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

[Henrik Gramner]

On Sun, Oct 25, 2015 at 5:39 PM, Matt Oliver <protogonoi at gmail.com> wrote:
> Using tzcnt would be the more interesting option. Changing the asm to tzcnt
> works with ICL. But also the use of the tzcnt intrinsic (_tzcnt_u64) would
> be possible with both intel and msvc. I dont have anything older than
> Haswell or Piledriver to double check but I have seen its use in several
> other projects without issue so in theory it shouldnt be a problem.

IIRC tzcnt (rep bsf) is only slower than plain bsf on really ancient
machines, e.g. 80486 and such, so there's not really any downside of
using it.