arch/tile/lib/strlen_32.c

   1 /*
   2  * Copyright 2010 Tilera Corporation. All Rights Reserved.
   3  *
   4  *   This program is free software; you can redistribute it and/or
   5  *   modify it under the terms of the GNU General Public License
   6  *   as published by the Free Software Foundation, version 2.
   7  *
   8  *   This program is distributed in the hope that it will be useful, but
   9  *   WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  11  *   NON INFRINGEMENT.  See the GNU General Public License for
  12  *   more details.
  13  */
  14
  15 #include <linux/types.h>
  16 #include <linux/string.h>
  17 #include <linux/module.h>
  18
  19 size_t strlen(const char *s)
  20 {
  21         /* Get an aligned pointer. */
  22         const uintptr_t s_int = (uintptr_t) s;
  23         const uint32_t *p = (const uint32_t *)(s_int & -4);
  24
  25         /* Read the first word, but force bytes before the string to be nonzero.
  26          * This expression works because we know shift counts are taken mod 32.
  27          */
  28         uint32_t v = *p | ((1 << (s_int << 3)) - 1);
  29
  30         uint32_t bits;
  31         while ((bits = __insn_seqb(v, 0)) == 0)
  32                 v = *++p;
  33
  34         return ((const char *)p) + (__insn_ctz(bits) >> 3) - s;
  35 }
  36 EXPORT_SYMBOL(strlen);