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. > > Ronald _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
