1/*-
2 * SPDX-License-Identifier: MIT
3 *
4 * Copyright (c) 2005-2014 Rich Felker, et al.
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining
7 * a copy of this software and associated documentation files (the
8 * "Software"), to deal in the Software without restriction, including
9 * without limitation the rights to use, copy, modify, merge, publish,
10 * distribute, sublicense, and/or sell copies of the Software, and to
11 * permit persons to whom the Software is furnished to do so, subject to
12 * the following conditions:
13 *
14 * The above copyright notice and this permission notice shall be
15 * included in all copies or substantial portions of the Software.
16 *
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
18 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
19 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
20 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
21 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
22 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
23 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
24 */
25#include <sys/cdefs.h>
26__FBSDID("$FreeBSD$");
27
28#include <stdint.h>
29#include <string.h>
30
31static char *
32twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
33{
34	uint16_t nw = n[0] << 8 | n[1], hw = h[0] << 8 | h[1];
35	for (h += 2, k -= 2; k; k--, hw = hw << 8 | *h++)
36		if (hw == nw)
37			return (char *)h - 2;
38	return hw == nw ? (char *)h - 2 : 0;
39}
40
41static char *
42threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
43{
44	uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8;
45	uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8;
46	for (h += 3, k -= 3; k; k--, hw = (hw | *h++) << 8)
47		if (hw == nw)
48			return (char *)h - 3;
49	return hw == nw ? (char *)h - 3 : 0;
50}
51
52static char *
53fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
54{
55	uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3];
56	uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3];
57	for (h += 4, k -= 4; k; k--, hw = hw << 8 | *h++)
58		if (hw == nw)
59			return (char *)h - 4;
60	return hw == nw ? (char *)h - 4 : 0;
61}
62
63#define MAX(a, b) ((a) > (b) ? (a) : (b))
64#define MIN(a, b) ((a) < (b) ? (a) : (b))
65
66#define BITOP(a, b, op) \
67	((a)[(size_t)(b) / (8 * sizeof *(a))] op \
68	    (size_t)1 << ((size_t)(b) % (8 * sizeof *(a))))
69
70/*
71 * Two Way string search algorithm, with a bad shift table applied to the last
72 * byte of the window. A bit array marks which entries in the shift table are
73 * initialized to avoid fully initializing a 1kb/2kb table.
74 *
75 * Reference: CROCHEMORE M., PERRIN D., 1991, Two-way string-matching,
76 * Journal of the ACM 38(3):651-675
77 */
78static char *
79twoway_memmem(const unsigned char *h, const unsigned char *z,
80    const unsigned char *n, size_t l)
81{
82	size_t i, ip, jp, k, p, ms, p0, mem, mem0;
83	size_t byteset[32 / sizeof(size_t)] = { 0 };
84	size_t shift[256];
85
86	/* Computing length of needle and fill shift table */
87	for (i = 0; i < l; i++)
88		BITOP(byteset, n[i], |=), shift[n[i]] = i + 1;
89
90	/* Compute maximal suffix */
91	ip = -1;
92	jp = 0;
93	k = p = 1;
94	while (jp + k < l) {
95		if (n[ip + k] == n[jp + k]) {
96			if (k == p) {
97				jp += p;
98				k = 1;
99			} else
100				k++;
101		} else if (n[ip + k] > n[jp + k]) {
102			jp += k;
103			k = 1;
104			p = jp - ip;
105		} else {
106			ip = jp++;
107			k = p = 1;
108		}
109	}
110	ms = ip;
111	p0 = p;
112
113	/* And with the opposite comparison */
114	ip = -1;
115	jp = 0;
116	k = p = 1;
117	while (jp + k < l) {
118		if (n[ip + k] == n[jp + k]) {
119			if (k == p) {
120				jp += p;
121				k = 1;
122			} else
123				k++;
124		} else if (n[ip + k] < n[jp + k]) {
125			jp += k;
126			k = 1;
127			p = jp - ip;
128		} else {
129			ip = jp++;
130			k = p = 1;
131		}
132	}
133	if (ip + 1 > ms + 1)
134		ms = ip;
135	else
136		p = p0;
137
138	/* Periodic needle? */
139	if (memcmp(n, n + p, ms + 1)) {
140		mem0 = 0;
141		p = MAX(ms, l - ms - 1) + 1;
142	} else
143		mem0 = l - p;
144	mem = 0;
145
146	/* Search loop */
147	for (;;) {
148		/* If remainder of haystack is shorter than needle, done */
149		if (z - h < l)
150			return 0;
151
152		/* Check last byte first; advance by shift on mismatch */
153		if (BITOP(byteset, h[l - 1], &)) {
154			k = l - shift[h[l - 1]];
155			if (k) {
156				if (k < mem)
157					k = mem;
158				h += k;
159				mem = 0;
160				continue;
161			}
162		} else {
163			h += l;
164			mem = 0;
165			continue;
166		}
167
168		/* Compare right half */
169		for (k = MAX(ms + 1, mem); k < l && n[k] == h[k]; k++)
170			;
171		if (k < l) {
172			h += k - ms;
173			mem = 0;
174			continue;
175		}
176		/* Compare left half */
177		for (k = ms + 1; k > mem && n[k - 1] == h[k - 1]; k--)
178			;
179		if (k <= mem)
180			return (char *)h;
181		h += p;
182		mem = mem0;
183	}
184}
185
186void *
187memmem(const void *h0, size_t k, const void *n0, size_t l)
188{
189	const unsigned char *h = h0, *n = n0;
190
191	/* Return immediately on empty needle */
192	if (!l)
193		return (void *)h;
194
195	/* Return immediately when needle is longer than haystack */
196	if (k < l)
197		return 0;
198
199	/* Use faster algorithms for short needles */
200	h = memchr(h0, *n, k);
201	if (!h || l == 1)
202		return (void *)h;
203	k -= h - (const unsigned char *)h0;
204	if (k < l)
205		return 0;
206	if (l == 2)
207		return twobyte_memmem(h, k, n);
208	if (l == 3)
209		return threebyte_memmem(h, k, n);
210	if (l == 4)
211		return fourbyte_memmem(h, k, n);
212
213	return twoway_memmem(h, h + k, n, l);
214}
215