[x265] [PATCH] entropy: improve exp-Golomb code by CLZ

[chen]

At 2015-11-10 16:47:42,"Ximing Cheng" <chengximing1989 at foxmail.com> wrote:
># HG changeset patch
># User Ximing Cheng <ximingcheng at tencent.com>
># Date 1447145224 -28800
>#      Tue Nov 10 16:47:04 2015 +0800
># Node ID 73414b349436eb0b4793021e4d130b1ac48177b5
># Parent  f11b17b4656a85a15dc82fd04485fbf920848e4d
>entropy: improve exp-Golomb code by CLZ
>
>diff -r f11b17b4656a -r 73414b349436 source/common/bitstream.cpp
>--- a/source/common/bitstream.cpp	Fri Nov 06 16:04:23 2015 +0800
>+++ b/source/common/bitstream.cpp	Tue Nov 10 16:47:04 2015 +0800
>@@ -1,5 +1,6 @@
> #include "common.h"
> #include "bitstream.h"
>+#include "threading.h"
> 
> using namespace X265_NS;
> 
>@@ -112,16 +113,13 @@
> 
> void SyntaxElementWriter::writeUvlc(uint32_t code)
> {
>-    uint32_t length = 1;
>-    uint32_t temp = ++code;
>+    ++code;
> 
>-    X265_CHECK(temp, "writing -1 code, will cause infinite loop\n");
>+    X265_CHECK(code, "writing -1 code, will cause infinite loop\n");
> 
>-    while (1 != temp)
>-    {
>-        temp >>= 1;
>-        length += 2;
>-    }
>+    unsigned long idx;
>+    CLZ(idx, code);
>+    uint32_t length = 1 + (uint32_t)(idx << 1);

'idx * 2 + 1' faster on x86, it mapping to LEA
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.videolan.org/pipermail/x265-devel/attachments/20151110/286f890b/attachment.html>