LXR linux/arch/tile/lib/strlen

   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
  19size_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}
  36EXPORT_SYMBOL(strlen);
  37