From 754c677b0bbf3ea6c7d2a73c93848f1b0d68c91e Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Mon, 20 Jun 2011 16:54:15 +0930 Subject: lib: import ccan modules for tdb2 Imported from git://git.ozlabs.org/~ccan/ccan init-1161-g661d41f Signed-off-by: Rusty Russell --- lib/ccan/ilog/ilog.c | 139 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 139 insertions(+) create mode 100644 lib/ccan/ilog/ilog.c (limited to 'lib/ccan/ilog/ilog.c') diff --git a/lib/ccan/ilog/ilog.c b/lib/ccan/ilog/ilog.c new file mode 100644 index 0000000000..40c5a6fd50 --- /dev/null +++ b/lib/ccan/ilog/ilog.c @@ -0,0 +1,139 @@ +/*(C) Timothy B. Terriberry (tterribe@xiph.org) 2001-2009 LGPL (v2 or later).*/ +#include "ilog.h" +#include + +/*The fastest fallback strategy for platforms with fast multiplication appears + to be based on de Bruijn sequences~\cite{LP98}. + Tests confirmed this to be true even on an ARM11, where it is actually faster + than using the native clz instruction. + Define ILOG_NODEBRUIJN to use a simpler fallback on platforms where + multiplication or table lookups are too expensive. + + @UNPUBLISHED{LP98, + author="Charles E. Leiserson and Harald Prokop", + title="Using de {Bruijn} Sequences to Index a 1 in a Computer Word", + month=Jun, + year=1998, + note="\url{http://supertech.csail.mit.edu/papers/debruijn.pdf}" + }*/ +static UNNEEDED const unsigned char DEBRUIJN_IDX32[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 +}; + +/* We always compile these in, in case someone takes address of function. */ +#undef ilog32_nz +#undef ilog32 +#undef ilog64_nz +#undef ilog64 + +int ilog32(uint32_t _v){ +/*On a Pentium M, this branchless version tested as the fastest version without + multiplications on 1,000,000,000 random 32-bit integers, edging out a + similar version with branches, and a 256-entry LUT version.*/ +# if defined(ILOG_NODEBRUIJN) + int ret; + int m; + ret=_v>0; + m=(_v>0xFFFFU)<<4; + _v>>=m; + ret|=m; + m=(_v>0xFFU)<<3; + _v>>=m; + ret|=m; + m=(_v>0xFU)<<2; + _v>>=m; + ret|=m; + m=(_v>3)<<1; + _v>>=m; + ret|=m; + ret+=_v>1; + return ret; +/*This de Bruijn sequence version is faster if you have a fast multiplier.*/ +# else + int ret; + ret=_v>0; + _v|=_v>>1; + _v|=_v>>2; + _v|=_v>>4; + _v|=_v>>8; + _v|=_v>>16; + _v=(_v>>1)+1; + ret+=DEBRUIJN_IDX32[_v*0x77CB531U>>27&0x1F]; + return ret; +# endif +} + +int ilog32_nz(uint32_t _v) +{ + return ilog32(_v); +} + +int ilog64(uint64_t _v){ +# if defined(ILOG_NODEBRUIJN) + uint32_t v; + int ret; + int m; + ret=_v>0; + m=(_v>0xFFFFFFFFU)<<5; + v=(uint32_t)(_v>>m); + ret|=m; + m=(v>0xFFFFU)<<4; + v>>=m; + ret|=m; + m=(v>0xFFU)<<3; + v>>=m; + ret|=m; + m=(v>0xFU)<<2; + v>>=m; + ret|=m; + m=(v>3)<<1; + v>>=m; + ret|=m; + ret+=v>1; + return ret; +# else +/*If we don't have a 64-bit word, split it into two 32-bit halves.*/ +# if LONG_MAX<9223372036854775807LL + uint32_t v; + int ret; + int m; + ret=_v>0; + m=(_v>0xFFFFFFFFU)<<5; + v=(uint32_t)(_v>>m); + ret|=m; + v|=v>>1; + v|=v>>2; + v|=v>>4; + v|=v>>8; + v|=v>>16; + v=(v>>1)+1; + ret+=DEBRUIJN_IDX32[v*0x77CB531U>>27&0x1F]; + return ret; +/*Otherwise do it in one 64-bit operation.*/ +# else + static const unsigned char DEBRUIJN_IDX64[64]={ + 0, 1, 2, 7, 3,13, 8,19, 4,25,14,28, 9,34,20,40, + 5,17,26,38,15,46,29,48,10,31,35,54,21,50,41,57, + 63, 6,12,18,24,27,33,39,16,37,45,47,30,53,49,56, + 62,11,23,32,36,44,52,55,61,22,43,51,60,42,59,58 + }; + int ret; + ret=_v>0; + _v|=_v>>1; + _v|=_v>>2; + _v|=_v>>4; + _v|=_v>>8; + _v|=_v>>16; + _v|=_v>>32; + _v=(_v>>1)+1; + ret+=DEBRUIJN_IDX64[_v*0x218A392CD3D5DBF>>58&0x3F]; + return ret; +# endif +# endif +} + +int ilog64_nz(uint64_t _v) +{ + return ilog64(_v); +} -- cgit