1  /* ffsll -- find first set bit in a word, counted from least significant end.
       2     For AMD x86-64.
       3     This file is part of the GNU C Library.
       4     Copyright (C) 1991-2023 Free Software Foundation, Inc.
       5  
       6     The GNU C Library is free software; you can redistribute it and/or
       7     modify it under the terms of the GNU Lesser General Public
       8     License as published by the Free Software Foundation; either
       9     version 2.1 of the 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     Lesser General Public License for more details.
      15  
      16     You should have received a copy of the GNU Lesser General Public
      17     License along with the GNU C Library; if not, see
      18     <https://www.gnu.org/licenses/>.  */
      19  
      20  #define ffsl __something_else
      21  #include <string.h>
      22  
      23  #undef	ffsll
      24  
      25  int
      26  ffsll (long long int x)
      27  {
      28    long long int cnt;
      29    long long int tmp;
      30  
      31    asm ("bsfq %2,%0\n"		/* Count low bits in X and store in %1.  */
      32         "cmoveq %1,%0\n"		/* If number was zero, use -1 as result.  */
      33         : "=&r" (cnt), "=r" (tmp) : "rm" (x), "1" (-1));
      34  
      35    return cnt + 1;
      36  }
      37  
      38  #ifndef __ILP32__
      39  #undef	ffsl
      40  weak_alias (ffsll, ffsl)
      41  #endif