/*
 * jquant1.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1991-1996, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2009, 2015, D. R. Commander.
 * For conditions of distribution and use, see the accompanying README.ijg
 * 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 UINT8 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.
 */

#if BITS_IN_JSAMPLE == 8
typedef INT16 FSERROR;          /* 16 bits should be enough */
typedef int LOCFSERROR;         /* use 'int' for calculation temps */
#else
typedef JLONG FSERROR;          /* may need more than 16 bits */
typedef JLONG LOCFSERROR;       /* be sure calculation temps are big enough */
#endif

typedef FSERROR *FSERRPTR;  /* pointer to error array */


/* 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.
	 */
	boolean 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 */
	boolean 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;
	boolean changed;
	long temp;
	int RGB_order[3] = {RGB_GREEN, RGB_RED, RGB_BLUE};
	RGB_order[0] = rgb_green[cinfo->out_color_space];
	RGB_order[1] = rgb_red[cinfo->out_color_space];
	RGB_order[2] = rgb_blue[cinfo->out_color_space];

	/* 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 cinfo, int ci, 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) (((JLONG) j * MAXJSAMPLE + maxj / 2) / maxj);
}


LOCAL(int)
largest_input_value(j_decompress_ptr cinfo, int ci, 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) (((JLONG) (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;
	JLONG 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 * ((JLONG) (ncolors - 1));
	for (j = 0; j < ODITHER_SIZE; j++) {
		for (k = 0; k < ODITHER_SIZE; k++) {
			num = ((JLONG) (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 *) 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 *) 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, boolean is_pre_scan) {
	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 *) 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 cinfo) {
	/* 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 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 */
