arch/tile/lib/strlen_64.c

   1 /*
   2  * Copyright 2011 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 #undef strlen
  20
  21 size_t strlen(const char *s)
  22 {
  23         /* Get an aligned pointer. */
  24         const uintptr_t s_int = (uintptr_t) s;
  25         const uint64_t *p = (const uint64_t *)(s_int & -8);
  26
  27         /* Read the first word, but force bytes before the string to be nonzero.
  28          * This expression works because we know shift counts are taken mod 64.
  29          */
  30         uint64_t v = *p | ((1ULL << (s_int << 3)) - 1);
  31
  32         uint64_t bits;
  33         while ((bits = __insn_v1cmpeqi(v, 0)) == 0)
  34                 v = *++p;
  35
  36         return ((const char *)p) + (__insn_ctz(bits) >> 3) - s;
  37 }
  38 EXPORT_SYMBOL(strlen);