ffs.c
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/* ffs.c - find first set bit */
/* ffs() is defined by Single Unix Specification. */
#include "ruby.h"
int ffs(int arg)
{
unsigned int x = (unsigned int)arg;
int r;
if (x == 0)
return 0;
r = 1;
#if 32 < SIZEOF_INT * CHAR_BIT
if ((x & 0xffffffff) == 0) {
x >>= 32;
r += 32;
}
#endif
if ((x & 0xffff) == 0) {
x >>= 16;
r += 16;
}
if ((x & 0xff) == 0) {
x >>= 8;
r += 8;
}
if ((x & 0xf) == 0) {
x >>= 4;
r += 4;
}
if ((x & 0x3) == 0) {
x >>= 2;
r += 2;
}
if ((x & 0x1) == 0) {
x >>= 1;
r += 1;
}
return r;
}