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) 1991-2023 Free Software Foundation, Inc.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
19
20#include <string.h>
21
22#undef ffs
23
24int
25__ffs (int x)
26{
27 int cnt;
28 int tmp;
29
30 asm ("bsfl %2,%0\n" /* Count low bits in X and store in %1. */
31 "cmovel %1,%0\n" /* If number was zero, use -1 as result. */
32 : "=&r" (cnt), "=r" (tmp) : "rm" (x), "1" (-1));
33
34 return cnt + 1;
35}
36weak_alias (__ffs, ffs)
37libc_hidden_def (__ffs)
38libc_hidden_builtin_def (ffs)
39