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/*
* The Python Imaging Library.
* $Id$
*
* a fast, suspendable GIF decoder
*
* history:
* 95-09-03 fl Created
* 95-09-05 fl Fixed sign problem on 16-bit platforms
* 95-09-13 fl Added some storage shortcuts
* 96-03-28 fl Revised API, integrated with PIL
* 96-12-10 fl Added interlace support
* 96-12-16 fl Fixed premature termination bug introduced by last fix
* 97-01-05 fl Don't mess up on bogus configuration
* 97-01-17 fl Don't mess up on very small, interlaced files
* 99-02-07 fl Minor speedups
*
* Copyright (c) Secret Labs AB 1997-99.
* Copyright (c) Fredrik Lundh 1995-97.
*
* See the README file for information on usage and redistribution.
*/
#include "Imaging.h"
#include <stdio.h>
#include <memory.h> /* memcpy() */
#include "Gif.h"
#define NEWLINE(state, context) \
{ \
state->x = 0; \
state->y += context->step; \
while (state->y >= state->ysize) switch (context->interlace) { \
case 1: \
context->repeat = state->y = 4; \
context->interlace = 2; \
break; \
case 2: \
context->step = 4; \
context->repeat = state->y = 2; \
context->interlace = 3; \
break; \
case 3: \
context->step = 2; \
context->repeat = state->y = 1; \
context->interlace = 0; \
break; \
default: \
return -1; \
} \
if (state->y < state->ysize) { \
out = im->image8[state->y + state->yoff] + state->xoff; \
} \
}
int
ImagingGifDecode(Imaging im, ImagingCodecState state, UINT8 *buffer, Py_ssize_t bytes) {
UINT8 *p;
UINT8 *out;
int c, i;
int thiscode;
GIFDECODERSTATE *context = (GIFDECODERSTATE *)state->context;
UINT8 *ptr = buffer;
if (!state->state) {
/* Initialise state */
if (context->bits < 0 || context->bits > 12) {
state->errcode = IMAGING_CODEC_CONFIG;
return -1;
}
/* Clear code */
context->clear = 1 << context->bits;
/* End code */
context->end = context->clear + 1;
/* Interlace */
if (context->interlace) {
context->interlace = 1;
context->step = context->repeat = 8;
} else {
context->step = 1;
}
state->state = 1;
}
out = im->image8[state->y + state->yoff] + state->xoff + state->x;
for (;;) {
if (state->state == 1) {
/* First free entry in table */
context->next = context->clear + 2;
/* Initial code size */
context->codesize = context->bits + 1;
context->codemask = (1 << context->codesize) - 1;
/* Buffer pointer. We fill the buffer from right, which
allows us to return all of it in one operation. */
context->bufferindex = GIFBUFFER;
state->state = 2;
}
if (context->bufferindex < GIFBUFFER) {
/* Return whole buffer in one chunk */
i = GIFBUFFER - context->bufferindex;
p = &context->buffer[context->bufferindex];
context->bufferindex = GIFBUFFER;
} else {
/* Get current symbol */
while (context->bitcount < context->codesize) {
if (context->blocksize > 0) {
/* Read next byte */
c = *ptr++;
bytes--;
context->blocksize--;
/* New bits are shifted in from the left. */
context->bitbuffer |= (INT32)c << context->bitcount;
context->bitcount += 8;
} else {
/* New GIF block */
/* We don't start decoding unless we have a full block */
if (bytes < 1) {
return ptr - buffer;
}
c = *ptr;
if (bytes < c + 1) {
return ptr - buffer;
}
context->blocksize = c;
ptr++;
bytes--;
}
}
/* Extract current symbol from bit buffer. */
c = (int)context->bitbuffer & context->codemask;
/* Adjust buffer */
context->bitbuffer >>= context->codesize;
context->bitcount -= context->codesize;
/* If c is less than "clear", it's a data byte. Otherwise,
it's either clear/end or a code symbol which should be
expanded. */
if (c == context->clear) {
if (state->state != 2) {
state->state = 1;
}
continue;
}
if (c == context->end) {
break;
}
i = 1;
p = &context->lastdata;
if (state->state == 2) {
/* First valid symbol after clear; use as is */
if (c > context->clear) {
state->errcode = IMAGING_CODEC_BROKEN;
return -1;
}
context->lastdata = context->lastcode = c;
state->state = 3;
} else {
thiscode = c;
if (c > context->next) {
state->errcode = IMAGING_CODEC_BROKEN;
return -1;
}
if (c == context->next) {
/* c == next is allowed. not sure why. */
if (context->bufferindex <= 0) {
state->errcode = IMAGING_CODEC_BROKEN;
return -1;
}
context->buffer[--context->bufferindex] = context->lastdata;
c = context->lastcode;
}
while (c >= context->clear) {
/* Copy data string to buffer (beginning from right) */
if (context->bufferindex <= 0 || c >= GIFTABLE) {
state->errcode = IMAGING_CODEC_BROKEN;
return -1;
}
context->buffer[--context->bufferindex] = context->data[c];
c = context->link[c];
}
context->lastdata = c;
if (context->next < GIFTABLE) {
/* We'll only add this symbol if we have room
for it (take the advice, Netscape!) */
context->data[context->next] = c;
context->link[context->next] = context->lastcode;
if (context->next == context->codemask &&
context->codesize < GIFBITS) {
/* Expand code size */
context->codesize++;
context->codemask = (1 << context->codesize) - 1;
}
context->next++;
}
context->lastcode = thiscode;
}
}
/* Copy the bytes into the image */
if (state->y >= state->ysize) {
state->errcode = IMAGING_CODEC_OVERRUN;
return -1;
}
/* To squeeze some extra pixels out of this loop, we test for
some common cases and handle them separately. */
/* This cannot be used if there is transparency */
if (context->transparency == -1) {
if (i == 1) {
if (state->x < state->xsize - 1) {
/* Single pixel, not at the end of the line. */
*out++ = p[0];
state->x++;
continue;
}
} else if (state->x + i <= state->xsize) {
/* This string fits into current line. */
memcpy(out, p, i);
out += i;
state->x += i;
if (state->x == state->xsize) {
NEWLINE(state, context);
}
continue;
}
}
/* No shortcut, copy pixel by pixel */
for (c = 0; c < i; c++) {
if (p[c] != context->transparency) {
*out = p[c];
}
out++;
if (++state->x >= state->xsize) {
NEWLINE(state, context);
}
}
}
return ptr - buffer;
}
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