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Optimize vp56 arithmetic decoder

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Negate "bits" to eliminate a negate in cache refilling.

Originally committed as revision 23920 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Jason Garrett-Glaser 2010-06-30 23:15:25 +00:00
parent b0a18c2f0a
commit 2e6ed48d6e
1 changed files with 9 additions and 8 deletions
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17
libavcodec/vp56.h
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@ -48,7 +48,8 @@ typedef int (*VP56ParseHeader)(VP56Context *s, const uint8_t *buf,
typedef struct { typedef struct {
int high; int high;
int bits; int bits; /* Stored negated (i.e. negative "bits" is a positive number of bits left)
* in order to eliminate a negate in cache refilling */
const uint8_t *buffer; const uint8_t *buffer;
const uint8_t *end; const uint8_t *end;
unsigned long code_word; unsigned long code_word;
@ -185,7 +186,7 @@ static inline void vp56_init_range_decoder(VP56RangeCoder *c,
const uint8_t *buf, int buf_size) const uint8_t *buf, int buf_size)
{ {
c->high = 255; c->high = 255;
c->bits = 8; c->bits = -8;
c->buffer = buf; c->buffer = buf;
c->end = buf + buf_size; c->end = buf + buf_size;
c->code_word = bytestream_get_be16(&c->buffer); c->code_word = bytestream_get_be16(&c->buffer);
@ -209,10 +210,10 @@ static inline int vp56_rac_get_prob(VP56RangeCoder *c, uint8_t prob)
shift = ff_h264_norm_shift[c->high] - 1; shift = ff_h264_norm_shift[c->high] - 1;
c->high <<= shift; c->high <<= shift;
c->code_word <<= shift; c->code_word <<= shift;
c->bits -= shift; c->bits += shift;
if(c->bits <= 0 && c->buffer < c->end) { if(c->bits >= 0 && c->buffer < c->end) {
c->code_word |= *c->buffer++ << -c->bits; c->code_word |= *c->buffer++ << c->bits;
c->bits += 8; c->bits -= 8;
} }
return bit; return bit;
} }
@ -232,8 +233,8 @@ static inline int vp56_rac_get(VP56RangeCoder *c)
/* normalize */ /* normalize */
c->code_word <<= 1; c->code_word <<= 1;
if (--c->bits == 0 && c->buffer < c->end) { if (++c->bits == 0 && c->buffer < c->end) {
c->bits = 8; c->bits = -8;
c->code_word |= *c->buffer++; c->code_word |= *c->buffer++;
} }
return bit; return bit;