[Mplayer-dev-eng] idct accepted =) Fwd: Re: [Ffmpeg-devel] mmx idct

[Arpi]

--------- Forwarded message ---------
From: "Gérard" Lantau <glantau at yahoo.fr>
To: arpi at thot.banki.hu
Subject: Re: [Ffmpeg-devel] mmx idct

Thank you for the mmx idct opt! Can you discuss with its author (Michel
LESPINASSE ?) so that I can include it in libavcodec while having an LGPL
license ? 

I submitted a list of ideas optimization a few days ago and I think each of
these should add some non negligible speed up while leading to reasonnably
readable and generic code (so that all codecs can benefit from these
optimizations) :

>- frame copy optimization : I'll add the external frame alloc so that we can
>avoid on frame copy (we will be able to compare to latest opendivx).
>- DCT : by using an mmx DCT we should have an important win.
>- h263 mmx dequantize : should be faster than mpeg1 mmx dequantize (NOTE:
msmpeg4 *does* use h263 dequantize)
>- optimize get_vlc() and get_bits() by inlining all that code and doing bit
>parsing "by hand" for short codes (when codes are shorter, they come more
>often, so we can only optimize this case).
>- avoid one memory copy for each MB by using the method I described in one
>previous mail (do motion estimation + DCT adding in same put_pixels_xxx).
>- factorize DCT and dequant (avoid two memory accesses per coef).

The VLC decoding opt can be done in pure C. I won't accept assembly for this
unless I can see a huge speed improvement. inlining get_bits and get_vlc
functions with local bitbuf and bitcnt variables should be sufficient.

The mmx h263 dequant opt is important because it would suppress one memory
access per coefficient. Do you want that I code it ?

Gerard.

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