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- /* Copyright (C) 1996, 1997, 1998, 1999 Aladdin Enterprises. All rights reserved.
-
- This software is provided AS-IS with no warranty, either express or
- implied.
-
- This software is distributed under license and may not be copied,
- modified or distributed except as expressly authorized under the terms
- of the license contained in the file LICENSE in this distribution.
-
- For more information about licensing, please refer to
- http://www.ghostscript.com/licensing/. For information on
- commercial licensing, go to http://www.artifex.com/licensing/ or
- contact Artifex Software, Inc., 101 Lucas Valley Road #110,
- San Rafael, CA 94903, U.S.A., +1(415)492-9861.
- */
- /* $Id: spngp.c,v 1.4 2002/02/21 22:24:54 giles Exp $ */
- /* PNG pixel prediction filters */
- #include "memory_.h"
- #include "strimpl.h"
- #include "spngpx.h"
- /* ------ PNGPredictorEncode/Decode ------ */
- private_st_PNGP_state();
- /* Define values for case dispatch. */
- #define cNone 10
- #define cSub 11
- #define cUp 12
- #define cAverage 13
- #define cPaeth 14
- #define cOptimum 15
- #define cEncode -10
- #define cDecode -4
- private const byte pngp_case_needs_prev[] = {
- 0, 0, 1, 1, 1, 1
- };
- /* Set defaults */
- private void
- s_PNGP_set_defaults(stream_state * st)
- {
- stream_PNGP_state *const ss = (stream_PNGP_state *) st;
- s_PNGP_set_defaults_inline(ss);
- }
- /* Common (re)initialization. */
- private int
- s_PNGP_reinit(stream_state * st)
- {
- stream_PNGP_state *const ss = (stream_PNGP_state *) st;
- if (ss->prev_row != 0)
- memset(ss->prev_row + ss->bpp, 0, ss->row_count);
- ss->row_left = 0;
- return 0;
- }
- /* Common initialization. */
- private int
- s_pngp_init(stream_state * st, bool need_prev)
- {
- stream_PNGP_state *const ss = (stream_PNGP_state *) st;
- int bits_per_pixel = ss->Colors * ss->BitsPerComponent;
- long bits_per_row = (long)bits_per_pixel * ss->Columns;
- byte *prev_row = 0;
- #if arch_sizeof_long > arch_sizeof_int
- if (bits_per_row > max_uint * 7L)
- return ERRC; /****** WRONG ******/
- #endif
- ss->row_count = (uint) ((bits_per_row + 7) >> 3);
- ss->end_mask = (1 << (-bits_per_row & 7)) - 1;
- ss->bpp = (bits_per_pixel + 7) >> 3;
- if (need_prev) {
- prev_row = gs_alloc_bytes(st->memory, ss->bpp + ss->row_count,
- "PNGPredictor prev row");
- if (prev_row == 0)
- return ERRC; /****** WRONG ******/
- memset(prev_row, 0, ss->bpp);
- }
- ss->prev_row = prev_row;
- /* case_index is only preset for encoding */
- return s_PNGP_reinit(st);
- }
- /* Initialize PNGPredictorEncode filter. */
- private int
- s_PNGPE_init(stream_state * st)
- {
- stream_PNGP_state *const ss = (stream_PNGP_state *) st;
- return s_pngp_init(st, pngp_case_needs_prev[ss->Predictor - cNone]);
- }
- /* Initialize PNGPredictorDecode filter. */
- private int
- s_PNGPD_init(stream_state * st)
- {
- return s_pngp_init(st, true);
- }
- /* Release a PNGPredictor filter. */
- private void
- s_PNGP_release(stream_state *st)
- {
- stream_PNGP_state *const ss = (stream_PNGP_state *) st;
- if (ss->prev_row)
- gs_free_object(st->memory, ss->prev_row, "PNGPredictor prev row");
- }
- /*
- * Process a partial buffer. We pass in current and previous pointers
- * to both the current and preceding scan line. Note that dprev is
- * p - bpp for encoding, q - bpp for decoding; similarly, the 'up' row
- * is the raw data for encoding, the filtered data for decoding.
- * Note also that the case_index cannot be cOptimum.
