On 1/3/2016 5:33 PM, wm4 wrote:
> On Sun, 3 Jan 2016 20:21:00 +0100
> Clément Bœsch <u...@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?
GCC does on x86 when the target cpu doesn't support the popcnt instruction,
otherwise the end result would be the same (popcnt + and).
av_popcount_c() is not optimal for this.
>
>> +}
>> +
>> #if defined(__BMI2__)
>>
>> #if AV_GCC_VERSION_AT_LEAST(5,1)
>
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