sysdeps/i386/ffs.c

   1 /* ffs -- find first set bit in a word, counted from least significant end.
   2    For Intel 80x86, x>=3.
   3    Copyright (C) 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
   4    Contributed by Torbjorn Granlund (tege@sics.se).
   5
   6 The GNU C Library is free software; you can redistribute it and/or
   7 modify it under the terms of the GNU Library General Public License as
   8 published by the Free Software Foundation; either version 2 of the
   9 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 Library General Public License for more details.
  15
  16 You should have received a copy of the GNU Library General Public
  17 License along with the GNU C Library; see the file COPYING.LIB.  If
  18 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  19 Cambridge, MA 02139, USA.  */
  20
  21 #include <ansidecl.h>
  22 #include <string.h>
  23
  24 #undef  ffs
  25
  26 #ifdef  __GNUC__
  27
  28 int
  29 DEFUN(ffs, (x), int x)
  30 {
  31   int cnt;
  32   int tmp;
  33
  34   asm ("xorl %0,%0\n"           /* Set CNT to zero.  */
  35        "bsfl %2,%1\n"           /* Count low bits in X and store in %1.  */
  36        "jz nonzero\n"           /* Jump if OK, i.e. X was non-zero.  */
  37        "leal 1(%1),%0\n"        /* Return bsfl-result plus one on %0.  */
  38        "nonzero:" : "=&a" (cnt), "=r" (tmp) : "rm" (x));
  39
  40   return cnt;
  41 }
  42
  43 #else
  44 #include <sysdeps/generic/ffs.c>
  45 #endif