    case M_SOF5:		/* Differential sequential, Huffman */
    case M_SOF6:		/* Differential progressive, Huffman */
    case M_SOF7:		/* Differential lossless, Huffman */
    case M_SOF9:		/* Extended sequential, arithmetic */
    case M_SOF10:		/* Progressive, arithmetic */
    case M_SOF11:		/* Lossless, arithmetic */
    case M_SOF13:		/* Differential sequential, arithmetic */
    case M_SOF14:		/* Differential progressive, arithmetic */
    case M_SOF15:		/* Differential lossless, arithmetic */
      if (verbose)
	process_SOFn(marker);
      else
	skip_variable();
      break;

    case M_SOS:			/* stop before hitting compressed data */
      return marker;

    case M_EOI:			/* in case it's a tables-only JPEG stream */
      return marker;

    case M_COM:
      process_COM();
      break;

    case M_APP12:
      /* Some digital camera makers put useful textual information into
       * APP12 markers, so we print those out too when in -verbose mode.
       */
      if (verbose) {
	printf("APP12 contains:\n");
	process_COM();
      } else
	skip_variable();
      break;

    default:			/* Anything else just gets skipped */
      skip_variable();		/* we assume it has a parameter count... */
      break;
    }
  } /* end loop */
}

/* Command line parsing code */

static const char * progname;	/* program name for error messages */

static void
usage (void)
/* complain about bad command line */
{
  fprintf(stderr, "rdjpgcom displays any textual comments in a JPEG file.\n");

  fprintf(stderr, "Usage: %s [switches] [inputfile]\n", progname);

  fprintf(stderr, "Switches (names may be abbreviated):\n");
  fprintf(stderr, "  -verbose    Also display dimensions of JPEG image\n");

  exit(EXIT_FAILURE);
}

static int
keymatch (char * arg, const char * keyword, int minchars)
/* Case-insensitive matching of (possibly abbreviated) keyword switches. */
/* keyword is the constant keyword (must be lower case already), */
/* minchars is length of minimum legal abbreviation. */
{
  register int ca, ck;
  register int nmatched = 0;

  while ((ca = *arg++) != '\0') {
    if ((ck = *keyword++) == '\0')
      return 0;			/* arg longer than keyword, no good */
    if (isupper(ca))		/* force arg to lcase (assume ck is already) */
      ca = tolower(ca);
    if (ca != ck)
      return 0;			/* no good */
    nmatched++;			/* count matched characters */
  }
  /* reached end of argument; fail if it's too short for unique abbrev */
  if (nmatched < minchars)
    return 0;
  return 1;			/* A-OK */
}

/*
 * The main program.
 */

int
main (int argc, char **argv)
{
  int argn;
  char * arg;
  int verbose = 0;

  /* On Mac, fetch a command line. */
#ifdef USE_CCOMMAND
  argc = ccommand(&argv);
#endif

  progname = argv[0];
  if (progname == NULL || progname[0] == 0)
    progname = "rdjpgcom";	/* in case C library doesn't provide it */

  /* Parse switches, if any */
  for (argn = 1; argn < argc; argn++) {
    arg = argv[argn];
    if (arg[0] != '-')
      break;			/* not switch, must be file name */
    arg++;			/* advance over '-' */
    if (keymatch(arg, "verbose", 1)) {
      verbose++;
    } else
      usage();
  }

  /* Open the input file. */
  /* Unix style: expect zero or one file name */
  if (argn < argc-1) {
    fprintf(stderr, "%s: only one input file\n", progname);
    usage();
  }
  if (argn < argc) {
    if ((infile = fopen(argv[argn], READ_BINARY)) == NULL) {
      fprintf(stderr, "%s: can't open %s\n", progname, argv[argn]);
      exit(EXIT_FAILURE);
    }
  } else {
    /* default input file is stdin */
#ifdef USE_SETMODE		/* need to hack file mode? */
    setmode(fileno(stdin), O_BINARY);
#endif
#ifdef USE_FDOPEN		/* need to re-open in binary mode? */
    if ((infile = fdopen(fileno(stdin), READ_BINARY)) == NULL) {
      fprintf(stderr, "%s: can't open stdin\n", progname);
      exit(EXIT_FAILURE);
    }
#else
    infile = stdin;
#endif
  }

  /* Scan the JPEG headers. */
  (void) scan_JPEG_header(verbose);

  /* All done. */
  exit(EXIT_SUCCESS);
  return 0;			/* suppress no-return-value warnings */
}