[x265] [PATCH 2 of 6] faster algorithm to calculate ctxSet in codeCoeffNxN()

[Deepthi Nandakumar]

On Wed, Jun 17, 2015 at 5:01 AM, Min Chen <chenm003 at 163.com> wrote:

> # HG changeset patch
> # User Min Chen <chenm003 at 163.com>
> # Date 1434495240 25200
> # Node ID 6977137391b30dbc9ed55b7bf3e35dcfb40aef9a
> # Parent  f8538b22787c8ab0d1cf65446b7e438cb02d544d
> faster algorithm to calculate ctxSet in codeCoeffNxN()
> ---
>  source/encoder/entropy.cpp |    5 ++---
>  1 files changed, 2 insertions(+), 3 deletions(-)
>
> diff -r f8538b22787c -r 6977137391b3 source/encoder/entropy.cpp
> --- a/source/encoder/entropy.cpp        Tue Jun 16 09:45:57 2015 -0700
> +++ b/source/encoder/entropy.cpp        Tue Jun 16 15:54:00 2015 -0700
> @@ -1739,9 +1739,8 @@
>              CTZ(firstNZPosInCG, subCoeffFlag);
>
>              bool signHidden = (lastNZPosInCG - firstNZPosInCG >=
> SBH_THRESHOLD);
> -            uint32_t ctxSet = ((subSet > 0) & bIsLuma) ? 2 : 0;
> -
> -            ctxSet += !(c1 & 3);
> +            const uint8_t ctxSet = (((subSet > 0) + bIsLuma) & 2) | !(c1
> & 3);
> +            X265_CHECK((((subSet > 0) & bIsLuma) ? 2 : 0) + !(c1 & 3) ==
> ctxSet, "ctxSet check failure\n");
>
> Min, this really affects readability. Are the savings from removing the
conditional operator?


>              c1 = 1;
>              uint8_t *baseCtxMod = &m_contextState[(bIsLuma ? 0 :
> NUM_ONE_FLAG_CTX_LUMA) + OFF_ONE_FLAG_CTX + 4 * ctxSet];
>
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