[FFmpeg-devel] [PATCH] Optimisations for av_log2 and integer clip functions
Thu Jan 14 10:20:48 CET 2010
On 14.01.2010 09:59, Reimar D?ffinger wrote:
> On Thu, Jan 14, 2010 at 06:33:44AM +0300, Yuriy Kaminskiy wrote:
>> On 14.01.2010 03:31, M?ns Rullg?rd wrote:
>>> Michael Niedermayer <michaelni at gmx.at> writes:
>>>> On Wed, Jan 13, 2010 at 05:55:26PM -0500, Jason Garrett-Glaser wrote:
>>>> If thats to easy one also could factor the question in about the speed
>>>> difference actually making a difference for a file a user wants to play
>>> Perhaps someone with an AMD processor could try the patch on a flac file.
>> amd k8 - x2 4850e, 32bit, gcc-4.1.2, -march=pentium3 -mtune=k8
>> mplayer -nocache -ao pcm:fast:nowaveheader:file=/dev/null *.flac
>> before: user 0m7.140s (best of few runs)
>> after: user 0m8.085s
> Is that with Michael's optimization which avoids the comparison?
> Might make a relevant difference...
This one - without. Unfortunately, it make almost zero difference:
- return v? 31 - __builtin_clz(v) : 0;
+ return 31 - __builtin_clz(v | 1);
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