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find_start_code() optimization (about 2x faster now) this may improve decoding speed with multiple threads

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Originally committed as revision 2862 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2004-03-09 15:23:14 +00:00
parent ba30abcb0d
commit c7516a000c
1 changed files with 17 additions and 14 deletions
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31
libavcodec/mpeg12.c
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@ -1770,24 +1770,27 @@ static int mpeg_decode_init(AVCodecContext *avctx)
state. Return -1 if no start code found */ state. Return -1 if no start code found */
static int find_start_code(const uint8_t **pbuf_ptr, const uint8_t *buf_end) static int find_start_code(const uint8_t **pbuf_ptr, const uint8_t *buf_end)
{ {
const uint8_t *buf_ptr; const uint8_t *buf_ptr= *pbuf_ptr;
unsigned int state=0xFFFFFFFF, v;
int val; buf_ptr++; //gurantees that -1 is within the array
buf_end -= 2; // gurantees that +2 is within the array
buf_ptr = *pbuf_ptr;
while (buf_ptr < buf_end) { while (buf_ptr < buf_end) {
v = *buf_ptr++; if(*buf_ptr==0){
if (state == 0x000001) { while(buf_ptr < buf_end && buf_ptr[1]==0)
state = ((state << 8) | v) & 0xffffff; buf_ptr++;
val = state;
goto found; if(buf_ptr[-1] == 0 && buf_ptr[1] == 1){
*pbuf_ptr = buf_ptr+3;
return buf_ptr[2] + 0x100;
}
} }
state = ((state << 8) | v) & 0xffffff; buf_ptr += 2;
} }
val = -1; buf_end += 2; //undo the hack above
found:
*pbuf_ptr = buf_ptr; *pbuf_ptr = buf_end;
return val; return -1;
} }
static int mpeg1_decode_picture(AVCodecContext *avctx, static int mpeg1_decode_picture(AVCodecContext *avctx,