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)