ons 2018-12-19 klockan 22:00 +0000 skrev matthew.w.fearn...@gmail.com:
> > From: Matthew Fearnley <matthew.w.fearn...@gmail.com>
>
> 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;
I have a feeling this could be sped up further by just doing *xored =
histogram[0] == ZMBV_BLOCK*ZMBV_BLOCK after the loops, if [PATCH 3/4]
is applied before this. Computing both histogram and xored in the loop
seems pointless.
Beyond that this looks good
/Tomas
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