/* Perform Lempel-Ziv-Welch decoding */
static int do_lzw(gif_struct *gs, const PRUint8 *q)
{
int code;
int incode;
const PRUint8 *ch;
/* Copy all the decoder state variables into locals so the compiler
* won't worry about them being aliased. The locals will be homed
* back into the GIF decoder structure when we exit.
*/
int avail = gs->avail;
int bits = gs->bits;
int codesize = gs->codesize;
int codemask = gs->codemask;
int count = gs->count;
int oldcode = gs->oldcode;
int clear_code = gs->clear_code;
PRUint8 firstchar = gs->firstchar;
PRInt32 datum = gs->datum;
PRUint16 *prefix = gs->prefix;
PRUint8 *stackp = gs->stackp;
PRUint8 *suffix = gs->suffix;
PRUint8 *stack = gs->stack;
PRUint8 *rowp = gs->rowp;
PRUint8 *rowend = gs->rowend;
PRUintn rows_remaining = gs->rows_remaining;
if (rowp == rowend)
return 0;
#define OUTPUT_ROW(gs) \
PR_BEGIN_MACRO \
output_row(gs); \
rows_remaining--; \
rowp = gs->rowp; \
if (!rows_remaining) \
goto END; \
PR_END_MACRO
for (ch = q; count-- > 0; ch++)
{
/* Feed the next byte into the decoder's 32-bit input buffer. */
datum += ((int32) *ch) << bits;
bits += 8;
/* Check for underflow of decoder's 32-bit input buffer. */
while (bits >= codesize)
{
/* Get the leading variable-length symbol from the data stream */
code = datum & codemask;
datum >>= codesize;
bits -= codesize;
/* Reset the dictionary to its original state, if requested */
if (code == clear_code) {
codesize = gs->datasize + 1;
codemask = (1 << codesize) - 1;
avail = clear_code + 2;
oldcode = -1;
continue;
}
/* Check for explicit end-of-stream code */
if (code == (clear_code + 1)) {
/* end-of-stream should only appear after all image data */
if (rows_remaining != 0)
return -1;
return 0;
}
if (oldcode == -1) {
*rowp++ = suffix[code];
if (rowp == rowend)
OUTPUT_ROW(gs);
firstchar = oldcode = code;
continue;
}
incode = code;
if (code >= avail) {
*stackp++ = firstchar;
code = oldcode;
if (stackp == stack + MAX_BITS)
return -1;
}
while (code >= clear_code)
{
if (code == prefix[code])
return -1;
*stackp++ = suffix[code];
code = prefix[code];
if (stackp == stack + MAX_BITS || code >= MAX_BITS)
return -1;
}
*stackp++ = firstchar = suffix[code];
/* Define a new codeword in the dictionary. */
if (avail < 4096) {
prefix[avail] = oldcode;
suffix[avail] = firstchar;
avail++;
/* If we've used up all the codewords of a given length
* increase the length of codewords by one bit, but don't
* exceed the specified maximum codeword size of 12 bits.
*/
if (((avail & codemask) == 0) && (avail < 4096)) {
codesize++;
codemask += avail;
}
}
oldcode = incode;
/* Copy the decoded data out to the scanline buffer. */
do {
*rowp++ = *--stackp;
if (rowp == rowend) {
OUTPUT_ROW(gs);
}
} while (stackp > stack);
}
}
END:
/* Home the local copies of the GIF decoder state variables */
gs->avail = avail;
gs->bits = bits;
gs->codesize = codesize;
gs->codemask = codemask;
gs->count = count;
gs->oldcode = oldcode;
gs->firstchar = firstchar;
gs->datum = datum;
gs->stackp = stackp;
gs->rowp = rowp;
gs->rows_remaining = rows_remaining;
return 0;
}
/* Perform Lempel-Ziv-Welch decoding */
bool
nsGIFDecoder2::DoLzw(const uint8_t *q)
{
if (!mGIFStruct.rows_remaining)
return true;
/* Copy all the decoder state variables into locals so the compiler
* won't worry about them being aliased. The locals will be homed
* back into the GIF decoder structure when we exit.
