[x264-devel] Re: [patch] mmxext optimized 8x8 block transforms (sub8_dct8/add8_idct8)

[Loren Merritt]

On Thu, 25 Aug 2005, Christian Heine wrote:

> btw. I noticed that the C sub8x8_dct8 isn't exactly the inverse of
> add8x8_idct8. I wonder if this is really intended ( to add
> compressability with quant/dequant perhaps ) or just a bug.

It is intended, and applies to 4x4 transform too. dct/idct expect 
different coefficients to be scaled by different amounts, as convenient 
for a fast implementation (and in idct, mandated by the standard). The 
rescaling is absorbed into the quant/dequant phase.

--Loren Merritt

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