From: Matthew Fearnley <[email protected]>
If *xored is 0, then histogram[0]==bw*bh and histogram[1..255]==0.
Because histogram[0] is skipped over for the entropy calculation, the
return value is always 0 when *xored==0, so we don't need to waste time
calculating it.
This addition both clarifies the behaviour of the code and improves
the speed when the block matches.
---
libavcodec/zmbvenc.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/libavcodec/zmbvenc.c b/libavcodec/zmbvenc.c
index 4d9147657d..2f041dae32 100644
--- a/libavcodec/zmbvenc.c
+++ b/libavcodec/zmbvenc.c
@@ -71,6 +71,7 @@ static inline int block_cmp(ZmbvEncContext *c, uint8_t *src,
int stride,
int i, j;
uint8_t histogram[256] = {0};
+ /* build frequency histogram of byte values for src[] ^ src2[] */
*xored = 0;
for(j = 0; j < bh; j++){
for(i = 0; i < bw; i++){
@@ -82,6 +83,10 @@ static inline int block_cmp(ZmbvEncContext *c, uint8_t *src,
int stride,
src2 += stride2;
}
+ /* early out if src and src2 are equal */
+ if (!*xored) return 0;
+
+ /* sum the entropy of the non-zero values */
for(i = 1; i < 256; i++)
sum += c->score_tab[histogram[i]];
--
2.17.1
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