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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 Intel 80x86, x>=3.
00003    This file is part of the GNU C Library.
00004    Copyright (C) 1991, 92, 93, 94, 97, 98, 2004, 2005 Free Software Foundation, Inc.
00005    Contributed by Torbjorn Granlund (tege@sics.se).
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 #define ffsl __something_else
00023 #include <string.h>
00024 
00025 #undef ffs
00026 
00027 #ifdef __GNUC__
00028 
00029 int
00030 __ffs (x)
00031      int x;
00032 {
00033   int cnt;
00034   int tmp;
00035 
00036   asm ("xorl %0,%0\n"              /* Set CNT to zero.  */
00037        "bsfl %2,%1\n"              /* Count low bits in X and store in %1.  */
00038        "jz 1f\n"            /* Jump if OK, i.e. X was non-zero.  */
00039        "leal 1(%1),%0\n"    /* Return bsfl-result plus one on %0.  */
00040        "1:" : "=&a" (cnt), "=r" (tmp) : "rm" (x));
00041 
00042   return cnt;
00043 }
00044 weak_alias (__ffs, ffs)
00045 libc_hidden_builtin_def (ffs)
00046 #undef ffsl
00047 weak_alias (__ffs, ffsl)
00048 
00049 #else
00050 #include <string/ffs.c>
00051 #endif