sysdeps/i386/strlen.c

   1 /* Determine the length of a string.  For Intel 80x86, x>=3.
   2    Copyright (C) 1991-2017 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   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 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    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <string.h>
  21
  22 size_t
  23 strlen (const char *str)
  24 {
  25   int cnt;
  26
  27   asm("cld\n"                   /* Search forward.  */
  28       /* Some old versions of gas need `repne' instead of `repnz'.  */
  29       "repnz\n"                 /* Look for a zero byte.  */
  30       "scasb" /* %0, %1, %3 */ :
  31       "=c" (cnt) : "D" (str), "0" (-1), "a" (0));
  32
  33   return -2 - cnt;
  34 }
  35 libc_hidden_builtin_def (strlen)