glibc/sysdeps/i386/strlen.c

/* Determine the length of a string.  For Intel 80x86, x>=3.
   Copyright (C) 1991, 1992, 1993, 1996, 1997 Free Software Foundation, Inc.
   Contributed by Torbjorn Granlund (tege@sics.se).

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <string.h>

size_t
strlen (const char *str)
{
  int cnt;

  asm("cld\n"			/* Search forward.  */
      /* Some old versions of gas need `repne' instead of `repnz'.  */
      "repnz\n"			/* Look for a zero byte.  */
      "scasb" /* %0, %1, %3 */ :
      "=c" (cnt) : "D" (str), "0" (-1), "a" (0));

  return -2 - cnt;
}