1/* ffs.c - find first set bit */
2/* ffs() is defined by Single Unix Specification. */
3
4#include "ruby.h"
5
6int ffs(int arg)
7{
8    unsigned int x = (unsigned int)arg;
9    int r;
10
11    if (x == 0)
12        return 0;
13
14    r = 1;
15
16#if 32 < SIZEOF_INT * CHAR_BIT
17    if ((x & 0xffffffff) == 0) {
18        x >>= 32;
19        r += 32;
20    }
21#endif
22
23    if ((x & 0xffff) == 0) {
24        x >>= 16;
25        r += 16;
26    }
27
28    if ((x & 0xff) == 0) {
29        x >>= 8;
30        r += 8;
31    }
32
33    if ((x & 0xf) == 0) {
34        x >>= 4;
35        r += 4;
36    }
37
38    if ((x & 0x3) == 0) {
39        x >>= 2;
40        r += 2;
41    }
42
43    if ((x & 0x1) == 0) {
44        x >>= 1;
45        r += 1;
46    }
47
48    return r;
49}
50