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 <sys/cdefs.h> 26 __FBSDID("$FreeBSD$"); 27 28 #include <stdint.h> 29 #include <string.h> 30 31 static char * 32 twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) 33 { 34 uint16_t nw = n[0] << 8 | n[1], hw = h[0] << 8 | h[1]; 35 for (h += 2, k -= 2; k; k--, hw = hw << 8 | *h++) 36 if (hw == nw) 37 return (char *)h - 2; 38 return hw == nw ? (char *)h - 2 : 0; 39 } 40 41 static char * 42 threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) 43 { 44 uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8; 45 uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8; 46 for (h += 3, k -= 3; k; k--, hw = (hw | *h++) << 8) 47 if (hw == nw) 48 return (char *)h - 3; 49 return hw == nw ? (char *)h - 3 : 0; 50 } 51 52 static char * 53 fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) 54 { 55 uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3]; 56 uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3]; 57 for (h += 4, k -= 4; k; k--, hw = hw << 8 | *h++) 58 if (hw == nw) 59 return (char *)h - 4; 60 return hw == nw ? (char *)h - 4 : 0; 61 } 62 63 #define MAX(a, b) ((a) > (b) ? (a) : (b)) 64 #define MIN(a, b) ((a) < (b) ? (a) : (b)) 65 66 #define BITOP(a, b, op) \ 67 ((a)[(size_t)(b) / (8 * sizeof *(a))] op \ 68 (size_t)1 << ((size_t)(b) % (8 * sizeof *(a)))) 69 70 /* 71 * Two Way string search algorithm, with a bad shift table applied to the last 72 * byte of the window. A bit array marks which entries in the shift table are 73 * initialized to avoid fully initializing a 1kb/2kb table. 74 * 75 * Reference: CROCHEMORE M., PERRIN D., 1991, Two-way string-matching, 76 * Journal of the ACM 38(3):651-675 77 */ 78 static char * 79 twoway_memmem(const unsigned char *h, const unsigned char *z, 80 const unsigned char *n, size_t l) 81 { 82 size_t i, ip, jp, k, p, ms, p0, mem, mem0; 83 size_t byteset[32 / sizeof(size_t)] = { 0 }; 84 size_t shift[256]; 85 86 /* Computing length of needle and fill shift table */ 87 for (i = 0; i < l; i++) 88 BITOP(byteset, n[i], |=), shift[n[i]] = i + 1; 89 90 /* Compute maximal suffix */ 91 ip = -1; 92 jp = 0; 93 k = p = 1; 94 while (jp + k < l) { 95 if (n[ip + k] == n[jp + k]) { 96 if (k == p) { 97 jp += p; 98 k = 1; 99 } else 100 k++; 101 } else if (n[ip + k] > n[jp + k]) { 102 jp += k; 103 k = 1; 104 p = jp - ip; 105 } else { 106 ip = jp++; 107 k = p = 1; 108 } 109 } 110 ms = ip; 111 p0 = p; 112 113 /* And with the opposite comparison */ 114 ip = -1; 115 jp = 0; 116 k = p = 1; 117 while (jp + k < l) { 118 if (n[ip + k] == n[jp + k]) { 119 if (k == p) { 120 jp += p; 121 k = 1; 122 } else 123 k++; 124 } else if (n[ip + k] < n[jp + k]) { 125 jp += k; 126 k = 1; 127 p = jp - ip; 128 } else { 129 ip = jp++; 130 k = p = 1; 131 } 132 } 133 if (ip + 1 > ms + 1) 134 ms = ip; 135 else 136 p = p0; 137 138 /* Periodic needle? */ 139 if (memcmp(n, n + p, ms + 1)) { 140 mem0 = 0; 141 p = MAX(ms, l - ms - 1) + 1; 142 } else 143 mem0 = l - p; 144 mem = 0; 145 146 /* Search loop */ 147 for (;;) { 148 /* If remainder of haystack is shorter than needle, done */ 149 if (z - h < l) 150 return 0; 151 152 /* Check last byte first; advance by shift on mismatch */ 153 if (BITOP(byteset, h[l - 1], &)) { 154 k = l - shift[h[l - 1]]; 155 if (k) { 156 if (k < mem) 157 k = mem; 158 h += k; 159 mem = 0; 160 continue; 161 } 162 } else { 163 h += l; 164 mem = 0; 165 continue; 166 } 167 168 /* Compare right half */ 169 for (k = MAX(ms + 1, mem); k < l && n[k] == h[k]; k++) 170 ; 171 if (k < l) { 172 h += k - ms; 173 mem = 0; 174 continue; 175 } 176 /* Compare left half */ 177 for (k = ms + 1; k > mem && n[k - 1] == h[k - 1]; k--) 178 ; 179 if (k <= mem) 180 return (char *)h; 181 h += p; 182 mem = mem0; 183 } 184 } 185 186 void * 187 memmem(const void *h0, size_t k, const void *n0, size_t l) 188 { 189 const unsigned char *h = h0, *n = n0; 190 191 /* Return immediately on empty needle */ 192 if (!l) 193 return (void *)h; 194 195 /* Return immediately when needle is longer than haystack */ 196 if (k < l) 197 return 0; 198 199 /* Use faster algorithms for short needles */ 200 h = memchr(h0, *n, k); 201 if (!h || l == 1) 202 return (void *)h; 203 k -= h - (const unsigned char *)h0; 204 if (k < l) 205 return 0; 206 if (l == 2) 207 return twobyte_memmem(h, k, n); 208 if (l == 3) 209 return threebyte_memmem(h, k, n); 210 if (l == 4) 211 return fourbyte_memmem(h, k, n); 212 213 return twoway_memmem(h, h + k, n, l); 214 } 215