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CMOV-ify vp56 arithcoder

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This incantation causes gcc 4.3 to generate cmov on x86, a vastly better option
than a completely unpredictable branch.
Hopefully this carries over to newer versions and other CPUs with conditionals.
~5 cycles saved per call on a Core i7.

Originally committed as revision 23921 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Jason Garrett-Glaser 2010-06-30 23:18:47 +00:00
parent 2e6ed48d6e
commit 36d6b545a1
1 changed files with 2 additions and 6 deletions
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8
libavcodec/vp56.h
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@ -199,12 +199,8 @@ static inline int vp56_rac_get_prob(VP56RangeCoder *c, uint8_t prob)
int bit = c->code_word >= low_shift;
int shift;
if (bit) {
c->high -= low;
c->code_word -= low_shift;
} else {
c->high = low;
}
c->high = bit ? c->high - low : low;
c->code_word = bit ? c->code_word - low_shift : c->code_word;
/* normalize */
shift = ff_h264_norm_shift[c->high] - 1;