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