[FFmpeg-devel] [PATCH 1/2] Fix miscompilation for i586.

[Michael Niedermayer]

Hi

On Fri, Sep 12, 2014 at 09:49:30PM +0200, Mikulas Patocka wrote:
> Hi
> 
> Here I'm sending two patches to fix portability for 586-class machines 
> (Pentium, K6, etc.)
> 
> 
> If the CPU is generic, 386, 486 or pentium, we must not use cmov in inline
> assembler.
> 
[...]
>
> ---
>  configure                |    4 ++++
>  libavcodec/x86/mathops.h |    2 +-
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> Index: ffmpeg/configure
> ===================================================================
> --- ffmpeg.orig/configure	2014-09-12 21:46:25.710512294 +0200
> +++ ffmpeg/configure	2014-09-12 21:46:32.099587711 +0200
> @@ -3840,8 +3840,12 @@ elif enabled sparc; then
[...]
>          i[345]86|pentium)
>              cpuflags="-march=$cpu"
> +            disable i686
>              disable mmx
>          ;;
>          # targets that do NOT support nopl and conditional mov (cmov)

applied this

for the rest, please see james and hendriks replies

also, maybe you want to setup a i586 fate client, so these issues
are detected quicker ?
See: http://ffmpeg.org/fate.html

Thanks


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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