1 /* ffs -- find first set bit in a word, counted from least significant end.
2 For Intel 80x86, x>=3.
3 This file is part of the GNU C Library.
4 Copyright (C) 1991-2022 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 #define ffsl __something_else
21 #include <string.h>
22
23 #undef ffs
24
25 #ifdef __GNUC__
26
27 int
__ffs(int x)28 __ffs (int x)
29 {
30 int cnt;
31 int tmp;
32
33 asm ("xorl %0,%0\n" /* Set CNT to zero. */
34 "bsfl %2,%1\n" /* Count low bits in X and store in %1. */
35 "jz 1f\n" /* Jump if OK, i.e. X was non-zero. */
36 "leal 1(%1),%0\n" /* Return bsfl-result plus one on %0. */
37 "1:" : "=&a" (cnt), "=r" (tmp) : "rm" (x));
38
39 return cnt;
40 }
41 weak_alias (__ffs, ffs)
42 libc_hidden_def (__ffs)
43 libc_hidden_builtin_def (ffs)
44 #undef ffsl
45 weak_alias (__ffs, ffsl)
46
47 #else
48 #include <string/ffs.c>
49 #endif
50