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glibc  2.9
ffs.c
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00001 /* ffs -- find first set bit in a word, counted from least significant end.
00002    For AMD x86-64.
00003    This file is part of the GNU C Library.
00004    Copyright (C) 1991,92,93,94,97,98,2001,2004 Free Software Foundation, Inc.
00005    Contributed by Ulrich Drepper <drepper@cygnus.com>.
00006 
00007    The GNU C Library is free software; you can redistribute it and/or
00008    modify it under the terms of the GNU Lesser General Public
00009    License as published by the Free Software Foundation; either
00010    version 2.1 of the License, or (at your option) any later version.
00011 
00012    The GNU C Library is distributed in the hope that it will be useful,
00013    but WITHOUT ANY WARRANTY; without even the implied warranty of
00014    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015    Lesser General Public License for more details.
00016 
00017    You should have received a copy of the GNU Lesser General Public
00018    License along with the GNU C Library; if not, write to the Free
00019    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00020    02111-1307 USA.  */
00021 
00022 #include <string.h>
00023 
00024 #undef ffs
00025 
00026 int
00027 __ffs (int x)
00028 {
00029   int cnt;
00030   int tmp;
00031 
00032   asm ("bsfl %2,%0\n"              /* Count low bits in X and store in %1.  */
00033        "cmovel %1,%0\n"            /* If number was zero, use -1 as result.  */
00034        : "=&r" (cnt), "=r" (tmp) : "rm" (x), "1" (-1));
00035 
00036   return cnt + 1;
00037 }
00038 weak_alias (__ffs, ffs)
00039 libc_hidden_builtin_def (ffs)