Hi, On Wed, Oct 14, 2015 at 1:26 PM, Ganesh Ajjanagadde <gajjanaga...@gmail.com> wrote:
> On Wed, Oct 14, 2015 at 1:13 PM, Ronald S. Bultje <rsbul...@gmail.com> > wrote: > > 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? > > Either way is fine: if it is not done by tonight, I will do it. > Thanks. Pushed :) Ronald _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
