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[glibc.git] / sysdeps / i386 / ffs.c
blobf53bdd1c160cd8002d1a43c35963ee14e269acb4
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, 92, 93, 94, 97, 98, 2004, 2005 Free Software Foundation, Inc.
5 Contributed by Torbjorn Granlund (tege@sics.se).
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.
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.
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 <http://www.gnu.org/licenses/>. */
21 #define ffsl __something_else
22 #include <string.h>
24 #undef ffs
26 #ifdef __GNUC__
28 int
29 __ffs (x)
30 int x;
32 int cnt;
33 int tmp;
35 asm ("xorl %0,%0\n" /* Set CNT to zero. */
36 "bsfl %2,%1\n" /* Count low bits in X and store in %1. */
37 "jz 1f\n" /* Jump if OK, i.e. X was non-zero. */
38 "leal 1(%1),%0\n" /* Return bsfl-result plus one on %0. */
39 "1:" : "=&a" (cnt), "=r" (tmp) : "rm" (x));
41 return cnt;
43 weak_alias (__ffs, ffs)
44 libc_hidden_builtin_def (ffs)
45 #undef ffsl
46 weak_alias (__ffs, ffsl)
48 #else
49 #include <string/ffs.c>
50 #endif