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move eob_reached logic into ff_lzw_decode_tail() which simplifies the code, avoids some checks in the innermost loop and also gets rid of the controversal break while hopefully retaining the last byte in a valid bytestream, invalid bytestreams still can have very significant overread

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Originally committed as revision 8517 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2007-03-25 15:43:46 +00:00
parent c59f24e657
commit 5f01beb548
1 changed files with 8 additions and 11 deletions
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19
libavcodec/lzw.c
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@ -42,7 +42,6 @@ static const uint16_t mask[17] =
};
struct LZWState {
int eob_reached;
uint8_t *pbuf, *ebuf;
int bbits;
unsigned int bbuf;
@ -74,10 +73,6 @@ static int lzw_get_code(struct LZWState * s)
while (s->bbits < s->cursize) {
if (!s->bs) {
s->bs = *s->pbuf++;
if(!s->bs) {
s->eob_reached = 1;
break;
}
}
s->bbuf |= (*s->pbuf++) << s->bbits;
s->bbits += 8;
@ -87,9 +82,6 @@ static int lzw_get_code(struct LZWState * s)
s->bbuf >>= s->cursize;
} else { // TIFF
while (s->bbits < s->cursize) {
if (s->pbuf >= s->ebuf) {
s->eob_reached = 1;
}
s->bbuf = (s->bbuf << 8) | (*s->pbuf++);
s->bbits += 8;
}
@ -107,8 +99,14 @@ uint8_t* ff_lzw_cur_ptr(LZWState *p)
void ff_lzw_decode_tail(LZWState *p)
{
struct LZWState *s = (struct LZWState *)p;
while(!s->eob_reached)
lzw_get_code(s);
if(s->mode == FF_LZW_GIF) {
while(s->pbuf < s->ebuf && s->bs>0){
s->pbuf += s->bs;
s->bs = *s->pbuf++;
}
}else
s->pbuf= s->ebuf;
}
void ff_lzw_decode_open(LZWState **p)
@ -136,7 +134,6 @@ int ff_lzw_decode_init(LZWState *p, int csize, uint8_t *buf, int buf_size, int m
if(csize < 1 || csize > LZW_MAXBITS)
return -1;
/* read buffer */
s->eob_reached = 0;
s->pbuf = buf;
s->ebuf = s->pbuf + buf_size;
s->bbuf = 0;