arch/tile/lib/strnlen_32.c

   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
  19 size_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 }
  47 EXPORT_SYMBOL(strnlen);