[FFmpeg-devel] [PATCH] x86/intmath: allow the source operand for icc/icl ff_ctzll to be a memory location

James Almer jamrial at gmail.com
Sun Oct 25 01:03:20 CEST 2015


On 10/24/2015 7:48 PM, Ganesh Ajjanagadde wrote:
> On Sat, Oct 24, 2015 at 6:08 PM, James Almer <jamrial at gmail.com> wrote:
>> This gives the compiler some flexibility
>>
>> Signed-off-by: James Almer <jamrial at gmail.com>
>> ---
>>  libavutil/x86/intmath.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/libavutil/x86/intmath.h b/libavutil/x86/intmath.h
>> index 7881e3c..10d3e7f 100644
>> --- a/libavutil/x86/intmath.h
>> +++ b/libavutil/x86/intmath.h
>> @@ -36,7 +36,7 @@ static av_always_inline av_const int ff_ctzll_x86(long long v)
>>  {
>>  #   if ARCH_X86_64
>>      uint64_t c;
>> -    __asm__("bsfq %1,%0" : "=r" (c) : "r" (v));
>> +    __asm__ ("bsfq %1,%0" : "=r" (c) : "rm" (v));
>>      return c;
>>  #   else
>>      return ((uint32_t)v == 0) ? _bit_scan_forward((uint32_t)(v >> 32)) + 32 : _bit_scan_forward((uint32_t)v);
>> --
>> 2.6.2
> 
> This question may be silly, but can you clarify when this asm code is
> used instead of __builtin_ctzll? For instance, I think on GNU/Linux,
> x86-64, sufficiently modern GCC (even with asm enabled), we should
> always use the builtin: the compiler knows best what to do with its
> builtin.

This is ICC/ICL, not GCC.




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