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 /* OPENBSD ORIGINAL: lib/libc/string/memmem.c */
27
28 #include "includes.h"
29
30 #ifndef HAVE_MEMMEM
31
32 #include <string.h>
33 #ifdef HAVE_STDINT_H
34 #include <stdint.h>
35 #endif
36
37 static char *
twobyte_memmem(const unsigned char * h,size_t k,const unsigned char * n)38 twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
39 {
40 uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
41 for (h+=2, k-=2; k; k--, hw = hw<<8 | *h++)
42 if (hw == nw) return (char *)h-2;
43 return hw == nw ? (char *)h-2 : 0;
44 }
45
46 static char *
threebyte_memmem(const unsigned char * h,size_t k,const unsigned char * n)47 threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
48 {
49 uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
50 uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
51 for (h+=3, k-=3; k; k--, hw = (hw|*h++)<<8)
52 if (hw == nw) return (char *)h-3;
53 return hw == nw ? (char *)h-3 : 0;
54 }
55
56 static char *
fourbyte_memmem(const unsigned char * h,size_t k,const unsigned char * n)57 fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
58 {
59 uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
60 uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
61 for (h+=4, k-=4; k; k--, hw = hw<<8 | *h++)
62 if (hw == nw) return (char *)h-4;
63 return hw == nw ? (char *)h-4 : 0;
64 }
65
66 #if 0
67 /* In -portable, defines.h ensures that these are already defined. */
68 #define MAX(a,b) ((a)>(b)?(a):(b))
69 #define MIN(a,b) ((a)<(b)?(a):(b))
70 #endif
71
72 #define BITOP(a,b,op) \
73 ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
74
75 /*
76 * Maxime Crochemore and Dominique Perrin, Two-way string-matching,
77 * Journal of the ACM, 38(3):651-675, July 1991.
78 */
79 static char *
twoway_memmem(const unsigned char * h,const unsigned char * z,const unsigned char * n,size_t l)80 twoway_memmem(const unsigned char *h, const unsigned char *z,
81 const unsigned char *n, size_t l)
82 {
83 size_t i, ip, jp, k, p, ms, p0, mem, mem0;
84 size_t byteset[32 / sizeof(size_t)] = { 0 };
85 size_t shift[256];
86
87 /* Computing length of needle and fill shift table */
88 for (i=0; i<l; i++)
89 BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
90
91 /* Compute maximal suffix */
92 ip = -1; jp = 0; k = p = 1;
93 while (jp+k<l) {
94 if (n[ip+k] == n[jp+k]) {
95 if (k == p) {
96 jp += p;
97 k = 1;
98 } else k++;
99 } else if (n[ip+k] > n[jp+k]) {
100 jp += k;
101 k = 1;
102 p = jp - ip;
103 } else {
104 ip = jp++;
105 k = p = 1;
106 }
107 }
108 ms = ip;
109 p0 = p;
110
111 /* And with the opposite comparison */
112 ip = -1; jp = 0; 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 k++;
119 } else if (n[ip+k] < n[jp+k]) {
120 jp += k;
121 k = 1;
122 p = jp - ip;
123 } else {
124 ip = jp++;
125 k = p = 1;
126 }
127 }
128 if (ip+1 > ms+1) ms = ip;
129 else p = p0;
130
131 /* Periodic needle? */
132 if (memcmp(n, n+p, ms+1)) {
133 mem0 = 0;
134 p = MAX(ms, l-ms-1) + 1;
135 } else mem0 = l-p;
136 mem = 0;
137
138 /* Search loop */
139 for (;;) {
140 /* If remainder of haystack is shorter than needle, done */
141 if (z-h < l) return 0;
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); k<l && n[k] == h[k]; k++);
160 if (k < l) {
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
173 void *
memmem(const void * h0,size_t k,const void * n0,size_t l)174 memmem(const void *h0, size_t k, const void *n0, size_t l)
175 {
176 const unsigned char *h = h0, *n = n0;
177
178 /* Return immediately on empty needle */
179 if (!l) return (void *)h;
180
181 /* Return immediately when needle is longer than haystack */
182 if (k<l) return 0;
183
184 /* Use faster algorithms for short needles */
185 h = memchr(h0, *n, k);
186 if (!h || l==1) return (void *)h;
187 k -= h - (const unsigned char *)h0;
188 if (k<l) return 0;
189 if (l==2) return twobyte_memmem(h, k, n);
190 if (l==3) return threebyte_memmem(h, k, n);
191 if (l==4) return fourbyte_memmem(h, k, n);
192
193 return twoway_memmem(h, h+k, n, l);
194 }
195 DEF_WEAK(memmem);
196 #endif /* HAVE_MEMMEM */
197