string/strlen.c

   1 /* Copyright (C) 1991-2023 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <libc-pointer-arith.h>
  19 #include <string-fzb.h>
  20 #include <string-fzc.h>
  21 #include <string-fzi.h>
  22 #include <string-shift.h>
  23 #include <string.h>
  24
  25 #ifdef STRLEN
  26 # define __strlen STRLEN
  27 #endif
  28
  29 /* Return the length of the null-terminated string STR.  Scan for
  30    the null terminator quickly by testing four bytes at a time.  */
  31 size_t
  32 __strlen (const char *str)
  33 {
  34   /* Align pointer to sizeof op_t.  */
  35   const uintptr_t s_int = (uintptr_t) str;
  36   const op_t *word_ptr = (const op_t*) PTR_ALIGN_DOWN (str, sizeof (op_t));
  37
  38   op_t word = *word_ptr;
  39   find_t mask = shift_find (find_zero_all (word), s_int);
  40   if (mask != 0)
  41     return index_first (mask);
  42
  43   do
  44     word = *++word_ptr;
  45   while (! has_zero (word));
  46
  47   return ((const char *) word_ptr) + index_first_zero (word) - str;
  48 }
  49 #ifndef STRLEN
  50 weak_alias (__strlen, strlen)
  51 libc_hidden_builtin_def (strlen)
  52 #endif