[FFmpeg-devel] [PATCH 1/3] common: add ff_parity()

[Clément Bœsch]

On Sun, Jan 03, 2016 at 05:54:34PM -0300, James Almer wrote:
> On 1/3/2016 4:22 PM, Clément Bœsch wrote:
> > On Sun, Jan 03, 2016 at 08:21:00PM +0100, Clément Bœsch wrote:
> > [...]
> >> +static av_always_inline av_const int ff_parity(uint32_t v)
> >> +{
> >> +#if HAVE_PARITY
> >> +    return __builtin_parity(v);
> >> +#else
> >> +    return av_popcount(v) & 1;
> > 
> > doing a popcount being overkill, this could be replaced with
> > (0x6996966996696996ULL >> (x & 63) ^ (x>>7) ^ (x>>6)) & 1
> 
> Are you sure that's correct for an uint32_t?
> 

Erm. Yeah no, my bad.

> > 
> > Whatever people prefers
> 
> No need for the configure check. Make the above the c generic version (Add it to
> common.h or intmath.h), then on x86/intmath.h make it use __builtin_parity if
> __GNU__ is true.

Why should we use __builtin_parity only on x86?

[...]

-- 
Clément B.
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