1/*	$OpenBSD: strstr.c,v 1.9 2020/04/16 12:37:52 claudio Exp $ */
2
3/*
4 * Copyright (c) 2005-2018 Rich Felker
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
26#include <string.h>
27#include <stdint.h>
28
29static char *
30twobyte_strstr(const unsigned char *h, const unsigned char *n)
31{
32	uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
33	for (h++; *h && hw != nw; hw = hw<<8 | *++h);
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 = n[0]<<24 | n[1]<<16 | n[2]<<8;
41	uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
42	for (h+=2; *h && hw != nw; hw = (hw|*++h)<<8);
43	return *h ? (char *)h-2 : 0;
44}
45
46static char *
47fourbyte_strstr(const unsigned char *h, const unsigned char *n)
48{
49	uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
50	uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
51	for (h+=3; *h && hw != nw; hw = hw<<8 | *++h);
52	return *h ? (char *)h-3 : 0;
53}
54
55#define MAX(a,b) ((a)>(b)?(a):(b))
56#define MIN(a,b) ((a)<(b)?(a):(b))
57
58#define BITOP(a,b,op) \
59 ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
60
61/*
62 * Maxime Crochemore and Dominique Perrin, Two-way string-matching,
63 * Journal of the ACM, 38(3):651-675, July 1991.
64 */
65static char *
66twoway_strstr(const unsigned char *h, const unsigned char *n)
67{
68	const unsigned char *z;
69	size_t l, ip, jp, k, p, ms, p0, mem, mem0;
70	size_t byteset[32 / sizeof(size_t)] = { 0 };
71	size_t shift[256];
72
73	/* Computing length of needle and fill shift table */
74	for (l=0; n[l] && h[l]; l++)
75		BITOP(byteset, n[l], |=), shift[n[l]] = l+1;
76	if (n[l]) return 0; /* hit the end of h */
77
78	/* Compute maximal suffix */
79	ip = -1; jp = 0; k = p = 1;
80	while (jp+k<l) {
81		if (n[ip+k] == n[jp+k]) {
82			if (k == p) {
83				jp += p;
84				k = 1;
85			} else k++;
86		} else if (n[ip+k] > n[jp+k]) {
87			jp += k;
88			k = 1;
89			p = jp - ip;
90		} else {
91			ip = jp++;
92			k = p = 1;
93		}
94	}
95	ms = ip;
96	p0 = p;
97
98	/* And with the opposite comparison */
99	ip = -1; jp = 0; k = p = 1;
100	while (jp+k<l) {
101		if (n[ip+k] == n[jp+k]) {
102			if (k == p) {
103				jp += p;
104				k = 1;
105			} else k++;
106		} else if (n[ip+k] < n[jp+k]) {
107			jp += k;
108			k = 1;
109			p = jp - ip;
110		} else {
111			ip = jp++;
112			k = p = 1;
113		}
114	}
115	if (ip+1 > ms+1) ms = ip;
116	else p = p0;
117
118	/* Periodic needle? */
119	if (memcmp(n, n+p, ms+1)) {
120		mem0 = 0;
121		p = MAX(ms, l-ms-1) + 1;
122	} else mem0 = l-p;
123	mem = 0;
124
125	/* Initialize incremental end-of-haystack pointer */
126	z = h;
127
128	/* Search loop */
129	for (;;) {
130		/* Update incremental end-of-haystack pointer */
131		if (z-h < l) {
132			/* Fast estimate for MIN(l,63) */
133			size_t grow = l | 63;
134			const unsigned char *z2 = memchr(z, 0, grow);
135			if (z2) {
136				z = z2;
137				if (z-h < l) return 0;
138			} else z += grow;
139		}
140
141		/* Check last byte first; advance by shift on mismatch */
142		if (BITOP(byteset, h[l-1], &)) {
143			k = l-shift[h[l-1]];
144			if (k) {
145				if (k < mem) k = mem;
146				h += k;
147				mem = 0;
148				continue;
149			}
150		} else {
151			h += l;
152			mem = 0;
153			continue;
154		}
155
156		/* Compare right half */
157		for (k=MAX(ms+1,mem); n[k] && n[k] == h[k]; k++);
158		if (n[k]) {
159			h += k-ms;
160			mem = 0;
161			continue;
162		}
163		/* Compare left half */
164		for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
165		if (k <= mem) return (char *)h;
166		h += p;
167		mem = mem0;
168	}
169}
170
171char *
172strstr(const char *h, const char *n)
173{
174	/* Return immediately on empty needle */
175	if (!n[0]) return (char *)h;
176
177	/* Use faster algorithms for short needles */
178	h = strchr(h, *n);
179	if (!h || !n[1]) return (char *)h;
180	if (!h[1]) return 0;
181	if (!n[2]) return twobyte_strstr((void *)h, (void *)n);
182	if (!h[2]) return 0;
183	if (!n[3]) return threebyte_strstr((void *)h, (void *)n);
184	if (!h[3]) return 0;
185	if (!n[4]) return fourbyte_strstr((void *)h, (void *)n);
186
187	return twoway_strstr((void *)h, (void *)n);
188}
189DEF_STRONG(strstr);
190