Hi, On Wed, Oct 14, 2015 at 10:26 AM, Ganesh Ajjanagadde <gajjanaga...@gmail.com > wrote:
> It has already been demonstrated that the de Bruijn method has benefits > over the current implementation: commit > 971d12b7f9d7be3ca8eb98e6c04ed521f83cbd3c. > That commit implemented it for long long, this extends it to the int > version. > > Tested with FATE. > > Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com> > --- > libavutil/intmath.h | 32 +++++++------------------------- > 1 file changed, 7 insertions(+), 25 deletions(-) > > diff --git a/libavutil/intmath.h b/libavutil/intmath.h > index 802abe3..5a55123 100644 > --- a/libavutil/intmath.h > +++ b/libavutil/intmath.h > @@ -129,33 +129,15 @@ static av_always_inline av_const int > ff_log2_16bit_c(unsigned int v) > * @return the number of trailing 0-bits > */ > #if !defined( _MSC_VER ) > +/* We use the De-Bruijn method outlined in: > + * http://supertech.csail.mit.edu/papers/debruijn.pdf. */ > static av_always_inline av_const int ff_ctz_c(int v) > { > - int c; > - > - if (v & 0x1) > - return 0; > - > - c = 1; > - if (!(v & 0xffff)) { > - v >>= 16; > - c += 16; > - } > - if (!(v & 0xff)) { > - v >>= 8; > - c += 8; > - } > - if (!(v & 0xf)) { > - v >>= 4; > - c += 4; > - } > - if (!(v & 0x3)) { > - v >>= 2; > - c += 2; > - } > - c -= v & 0x1; > - > - return c; > + static const uint8_t debruijn_ctz32[32] = { > + 0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, > + 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9 > + }; > + return debruijn_ctz32[(uint32_t)((v & -v) * 0x077CB531U) >> 27]; > } > #else > static av_always_inline av_const int ff_ctz_c( int v ) > -- > 2.6.1 lgtm. Would you like to push yourself or have me do it for you? Ronald _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
