[FFmpeg-devel] [PATCH] Better AV_ZERO128 on x86

[Alexander Strange]

On Sat, Jan 15, 2011 at 2:53 AM, Jason Garrett-Glaser <jason at x264.com> wrote:
> This patch makes AV_ZERO work under SSE, instead of requiring SSE2.

Fine here.

The 'struct v's defined in that file need av_alias added sometime, or
need to be moved next to the definition of av_alias64.

>
> But AV_ZERO still sucks, because it duplicates the pxor/xorps every
> single time it runs. ?Is there any reason we can't do what x264 does,
> that is, use intrinsics like ((__m128){0,0,0,0}) to solve the problem?
> ?This does make gcc (even crappy old gcc) reuse the value instead of
> calculating it every time.

I only did it like this to avoid an argument about using intrinsics.

Isn't it actually faster on some cpus to do xor every time, because of
register read stalls?