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

[wm4]

On Sun,  3 Jan 2016 20:21:00 +0100
Clément Bœsch <u at pkh.me> wrote:

> ---
>  configure               | 2 ++
>  libavutil/x86/intmath.h | 9 +++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/configure b/configure
> index 6710f85..610be92 100755
> --- a/configure
> +++ b/configure
> @@ -1738,6 +1738,7 @@ BUILTIN_LIST="
>      machine_rw_barrier
>      MemoryBarrier
>      mm_empty
> +    parity
>      rdtsc
>      sarestart
>      sync_val_compare_and_swap
> @@ -5242,6 +5243,7 @@ check_builtin sarestart signal.h "SA_RESTART"
>  check_builtin sync_val_compare_and_swap "" "int *ptr; int oldval, newval; __sync_val_compare_and_swap(ptr, oldval, newval)"
>  check_builtin gmtime_r time.h "time_t *time; struct tm *tm; gmtime_r(time, tm)"
>  check_builtin localtime_r time.h "time_t *time; struct tm *tm; localtime_r(time, tm)"
> +check_builtin parity "" "__builtin_parity(123)"
>  
>  case "$custom_allocator" in
>      jemalloc)
> diff --git a/libavutil/x86/intmath.h b/libavutil/x86/intmath.h
> index 611ef88..9c36bf2 100644
> --- a/libavutil/x86/intmath.h
> +++ b/libavutil/x86/intmath.h
> @@ -75,6 +75,15 @@ static av_always_inline av_const int ff_ctzll_x86(long long v)
>  
>  #endif /* __POPCNT__ */
>  
> +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;
> +#endif

Do compilers really generate better code for the former?

> +}
> +
>  #if defined(__BMI2__)
>  
>  #if AV_GCC_VERSION_AT_LEAST(5,1)