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
19void *memchr(const void *s, int c, size_t n)
20{
21	const uint32_t *last_word_ptr;
22	const uint32_t *p;
23	const char *last_byte_ptr;
24	uintptr_t s_int;
25	uint32_t goal, before_mask, v, bits;
26	char *ret;
27
28	if (__builtin_expect(n == 0, 0)) {
29		/* Don't dereference any memory if the array is empty. */
30		return NULL;
31	}
32
33	/* Get an aligned pointer. */
34	s_int = (uintptr_t) s;
35	p = (const uint32_t *)(s_int & -4);
36
37	/* Create four copies of the byte for which we are looking. */
38	goal = 0x01010101 * (uint8_t) c;
39
40	/* Read the first word, but munge it so that bytes before the array
41	 * will not match goal.
42	 *
43	 * Note that this shift count expression works because we know
44	 * shift counts are taken mod 32.
45	 */
46	before_mask = (1 << (s_int << 3)) - 1;
47	v = (*p | before_mask) ^ (goal & before_mask);
48
49	/* Compute the address of the last byte. */
50	last_byte_ptr = (const char *)s + n - 1;
51
52	/* Compute the address of the word containing the last byte. */
53	last_word_ptr = (const uint32_t *)((uintptr_t) last_byte_ptr & -4);
54
55	while ((bits = __insn_seqb(v, goal)) == 0) {
56		if (__builtin_expect(p == last_word_ptr, 0)) {
57			/* We already read the last word in the array,
58			 * so give up.
59			 */
60			return NULL;
61		}
62		v = *++p;
63	}
64
65	/* We found a match, but it might be in a byte past the end
66	 * of the array.
67	 */
68	ret = ((char *)p) + (__insn_ctz(bits) >> 3);
69	return (ret <= last_byte_ptr) ? ret : NULL;
70}
71EXPORT_SYMBOL(memchr);
72