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si_log2.h
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#ifndef SI_LOG2_H
#define SI_LOG2_H
#include "factory/factoryconf.h"
// stolen from:
// https://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
static inline int SI_LOG2(int v)
{
const unsigned int b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
const unsigned int S[] = {1, 2, 4, 8, 16};
unsigned int r = 0; // result of log2(v) will go here
if (v & b[4]) { v >>= S[4]; r |= S[4]; }
if (v & b[3]) { v >>= S[3]; r |= S[3]; }
if (v & b[2]) { v >>= S[2]; r |= S[2]; }
if (v & b[1]) { v >>= S[1]; r |= S[1]; }
if (v & b[0]) { v >>= S[0]; r |= S[0]; }
return (int)r;
}
#if SIZEOF_LONG==4
#define SI_LOG2_LONG(A) SI_LOG2(A)
#else
static inline int SI_LOG2_LONG(long v)
{
const unsigned long b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000, 0xFFFFFFFF00000000UL};
const unsigned int S[] = {1, 2, 4, 8, 16, 32};
unsigned int r = 0; // result of log2(v) will go here
if (v & b[5]) { v >>= S[5]; r |= S[5]; }
if (v & b[4]) { v >>= S[4]; r |= S[4]; }
if (v & b[3]) { v >>= S[3]; r |= S[3]; }
if (v & b[2]) { v >>= S[2]; r |= S[2]; }
if (v & b[1]) { v >>= S[1]; r |= S[1]; }
if (v & b[0]) { v >>= S[0]; r |= S[0]; }
return (int)r;
}
#endif
#endif
b
CanonicalForm b
Definition cfModGcd.cc:4111
v
const Variable & v
< [in] a sqrfree bivariate poly
Definition facBivar.h:39
factoryconf.h
factoryconf.h' serves as a configuration file for the installed source files (templates and factory....
SI_LOG2
static int SI_LOG2(int v)
Definition si_log2.h:6
SI_LOG2_LONG
static int SI_LOG2_LONG(long v)
Definition si_log2.h:22