sysdeps/i386/strlen.c

   1 /* Determine the length of a string.  For Intel 80x86, x>=3.
   2    Copyright (C) 1991-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <string.h>
  20
  21 size_t
  22 strlen (const char *str)
  23 {
  24   int cnt;
  25
  26   asm("cld\n"                   /* Search forward.  */
  27       /* Some old versions of gas need `repne' instead of `repnz'.  */
  28       "repnz\n"                 /* Look for a zero byte.  */
  29       "scasb" /* %0, %1, %3 */ :
  30       "=c" (cnt) : "D" (str), "0" (-1), "a" (0));
  31
  32   return -2 - cnt;
  33 }
  34 libc_hidden_builtin_def (strlen)