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glibc  2.9
ffs.c
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00001 /* Copyright (C) 1991, 1992, 1997, 1998, 2004 Free Software Foundation, Inc.
00002    This file is part of the GNU C Library.
00003    Contributed by Torbjorn Granlund (tege@sics.se).
00004 
00005    The GNU C Library is free software; you can redistribute it and/or
00006    modify it under the terms of the GNU Lesser General Public
00007    License as published by the Free Software Foundation; either
00008    version 2.1 of the License, or (at your option) any later version.
00009 
00010    The GNU C Library is distributed in the hope that it will be useful,
00011    but WITHOUT ANY WARRANTY; without even the implied warranty of
00012    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00013    Lesser General Public License for more details.
00014 
00015    You should have received a copy of the GNU Lesser General Public
00016    License along with the GNU C Library; if not, write to the Free
00017    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00018    02111-1307 USA.  */
00019 
00020 #include <limits.h>
00021 #define ffsl __something_else
00022 #include <string.h>
00023 
00024 #undef ffs
00025 
00026 /* Find the first bit set in I.  */
00027 int
00028 __ffs (i)
00029      int i;
00030 {
00031   static const unsigned char table[] =
00032     {
00033       0,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
00034       6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
00035       7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
00036       7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
00037       8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
00038       8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
00039       8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
00040       8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8
00041     };
00042   unsigned int a;
00043   unsigned int x = i & -i;
00044 
00045   a = x <= 0xffff ? (x <= 0xff ? 0 : 8) : (x <= 0xffffff ?  16 : 24);
00046 
00047   return table[x >> a] + a;
00048 }
00049 weak_alias (__ffs, ffs)
00050 libc_hidden_builtin_def (ffs)
00051 
00052 #if ULONG_MAX == UINT_MAX
00053 #undef ffsl
00054 weak_alias (__ffs, ffsl)
00055 #endif