On Sun, Oct 25, 2015 at 11:26 AM, Matt Oliver <protogo...@gmail.com> wrote:
> On 25 October 2015 at 12:22, Ganesh Ajjanagadde <gajja...@mit.edu> wrote:
>
>> On Sat, Oct 24, 2015 at 7:03 PM, James Almer <jamr...@gmail.com> wrote:
>> > On 10/24/2015 7:48 PM, Ganesh Ajjanagadde wrote:
>> >> On Sat, Oct 24, 2015 at 6:08 PM, James Almer <jamr...@gmail.com> wrote:
>> >>> This gives the compiler some flexibility
>> >>>
>> >>> Signed-off-by: James Almer <jamr...@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.
>>
>> Ah, now I recall that _bit_scan_forward64 was not always available on
>> ICC. Anyway, this is just a heads up to whoever uses ICC/ICL and the
>> like: you may want to find out to which versions this built in
>> applies.
>
>
> bit_scan_forward64 isnt available on ICL at all, hence the use of asm.
>
Intels intrinsic guide lists _BitScanForward64 as the intrinsic to use, however.
https://software.intel.com/sites/landingpage/IntrinsicsGuide/#techs=Other&expand=373
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
