sysdeps/alpha/strlen.c

   1 /* Copyright (C) 1992 Free Software Foundation, Inc.
   2
   3 The GNU C Library is free software; you can redistribute it and/or
   4 modify it under the terms of the GNU Library General Public License as
   5 published by the Free Software Foundation; either version 2 of the
   6 License, or (at your option) any later version.
   7
   8 The GNU C Library is distributed in the hope that it will be useful,
   9 but WITHOUT ANY WARRANTY; without even the implied warranty of
  10 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11 Library General Public License for more details.
  12
  13 You should have received a copy of the GNU Library General Public
  14 License along with the GNU C Library; see the file COPYING.LIB.  If
  15 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  16 Cambridge, MA 02139, USA.  */
  17
  18 #include <string.h>
  19
  20 /* Return the length of the null-terminated string STR.  Scan for
  21    the null terminator quickly by testing eight bytes at a time.  */
  22
  23 size_t
  24 strlen (const char *str)
  25 {
  26   const char *char_ptr;
  27   const unsigned long int *longword_ptr;
  28
  29   /* Handle the first few characters by reading one character at a time.
  30      Do this until STR is aligned on a 8-byte border.  */
  31   for (char_ptr = str; ((unsigned long int) char_ptr & 7) != 0; ++char_ptr)
  32     if (*char_ptr == '\0')
  33       return char_ptr - str;
  34
  35   longword_ptr = (unsigned long int *) char_ptr;
  36
  37   for (;;)
  38     {
  39       const unsigned long int longword = *longword_ptr++;
  40       int mask;
  41
  42       /* Set bits in MASK if bytes in LONGWORD are zero.  */
  43       asm ("cmpbge $31, %1, %0" : "=r" (mask) : "r" (longword));
  44       if (mask)
  45         {
  46           /* Which of the bytes was the zero?  */
  47           const char *cp = (const char *) (longword_ptr - 1);
  48           int i;
  49
  50           for (i = 0; i < 8; i++)
  51             if (cp[i] == 0)
  52               return cp - str + i;
  53         }
  54     }
  55 }