LXR linux/arch/tile/lib/strnlen

   1/*
   2 * Copyright 2013 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 strnlen(const char *s, size_t count)
  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        size_t bytes_read = sizeof(*p) - (s_int & (sizeof(*p) - 1));
  25        size_t len;
  26        uint32_t v, bits;
  27
  28        /* Avoid page fault risk by not reading any bytes when count is 0. */
  29        if (count == 0)
  30                return 0;
  31
  32        /* Read first word, but force bytes before the string to be nonzero. */
  33        v = *p | ((1 << ((s_int << 3) & 31)) - 1);
  34
  35        while ((bits = __insn_seqb(v, 0)) == 0) {
  36                if (bytes_read >= count) {
  37                        /* Read COUNT bytes and didn't find the terminator. */
  38                        return count;
  39                }
  40                v = *++p;
  41                bytes_read += sizeof(v);
  42        }
  43
  44        len = ((const char *) p) + (__insn_ctz(bits) >> 3) - s;
  45        return (len < count ? len : count);
  46}
  47EXPORT_SYMBOL(strnlen);
  48