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