1 /* $OpenBSD: memmem.c,v 1.5 2020/04/16 12:39:28 claudio Exp $ */
2
3 /*
4 * Copyright (c) 2005-2020 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
26 #include <string.h>
27 #include <stdint.h>
28
29 static char *
twobyte_memmem(const unsigned char * h,size_t k,const unsigned char * n)30 twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
31 {
32 uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
33 for (h+=2, k-=2; k; k--, hw = hw<<8 | *h++)
34 if (hw == nw) return (char *)h-2;
35 return hw == nw ? (char *)h-2 : 0;
36 }
37
38 static char *
threebyte_memmem(const unsigned char * h,size_t k,const unsigned char * n)39 threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
40 {
41 uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
42 uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
43 for (h+=3, k-=3; k; k--, hw = (hw|*h++)<<8)
44 if (hw == nw) return (char *)h-3;
45 return hw == nw ? (char *)h-3 : 0;
46 }
47
48 static char *
fourbyte_memmem(const unsigned char * h,size_t k,const unsigned char * n)49 fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
50 {
51 uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
52 uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
53 for (h+=4, k-=4; k; k--, hw = hw<<8 | *h++)
54 if (hw == nw) return (char *)h-4;
55 return hw == nw ? (char *)h-4 : 0;
56 }
57
58 #define MAX(a,b) ((a)>(b)?(a):(b))
59 #define MIN(a,b) ((a)<(b)?(a):(b))
60
61 #define BITOP(a,b,op) \
62 ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
63
64 /*
65 * Maxime Crochemore and Dominique Perrin, Two-way string-matching,
66 * Journal of the ACM, 38(3):651-675, July 1991.
67 */
68 static char *
twoway_memmem(const unsigned char * h,const unsigned char * z,const unsigned char * n,size_t l)69 twoway_memmem(const unsigned char *h, const unsigned char *z,
70 const unsigned char *n, size_t l)
71 {
72 size_t i, ip, jp, k, p, ms, p0, mem, mem0;
73 size_t byteset[32 / sizeof(size_t)] = { 0 };
74 size_t shift[256];
75
76 /* Computing length of needle and fill shift table */
77 for (i=0; i<l; i++)
78 BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
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 /* Search loop */
128 for (;;) {
129 /* If remainder of haystack is shorter than needle, done */
130 if (z-h < l) return 0;
131
132 /* Check last byte first; advance by shift on mismatch */
133 if (BITOP(byteset, h[l-1], &)) {
134 k = l-shift[h[l-1]];
135 if (k) {
136 if (k < mem) k = mem;
137 h += k;
138 mem = 0;
139 continue;
140 }
141 } else {
142 h += l;
143 mem = 0;
144 continue;
145 }
146
147 /* Compare right half */
148 for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++);
149 if (k < l) {
150 h += k-ms;
151 mem = 0;
152 continue;
153 }
154 /* Compare left half */
155 for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
156 if (k <= mem) return (char *)h;
157 h += p;
158 mem = mem0;
159 }
160 }
161
162 void *
memmem(const void * h0,size_t k,const void * n0,size_t l)163 memmem(const void *h0, size_t k, const void *n0, size_t l)
164 {
165 const unsigned char *h = h0, *n = n0;
166
167 /* Return immediately on empty needle */
168 if (!l) return (void *)h;
169
170 /* Return immediately when needle is longer than haystack */
171 if (k<l) return 0;
172
173 /* Use faster algorithms for short needles */
174 h = memchr(h0, *n, k);
175 if (!h || l==1) return (void *)h;
176 k -= h - (const unsigned char *)h0;
177 if (k<l) return 0;
178 if (l==2) return twobyte_memmem(h, k, n);
179 if (l==3) return threebyte_memmem(h, k, n);
180 if (l==4) return fourbyte_memmem(h, k, n);
181
182 return twoway_memmem(h, h+k, n, l);
183 }
184 DEF_WEAK(memmem);
185