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 <stdint.h>
26#include <string.h>
27
28static char *
29twobyte_strstr(const unsigned char *h, const unsigned char *n)
30{
31	uint16_t nw = n[0] << 8 | n[1], hw = h[0] << 8 | h[1];
32	for (h++; *h && hw != nw; hw = hw << 8 | *++h)
33		;
34	return *h ? (char *)h - 1 : 0;
35}
36
37static char *
38threebyte_strstr(const unsigned char *h, const unsigned char *n)
39{
40	uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8;
41	uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8;
42	for (h += 2; *h && hw != nw; hw = (hw | *++h) << 8)
43		;
44	return *h ? (char *)h - 2 : 0;
45}
46
47static char *
48fourbyte_strstr(const unsigned char *h, const unsigned char *n)
49{
50	uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3];
51	uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3];
52	for (h += 3; *h && hw != nw; hw = hw << 8 | *++h)
53		;
54	return *h ? (char *)h - 3 : 0;
55}
56
57#define MAX(a, b) ((a) > (b) ? (a) : (b))
58#define MIN(a, b) ((a) < (b) ? (a) : (b))
59
60#define BITOP(a, b, op) \
61	((a)[(size_t)(b) / (8 * sizeof *(a))] op \
62	    (size_t)1 << ((size_t)(b) % (8 * sizeof *(a))))
63
64/*
65 * Two Way string search algorithm, with a bad shift table applied to the last
66 * byte of the window. A bit array marks which entries in the shift table are
67 * initialized to avoid fully initializing a 1kb/2kb table.
68 *
69 * Reference: CROCHEMORE M., PERRIN D., 1991, Two-way string-matching,
70 * Journal of the ACM 38(3):651-675
71 */
72static char *
73twoway_strstr(const unsigned char *h, const unsigned char *n)
74{
75	const unsigned char *z;
76	size_t l, ip, jp, k, p, ms, p0, mem, mem0;
77	size_t byteset[32 / sizeof(size_t)] = { 0 };
78	size_t shift[256];
79
80	/* Computing length of needle and fill shift table */
81	for (l = 0; n[l] && h[l]; l++)
82		BITOP(byteset, n[l], |=), shift[n[l]] = l + 1;
83	if (n[l])
84		return 0; /* hit the end of h */
85
86	/* Compute maximal suffix */
87	ip = -1;
88	jp = 0;
89	k = p = 1;
90	while (jp + k < l) {
91		if (n[ip + k] == n[jp + k]) {
92			if (k == p) {
93				jp += p;
94				k = 1;
95			} else
96				k++;
97		} else if (n[ip + k] > n[jp + k]) {
98			jp += k;
99			k = 1;
100			p = jp - ip;
101		} else {
102			ip = jp++;
103			k = p = 1;
104		}
105	}
106	ms = ip;
107	p0 = p;
108
109	/* And with the opposite comparison */
110	ip = -1;
111	jp = 0;
112	k = p = 1;
113	while (jp + k < l) {
114		if (n[ip + k] == n[jp + k]) {
115			if (k == p) {
116				jp += p;
117				k = 1;
118			} else
119				k++;
120		} else if (n[ip + k] < n[jp + k]) {
121			jp += k;
122			k = 1;
123			p = jp - ip;
124		} else {
125			ip = jp++;
126			k = p = 1;
127		}
128	}
129	if (ip + 1 > ms + 1)
130		ms = ip;
131	else
132		p = p0;
133
134	/* Periodic needle? */
135	if (memcmp(n, n + p, ms + 1)) {
136		mem0 = 0;
137		p = MAX(ms, l - ms - 1) + 1;
138	} else
139		mem0 = l - p;
140	mem = 0;
141
142	/* Initialize incremental end-of-haystack pointer */
143	z = h;
144
145	/* Search loop */
146	for (;;) {
147		/* Update incremental end-of-haystack pointer */
148		if (z - h < l) {
149			/* Fast estimate for MAX(l,63) */
150			size_t grow = l | 63;
151			const unsigned char *z2 = memchr(z, 0, grow);
152			if (z2) {
153				z = z2;
154				if (z - h < l)
155					return 0;
156			} else
157				z += grow;
158		}
159
160		/* Check last byte first; advance by shift on mismatch */
161		if (BITOP(byteset, h[l - 1], &)) {
162			k = l - shift[h[l - 1]];
163			if (k) {
164				if (k < mem)
165					k = mem;
166				h += k;
167				mem = 0;
168				continue;
169			}
170		} else {
171			h += l;
172			mem = 0;
173			continue;
174		}
175
176		/* Compare right half */
177		for (k = MAX(ms + 1, mem); n[k] && n[k] == h[k]; k++)
178			;
179		if (n[k]) {
180			h += k - ms;
181			mem = 0;
182			continue;
183		}
184		/* Compare left half */
185		for (k = ms + 1; k > mem && n[k - 1] == h[k - 1]; k--)
186			;
187		if (k <= mem)
188			return (char *)h;
189		h += p;
190		mem = mem0;
191	}
192}
193
194char *
195strstr(const char *h, const char *n)
196{
197	/* Return immediately on empty needle */
198	if (!n[0])
199		return (char *)h;
200
201	/* Use faster algorithms for short needles */
202	h = strchr(h, *n);
203	if (!h || !n[1])
204		return (char *)h;
205	if (!h[1])
206		return 0;
207	if (!n[2])
208		return twobyte_strstr((void *)h, (void *)n);
209	if (!h[2])
210		return 0;
211	if (!n[3])
212		return threebyte_strstr((void *)h, (void *)n);
213	if (!h[3])
214		return 0;
215	if (!n[4])
216		return fourbyte_strstr((void *)h, (void *)n);
217
218	return twoway_strstr((void *)h, (void *)n);
219}
220