[theora-dev] MMX and extended-MMX acceleration patch for encoding

Rodolphe Ortalo ortalo at laas.fr
Sun May 11 15:09:54 PDT 2003


I've just tried to play with GCC 3.2 (which includes C builtins functions
and types to use MMX instructions) and I've noticed that, with this new
version of GCC, my original MMX patch breaks theora.
 Apparently, GCC 3 handles some type casts differently, and, when using
this compiler, theora encoding process is incorrect. (The primary symptom
is that file sizes increase suddently.) I do not know if this is due only
to my patch modifications (the additional C functions in particular) or if
such problems occur with the original theora code currently in CVS too.

So, my MMX patch should probably be used with a lot of care with GCC
3, and probably only with GCC 2.95. I am currently trying to change it
anyway to work with GCC 3.2 MMX-oriented extensions.

I all cases, I strongly suggest that theora developers try also to use GCC
3.2 with the original C code (and probably also with -Werror and
-pedantic) to see if this new compiler does not reveal old typecasts
subtleties... :-)


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