39 lines
593 B
C
39 lines
593 B
C
#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include "entcode.h"
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int ec_ilog(ec_uint32 _v){
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#if defined(EC_CLZ)
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return EC_CLZ0-EC_CLZ(_v);
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#else
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/*On a Pentium M, this branchless version tested as the fastest on
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1,000,000,000 random 32-bit integers, edging out a similar version with
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branches, and a 256-entry LUT version.*/
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int ret;
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int m;
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ret=!!_v;
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m=!!(_v&0xFFFF0000)<<4;
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_v>>=m;
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ret|=m;
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m=!!(_v&0xFF00)<<3;
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_v>>=m;
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ret|=m;
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m=!!(_v&0xF0)<<2;
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_v>>=m;
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ret|=m;
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m=!!(_v&0xC)<<1;
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_v>>=m;
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ret|=m;
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ret+=!!(_v&0x2);
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return ret;
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#endif
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}
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