[FFmpeg-devel] [PATCH] Port extra x264 CPU detection code

[Ronald S. Bultje]

Hi,

On Fri, Jan 9, 2009 at 9:21 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> On Wed, Jan 07, 2009 at 11:46:59AM -0500, Jason Garrett-Glaser wrote:
>> +        if( !strcmp((char*)vendor, "GenuineIntel") ){
>> +            int family, model, stepping;
>> +            family = ((eax>>8)&0xf) + ((eax>>20)&0xff);
>> +            model  = ((eax>>4)&0xf) + ((eax>>12)&0xf0);
>> +            stepping = eax&0xf;
>> +            /* 6/9 (pentium-m "banias"), 6/13 (pentium-m "dothan"), and 6/14 (core1 "yonah")
>> +             * theoretically support sse2, but it's significantly slower than mmx for
>> +             * basically all functions, so let's just pretend they don't. */
>> +            if( family==6 && (model==9 || model==13 || model==14) ){
>> +                rval &= ~FF_MM_SSE2;
>> +                assert(!(rval&FF_MM_SSSE3));
>> +            }
>> +        }
>>      }
>>
>>      cpuid(0x80000000, max_ext_level, ebx, ecx, edx);
>
> i am not entirly happy about lying about the supported feature set.
> Though iam not rejecting this, rather i abstain from approving it,
> if the others think this is ok so am i with it if not then not.

Can't you just introduce a flag "SSE2_IS_ACTUALLY_FASTER_THAN_MMX" or
the opposite and use an if() to mark functions that are slower on
these particular CPUs with SSE2 than MMX as such and therefore get the
best of both worlds, including support for the ~1 SSE2 function where
SSE2 does actually beat MMX on these CPUs?

Just a silly suggestion.

Ronald