[FFmpeg-devel] [PATCH v4] lavc/rawdec: Use AV_PIX_FMT_PAL8 for 1-bit raw QuickTime video

Mats Peterson matsp888 at yahoo.com
Mon Jan 18 12:37:58 CET 2016

On 01/18/2016 12:35 PM, Michael Niedermayer wrote:
>> Pure logic tells me it's faster to just increment than involve a
>> series of multiplications.
> its not so simple
> theres a optimizing compiler between you and the CPU
> the multiplication is a shift really, and the compiler may very well
> change this to dst++, buf++ and buf < buf_end
> or it might use something like p[8*i] and q[i]
> i++ and a i<=0 check, the 8* can on some architectures be free as
> part of addressing memory
> if you are interrested in optimizing code see
> http://www.agner.org/optimize/
> and intels Intel 64 and IA-32 Architectures Software Developers Manual
> is invaluable as a reference but not useable for other purposes than
> as a reference (its too huge)

I almost expected that answer, Michael. And I do know there's a lot 
going on behind the scenes. But how much is another question. And don't 
you think it's cleaner to just increment a variable here? Or should I 
revert to the old stuff?


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