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