[FFmpeg-devel] Pipeline: H.264 speed improvements

Guillaume POIRIER poirierg
Wed Dec 24 01:40:05 CET 2008


On Wed, Dec 24, 2008 at 12:02 AM, Jason Garrett-Glaser
<darkshikari at gmail.com> wrote:
> For ARM this can be special-cased.  Intel CPUs have a 1-3 cycle CLZ
> (depends on the CPU) but on AMD chips this can cost >10 cycles, so a
> table is generally preferred on x86.

The PPC970 (aka G5) has a 2 cycle latency for cntlzw and can do 2 of
these per cycle.
The PPC7450 (aka G4) has a 1 cycle latency.

Note that to the best of my knowledge, there's no PPC inline assembly
in FFmpeg, so this information is quite theoretical, all the most
since I never wrote a single PPC function in assembly.

Only a very small fraction of our DNA does anything; the rest is all
comments and ifdefs.

Lily Tomlin  - "I always wanted to be somebody, but now I realize I
should have been more specific."

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