[FFmpeg-devel] Some IWMMXT functions for libavcodec

Dmitry Antipov dmantipov
Sat May 17 17:15:04 CEST 2008

Michael Niedermayer wrote:

> So write code which is near perfect on both

How is it reasonable to implement different specialized version for
each generation of the core like it does with MMX and MMX2?

As we're investigated,

     wldrd wr2, [%1, #8]
     wldrd wr1, [%1], %2

is much better than

     wldrd wr1, [%1]
     wldrd wr2, [%1, #8]
     add %1, %1, %2

but the first version will work on PXA3xx cores only.

Moreover, WMMX2 adds some useful instructions - for example, WAVG4 may
be used to implement very fast pix_abs16_xy2 and pix_abs8_xy2 (which
will not work on PXA2xx cores).


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