1/*
2** Copyright 2001, Travis Geiselbrecht. All rights reserved.
3** Distributed under the terms of the NewOS License.
4*/
5
6#include <string.h>
7#include <SupportDefs.h>
8
9
10/* From Bit twiddling hacks:
11	http://graphics.stanford.edu/~seander/bithacks.html */
12#define LACKS_ZERO_BYTE(value) \
13	(((value - 0x01010101) & ~value & 0x80808080) == 0)
14
15
16size_t
17strnlen(const char* string, size_t count)
18{
19	size_t length = 0;
20	/* Align access for four byte reads */
21	for (; (((addr_t)string + length) & 3) != 0; length++) {
22		if (length == count || string[length] == '\0')
23			return length;
24	}
25
26	/* Check four bytes for zero char */
27	const uint32* kMaxScanPosition = (uint32*)(string + count - 4);
28	uint32* valuePointer = (uint32*)(string + length);
29	for (; valuePointer <= kMaxScanPosition && LACKS_ZERO_BYTE(*valuePointer);
30		valuePointer++)
31		;
32
33	/* Find the exact length */
34	for (length = ((char*)valuePointer) - string; length < count
35		&& string[length] != '\0'; length++)
36		;
37
38	return length;
39}
40