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-rw-r--r--contrib/ccan/ilog/ilog.c141
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diff --git a/contrib/ccan/ilog/ilog.c b/contrib/ccan/ilog/ilog.c
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+/*(C) Timothy B. Terriberry (tterribe@xiph.org) 2001-2009 CC0 (Public domain).
+ * See LICENSE file for details. */
+#include "ilog.h"
+#include <limits.h>
+
+/*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+ @UNPUBLISHED{LP98,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);
+}
+