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