*/
int avail = mGIFStruct.avail;
int bits = mGIFStruct.bits;
int codesize = mGIFStruct.codesize;
int codemask = mGIFStruct.codemask;
int count = mGIFStruct.count;
int oldcode = mGIFStruct.oldcode;
const int clear_code = ClearCode();
uint8_t firstchar = mGIFStruct.firstchar;
int32_t datum = mGIFStruct.datum;
uint16_t *prefix = mGIFStruct.prefix;
uint8_t *stackp = mGIFStruct.stackp;
uint8_t *suffix = mGIFStruct.suffix;
uint8_t *stack = mGIFStruct.stack;
uint8_t *rowp = mGIFStruct.rowp;
uint32_t bpr = mGIFStruct.width;
if (!mGIFStruct.images_decoded)
bpr *= sizeof(uint32_t);
uint8_t *rowend = mImageData + (bpr * mGIFStruct.irow) + mGIFStruct.width;
#define OUTPUT_ROW() \
PR_BEGIN_MACRO \
if (!OutputRow()) \
goto END; \
rowp = mImageData + mGIFStruct.irow * bpr; \
rowend = rowp + mGIFStruct.width; \
PR_END_MACRO
for (const uint8_t* ch = q; count-- > 0; ch++)
{
/* Feed the next byte into the decoder's 32-bit input buffer. */
datum += ((int32_t) *ch) << bits;
bits += 8;
/* Check for underflow of decoder's 32-bit input buffer. */
while (bits >= codesize)
{
/* Get the leading variable-length symbol from the data stream */
int code = datum & codemask;
datum >>= codesize;
bits -= codesize;
/* Reset the dictionary to its original state, if requested */
if (code == clear_code) {
codesize = mGIFStruct.datasize + 1;
codemask = (1 << codesize) - 1;
avail = clear_code + 2;
oldcode = -1;
continue;
}
/* Check for explicit end-of-stream code */
if (code == (clear_code + 1)) {
/* end-of-stream should only appear after all image data */
return (mGIFStruct.rows_remaining == 0);
}
if (oldcode == -1) {
if (code >= MAX_BITS)
return false;
*rowp++ = suffix[code] & mColorMask; // ensure index is within colormap
if (rowp == rowend)
OUTPUT_ROW();
firstchar = oldcode = code;
continue;
}
int incode = code;
if (code >= avail) {
*stackp++ = firstchar;
code = oldcode;
if (stackp >= stack + MAX_BITS)
return false;
}
while (code >= clear_code)
{
if ((code >= MAX_BITS) || (code == prefix[code]))
return false;
*stackp++ = suffix[code];
code = prefix[code];
if (stackp == stack + MAX_BITS)
return false;
}
*stackp++ = firstchar = suffix[code];
/* Define a new codeword in the dictionary. */
if (avail < 4096) {
prefix[avail] = oldcode;
suffix[avail] = firstchar;
avail++;
/* If we've used up all the codewords of a given length
* increase the length of codewords by one bit, but don't
* exceed the specified maximum codeword size of 12 bits.
*/
if (((avail & codemask) == 0) && (avail < 4096)) {
codesize++;
codemask += avail;
}
}
oldcode = incode;
/* Copy the decoded data out to the scanline buffer. */
do {
*rowp++ = *--stackp & mColorMask; // ensure index is within colormap
if (rowp == rowend)
OUTPUT_ROW();
} while (stackp > stack);
}
}
END:
/* Home the local copies of the GIF decoder state variables */
mGIFStruct.avail = avail;
mGIFStruct.bits = bits;
mGIFStruct.codesize = codesize;
mGIFStruct.codemask = codemask;
mGIFStruct.count = count;
mGIFStruct.oldcode = oldcode;
mGIFStruct.firstchar = firstchar;
mGIFStruct.datum = datum;
mGIFStruct.stackp = stackp;
mGIFStruct.rowp = rowp;
return true;
}
