Commit 2e6ed48d authored by Jason Garrett-Glaser's avatar Jason Garrett-Glaser
Browse files

Optimize vp56 arithmetic decoder

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

Originally committed as revision 23920 to svn://svn.ffmpeg.org/ffmpeg/trunk
parent b0a18c2f
......@@ -48,7 +48,8 @@ typedef int (*VP56ParseHeader)(VP56Context *s, const uint8_t *buf,
typedef struct {
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 *end;
unsigned long code_word;
......@@ -185,7 +186,7 @@ static inline void vp56_init_range_decoder(VP56RangeCoder *c,
const uint8_t *buf, int buf_size)
{
c->high = 255;
c->bits = 8;
c->bits = -8;
c->buffer = buf;
c->end = buf + buf_size;
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;
c->high <<= shift;
c->code_word <<= shift;
c->bits -= shift;
if(c->bits <= 0 && c->buffer < c->end) {
c->code_word |= *c->buffer++ << -c->bits;
c->bits += 8;
c->bits += shift;
if(c->bits >= 0 && c->buffer < c->end) {
c->code_word |= *c->buffer++ << c->bits;
c->bits -= 8;
}
return bit;
}
......@@ -232,8 +233,8 @@ static inline int vp56_rac_get(VP56RangeCoder *c)
/* normalize */
c->code_word <<= 1;
if (--c->bits == 0 && c->buffer < c->end) {
c->bits = 8;
if (++c->bits == 0 && c->buffer < c->end) {
c->bits = -8;
c->code_word |= *c->buffer++;
}
return bit;
......
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment