jcs.org
jcs's openbsd hax
openbsd
1/* $OpenBSD: ffs.c,v 1.9 2014/06/10 04:16:57 deraadt Exp $ */
2
3/*
4 * Public domain.
5 * Written by Dale Rahn.
6 */
7
8#include <lib/libkern/libkern.h>
9
10/*
11 * ffs -- vax ffs instruction
12 */
13int
14ffs(int mask)
15{
16 int bit;
17 unsigned int r = mask;
18 static const signed char t[16] = {
19 -28, 1, 2, 1,
20 3, 1, 2, 1,
21 4, 1, 2, 1,
22 3, 1, 2, 1
23 };
24
25 bit = 0;
26 if (!(r & 0xffff)) {
27 bit += 16;
28 r >>= 16;
29 }
30 if (!(r & 0xff)) {
31 bit += 8;
32 r >>= 8;
33 }
34 if (!(r & 0xf)) {
35 bit += 4;
36 r >>= 4;
37 }
38
39 return (bit + t[ r & 0xf ]);
40}