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Split renorm of vp56 arith decoder to its own function

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Originally committed as revision 24466 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
David Conrad 2010-07-23 21:46:08 +00:00
parent 24675b8093
commit b3d755ec8b
1 changed files with 20 additions and 16 deletions
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36
libavcodec/vp56.h
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@ -191,25 +191,11 @@ static inline void vp56_init_range_decoder(VP56RangeCoder *c,
c->code_word = bytestream_get_be16(&c->buffer); c->code_word = bytestream_get_be16(&c->buffer);
} }
static inline int vp56_rac_get_prob(VP56RangeCoder *c, uint8_t prob) static av_always_inline void vp56_rac_renorm(VP56RangeCoder *c, unsigned int code_word)
{ {
/* Don't put c->high in a local variable; if we do that, gcc gets int shift = ff_h264_norm_shift[c->high] - 1;
* the stupids and turns the code below into a branch again. */
int bits = c->bits; int bits = c->bits;
unsigned int code_word = c->code_word;
unsigned int low = 1 + (((c->high - 1) * prob) >> 8);
unsigned int low_shift = low << 8;
int bit = code_word >= low_shift;
int shift;
/* Incantation to convince GCC to turn these into conditional moves
* instead of branches -- faster, as this branch is basically
* unpredictable. */
c->high = bit ? c->high - low : low;
code_word = bit ? code_word - low_shift : code_word;
/* normalize */
shift = ff_h264_norm_shift[c->high] - 1;
c->high <<= shift; c->high <<= shift;
code_word <<= shift; code_word <<= shift;
bits += shift; bits += shift;
@ -219,6 +205,24 @@ static inline int vp56_rac_get_prob(VP56RangeCoder *c, uint8_t prob)
} }
c->bits = bits; c->bits = bits;
c->code_word = code_word; c->code_word = code_word;
}
static inline int vp56_rac_get_prob(VP56RangeCoder *c, uint8_t prob)
{
/* Don't put c->high in a local variable; if we do that, gcc gets
* the stupids and turns the code below into a branch again. */
unsigned int code_word = c->code_word;
unsigned int low = 1 + (((c->high - 1) * prob) >> 8);
unsigned int low_shift = low << 8;
int bit = code_word >= low_shift;
/* Incantation to convince GCC to turn these into conditional moves
* instead of branches -- faster, as this branch is basically
* unpredictable. */
c->high = bit ? c->high - low : low;
code_word = bit ? code_word - low_shift : code_word;
vp56_rac_renorm(c, code_word);
return bit; return bit;
} }