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get_xbits() optimization 

Originally committed as revision 5257 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2006-03-31 20:40:22 +00:00
parent ad8812be8f
commit 6b250e4725
1 changed files with 3 additions and 9 deletions
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12
libavcodec/bitstream.h
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@ -574,21 +574,15 @@ static inline int get_bits_count(GetBitContext *s){
* @author BERO
*/
static inline int get_xbits(GetBitContext *s, int n){
register int tmp;
register int sign;
register int32_t cache;
OPEN_READER(re, s)
UPDATE_CACHE(re, s)
cache = GET_CACHE(re,s);
if ((int32_t)cache<0) { //MSB=1
tmp = NEG_USR32(cache,n);
} else {
// tmp = (-1<<n) | NEG_USR32(cache,n) + 1; mpeg12.c algo
// tmp = - (NEG_USR32(cache,n) ^ ((1 << n) - 1)); h263.c algo
tmp = - NEG_USR32(~cache,n);
}
sign=(~cache)>>31;
LAST_SKIP_BITS(re, s, n)
CLOSE_READER(re, s)
return tmp;
return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
}
static inline int get_sbits(GetBitContext *s, int n){