1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
|
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "entcode.h"
int ec_ilog(ec_uint32 _v){
#if defined(EC_CLZ)
return EC_CLZ0-EC_CLZ(_v);
#else
/*On a Pentium M, this branchless version tested as the fastest on
1,000,000,000 random 32-bit integers, edging out a similar version with
branches, and a 256-entry LUT version.*/
int ret;
int m;
ret=!!_v;
m=!!(_v&0xFFFF0000)<<4;
_v>>=m;
ret|=m;
m=!!(_v&0xFF00)<<3;
_v>>=m;
ret|=m;
m=!!(_v&0xF0)<<2;
_v>>=m;
ret|=m;
m=!!(_v&0xC)<<1;
_v>>=m;
ret|=m;
ret+=!!(_v&0x2);
return ret;
#endif
}
int ec_ilog64(ec_uint64 _v){
#if defined(EC_CLZ64)
return EC_CLZ64_0-EC_CLZ64(_v);
#else
ec_uint32 v;
int ret;
int m;
ret=!!_v;
m=!!(_v&((ec_uint64)0xFFFFFFFF)<<32)<<5;
v=(ec_uint32)(_v>>m);
ret|=m;
m=!!(v&0xFFFF0000)<<4;
v>>=m;
ret|=m;
m=!!(v&0xFF00)<<3;
v>>=m;
ret|=m;
m=!!(v&0xF0)<<2;
v>>=m;
ret|=m;
m=!!(v&0xC)<<1;
v>>=m;
ret|=m;
ret+=!!(v&0x2);
return ret;
#endif
}
|
