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

[Michel Lespinasse]

On Tue, Sep 05, 2006 at 12:00:51PM +0200, leon wrote:
> At the time i was assuming that there was more to the trick than just 
> adding 0.5 (fixed point) before right-shifting it. If not, then yes, 
> this is still included in the mmi version. The actual rounding values 
> made me suspect there was more going on ; after a lot of reshufling of 
> the code and measuring the accuracy, the rounding values are now also 
> different btw.

Since you've been able to recalculate the values after adjusting the code,
you must have figured out what the trick is.

Before that people used to fudge the 16-bit values in the column IDCT to
avoid IDCT bias. The rounder trick replaces that.

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