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si_log2.h
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1#ifndef SI_LOG2_H
2#define SI_LOG2_H
3#include "factory/factoryconf.h"
4// stolen from:
5// https://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
6static inline int SI_LOG2(int v)
7{
8 const unsigned int b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
9 const unsigned int S[] = {1, 2, 4, 8, 16};
10
11 unsigned int r = 0; // result of log2(v) will go here
12 if (v & b[4]) { v >>= S[4]; r |= S[4]; }
13 if (v & b[3]) { v >>= S[3]; r |= S[3]; }
14 if (v & b[2]) { v >>= S[2]; r |= S[2]; }
15 if (v & b[1]) { v >>= S[1]; r |= S[1]; }
16 if (v & b[0]) { v >>= S[0]; r |= S[0]; }
17 return (int)r;
18}
19#if SIZEOF_LONG==4
20#define SI_LOG2_LONG(A) SI_LOG2(A)
21#else
22static inline int SI_LOG2_LONG(long v)
23{
24 const unsigned long b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000, 0xFFFFFFFF00000000UL};
25 const unsigned int S[] = {1, 2, 4, 8, 16, 32};
26
27 unsigned int r = 0; // result of log2(v) will go here
28 if (v & b[5]) { v >>= S[5]; r |= S[5]; }
29 if (v & b[4]) { v >>= S[4]; r |= S[4]; }
30 if (v & b[3]) { v >>= S[3]; r |= S[3]; }
31 if (v & b[2]) { v >>= S[2]; r |= S[2]; }
32 if (v & b[1]) { v >>= S[1]; r |= S[1]; }
33 if (v & b[0]) { v >>= S[0]; r |= S[0]; }
34 return (int)r;
35}
36#endif
37#endif
CanonicalForm b
Definition: cfModGcd.cc:4103
const Variable & v
< [in] a sqrfree bivariate poly
Definition: facBivar.h:39
static int SI_LOG2(int v)
Definition: si_log2.h:6
static int SI_LOG2_LONG(long v)
Definition: si_log2.h:22