- */
- private int
- paeth_predictor(int a, int b, int c)
- {
- /* The definitions of ac and bc are correct, not a typo. */
- int ac = b - c, bc = a - c, abcc = ac + bc;
- int pa = (ac < 0 ? -ac : ac), pb = (bc < 0 ? -bc : bc),
- pc = (abcc < 0 ? -abcc : abcc);
- return (pa <= pb && pa <= pc ? a : pb <= pc ? b : c);
- }
- private void
- s_pngp_process(stream_state * st, stream_cursor_write * pw,
- const byte * dprev, stream_cursor_read * pr,
- const byte * upprev, const byte * up, uint count)
- {
- stream_PNGP_state *const ss = (stream_PNGP_state *) st;
- byte *q = pw->ptr + 1;
- const byte *p = pr->ptr + 1;
- pr->ptr += count;
- pw->ptr += count;
- ss->row_left -= count;
- switch (ss->case_index) {
- case cEncode + cNone:
- case cDecode + cNone:
- memcpy(q, p, count);
- break;
- case cEncode + cSub:
- for (; count; ++q, ++dprev, ++p, --count)
- *q = (byte) (*p - *dprev);
- break;
- case cDecode + cSub:
- for (; count; ++q, ++dprev, ++p, --count)
- *q = (byte) (*p + *dprev);
- break;
- case cEncode + cUp:
- for (; count; ++q, ++up, ++p, --count)
- *q = (byte) (*p - *up);
- break;
- case cDecode + cUp:
- for (; count; ++q, ++up, ++p, --count)
- *q = (byte) (*p + *up);
- break;
- case cEncode + cAverage:
- for (; count; ++q, ++dprev, ++up, ++p, --count)
- *q = (byte) (*p - arith_rshift_1((int)*dprev + (int)*up));
- break;
- case cDecode + cAverage:
- for (; count; ++q, ++dprev, ++up, ++p, --count)
- *q = (byte) (*p + arith_rshift_1((int)*dprev + (int)*up));
- break;
- case cEncode + cPaeth:
- for (; count; ++q, ++dprev, ++up, ++upprev, ++p, --count)
- *q = (byte) (*p - paeth_predictor(*dprev, *up, *upprev));
- break;
- case cDecode + cPaeth:
- for (; count; ++q, ++dprev, ++up, ++upprev, ++p, --count)
- *q = (byte) (*p + paeth_predictor(*dprev, *up, *upprev));
- break;
- }
- }
- /* Calculate the number of bytes for the next processing step, */
- /* the min of (input data, output data, remaining row length). */
- private uint
- s_pngp_count(const stream_state * st_const, const stream_cursor_read * pr,
- const stream_cursor_write * pw)
- {
- const stream_PNGP_state *const ss_const =
- (const stream_PNGP_state *)st_const;
- uint rcount = pr->limit - pr->ptr;
- uint wcount = pw->limit - pw->ptr;
- uint row_left = ss_const->row_left;
- if (rcount < row_left)
- row_left = rcount;
- if (wcount < row_left)
- row_left = wcount;
- return row_left;
- }
- /*
- * Encode a buffer. Let N = ss->row_count, P = N - ss->row_left,
- * and B = ss->bpp. Consider that bytes [-B .. -1] of every row are zero.
- * Then:
- * prev_row[0 .. P - 1] contain bytes -B .. P - B - 1
- * of the current input row.
- * ss->prev[0 .. B - 1] contain bytes P - B .. P - 1
- * of the current input row.
- * prev_row[P .. N + B - 1] contain bytes P - B .. N - 1
- * of the previous input row.
- */
- private int
- optimum_predictor(const stream_state * st, const stream_cursor_read * pr)
- {
- return cSub;
- }
- private int
- s_PNGPE_process(stream_state * st, stream_cursor_read * pr,
- stream_cursor_write * pw, bool last)
- {
- stream_PNGP_state *const ss = (stream_PNGP_state *) st;
- int bpp = ss->bpp;
- int status = 0;
- while (pr->ptr < pr->limit) {
- uint count;
- if (ss->row_left == 0) {
- /* Beginning of row, write algorithm byte. */
- int predictor;
- if (pw->ptr >= pw->limit) {
- status = 1;
- break;
- }
- predictor =
- (ss->Predictor == cOptimum ?
- optimum_predictor(st, pr) :
- ss->Predictor);
- *++(pw->ptr) = (byte) predictor - cNone;
- ss->case_index = predictor + cEncode;
- ss->row_left = ss->row_count;
- memset(ss->prev, 0, bpp);
- continue;
- }
- count = s_pngp_count(st, pr, pw);
- if (count == 0) {
- /* We know we have input, so output must be full. */
- status = 1;
- break;
- } {
- byte *up = ss->prev_row + bpp + ss->row_count - ss->row_left;
- uint n = min(count, bpp);
- /* Process bytes whose predecessors are in prev. */
- s_pngp_process(st, pw, ss->prev, pr, up - bpp, up, n);
- if (ss->prev_row)
- memcpy(up - bpp, ss->prev, n);
- if (ss->row_left == 0)
- continue;
- if (n < bpp) {
- /*
- * We didn't have both enough input data and enough output
- * space to use up all of prev. Shift more data into prev
- * and exit.
