1/* ffs -- find first set bit in a word, counted from least significant end.
2 For AMD x86-64.
3 This file is part of the GNU C Library.
4 Copyright (C) 1991-2020 Free Software Foundation, Inc.
5 Contributed by Ulrich Drepper <drepper@cygnus.com>.
6
7 The GNU C Library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public
9 License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version.
11
12 The GNU C Library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License for more details.
16
17 You should have received a copy of the GNU Lesser General Public
18 License along with the GNU C Library; if not, see
19 <https://www.gnu.org/licenses/>. */
20
21#include <string.h>
22
23#undef ffs
24
25int
26__ffs (int x)
27{
28 int cnt;
29 int tmp;
30
31 asm ("bsfl %2,%0\n" /* Count low bits in X and store in %1. */
32 "cmovel %1,%0\n" /* If number was zero, use -1 as result. */
33 : "=&r" (cnt), "=r" (tmp) : "rm" (x), "1" (-1));
34
35 return cnt + 1;
36}
37weak_alias (__ffs, ffs)
38libc_hidden_def (__ffs)
39libc_hidden_builtin_def (ffs)
40