[Ffmpeg-devel] Re: idct_mmi.c license in FFmpeg

Michel Lespinasse walken
Tue Sep 5 05:49:53 CEST 2006

On Mon, Sep 04, 2006 at 06:44:04PM +0200, leon wrote:
> Michel's rounding trick actually is probably no longer used, but i
> couldn't find what the trick exactly was at that time.
> For safety (IANAL) i just included the copyright statements of the 
> original mmx version in this mmi version.
> http://noomore.org/stuff/playstation2/psidct/idct8x8_xmm.html.txt

FYI the rounding trick is present in the noomore version as the
rounder_0 .. rounter_7 values.

I believe Intel code used and/or instructions to set/clear the LSB bit
in some places to avoid IDCT bias. This also had an impact on IDCT
accuracy however.

Michel "Walken" Lespinasse
"Bill Gates is a monocle and a Persian cat away from being the villain
in a James Bond movie." -- Dennis Miller

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