- */
- int prev_left = bpp - n;
- memmove(ss->prev, ss->prev + n, prev_left);
- memcpy(ss->prev + prev_left, pr->ptr - (n - 1), n);
- if (pw->ptr >= pw->limit && pr->ptr < pr->limit)
- status = 1;
- break;
- }
- /* Process bytes whose predecessors are in the input. */
- /* We know we have at least bpp input and output bytes, */
- /* and that n = bpp. */
- count -= bpp;
- s_pngp_process(st, pw, pr->ptr - (bpp - 1), pr,
- up, up + bpp, count);
- memcpy(ss->prev, pr->ptr - (bpp - 1), bpp);
- if (ss->prev_row) {
- memcpy(up, pr->ptr - (bpp + count - 1), count);
- if (ss->row_left == 0)
- memcpy(up + count, ss->prev, bpp);
- }
- }
- }
- return status;
- }
- /*
- * Decode a buffer. Let N = ss->row_count, P = N - ss->row_left,
- * and B = ss->bpp. Consider that bytes [-B .. -1] of every row are zero.
- * Then:
- * prev_row[0 .. P - 1] contain bytes -B .. P - B - 1
- * of the current output row.
- * ss->prev[0 .. B - 1] contain bytes P - B .. P - 1
- * of the current output row.
- * prev_row[P .. N + B - 1] contain bytes P - B .. N - 1
- * of the previous output row.
- */
- private int
- s_PNGPD_process(stream_state * st, stream_cursor_read * pr,
- stream_cursor_write * pw, bool last)
- {
- stream_PNGP_state *const ss = (stream_PNGP_state *) st;
- int bpp = ss->bpp;
- int status = 0;
- while (pr->ptr < pr->limit) {
- uint count;
- if (ss->row_left == 0) {
- /* Beginning of row, read algorithm byte. */
- int predictor = pr->ptr[1];
- if (predictor >= cOptimum - cNone) {
- status = ERRC;
- break;
- }
- pr->ptr++;
- ss->case_index = predictor + cNone + cDecode;
- ss->row_left = ss->row_count;
- memset(ss->prev, 0, bpp);
- continue;
- }
- count = s_pngp_count(st, pr, pw);
- if (count == 0) {
- /* We know we have input, so output must be full. */
- status = 1;
- break;
- } {
- byte *up = ss->prev_row + bpp + ss->row_count - ss->row_left;
- uint n = min(count, bpp);
- /* Process bytes whose predecessors are in prev. */
- s_pngp_process(st, pw, ss->prev, pr, up - bpp, up, n);
- if (ss->prev_row)
- memcpy(up - bpp, ss->prev, n);
- if (ss->row_left == 0)
- continue;
- if (n < bpp) {
- /*
- * We didn't have both enough input data and enough output
- * space to use up all of prev. Shift more data into prev
- * and exit.
- */
- int prev_left = bpp - n;
- memmove(ss->prev, ss->prev + n, prev_left);
- memcpy(ss->prev + prev_left, pw->ptr - (n - 1), n);
- if (pw->ptr >= pw->limit && pr->ptr < pr->limit)
- status = 1;
- break;
- }
- /* Process bytes whose predecessors are in the output. */
- /* We know we have at least bpp input and output bytes, */
- /* and that n = bpp. */
- count -= bpp;
- s_pngp_process(st, pw, pw->ptr - (bpp - 1), pr,
- up, up + bpp, count);
- memcpy(ss->prev, pw->ptr - (bpp - 1), bpp);
- if (ss->prev_row) {
- memcpy(up, pw->ptr - (bpp + count - 1), count);
- if (ss->row_left == 0)
- memcpy(up + count, ss->prev, bpp);
- }
- }
- }
- return status;
- }
- /* Stream templates */
- const stream_template s_PNGPE_template = {
- &st_PNGP_state, s_PNGPE_init, s_PNGPE_process, 1, 1, s_PNGP_release,
- s_PNGP_set_defaults, s_PNGP_reinit
- };
- const stream_template s_PNGPD_template = {
- &st_PNGP_state, s_PNGPD_init, s_PNGPD_process, 1, 1, s_PNGP_release,
- s_PNGP_set_defaults, s_PNGP_reinit
- };
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