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_strstr(const unsigned char *h, const unsigned char *n) 30 { 31 uint16_t nw = n[0] << 8 | n[1], hw = h[0] << 8 | h[1]; 32 for (h++; *h && hw != nw; hw = hw << 8 | *++h) 33 ; 34 return *h ? (char *)h - 1 : 0; 35 } 36 37 static char * 38 threebyte_strstr(const unsigned char *h, const unsigned char *n) 39 { 40 uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8; 41 uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8; 42 for (h += 2; *h && hw != nw; hw = (hw | *++h) << 8) 43 ; 44 return *h ? (char *)h - 2 : 0; 45 } 46 47 static char * 48 fourbyte_strstr(const unsigned char *h, const unsigned char *n) 49 { 50 uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3]; 51 uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3]; 52 for (h += 3; *h && hw != nw; hw = hw << 8 | *++h) 53 ; 54 return *h ? (char *)h - 3 : 0; 55 } 56 57 #define MAX(a, b) ((a) > (b) ? (a) : (b)) 58 #define MIN(a, b) ((a) < (b) ? (a) : (b)) 59 60 #define BITOP(a, b, op) \ 61 ((a)[(size_t)(b) / (8 * sizeof *(a))] op \ 62 (size_t)1 << ((size_t)(b) % (8 * sizeof *(a)))) 63 64 /* 65 * Two Way string search algorithm, with a bad shift table applied to the last 66 * byte of the window. A bit array marks which entries in the shift table are 67 * initialized to avoid fully initializing a 1kb/2kb table. 68 * 69 * Reference: CROCHEMORE M., PERRIN D., 1991, Two-way string-matching, 70 * Journal of the ACM 38(3):651-675 71 */ 72 static char * 73 twoway_strstr(const unsigned char *h, const unsigned char *n) 74 { 75 const unsigned char *z; 76 size_t l, ip, jp, k, p, ms, p0, mem, mem0; 77 size_t byteset[32 / sizeof(size_t)] = { 0 }; 78 size_t shift[256]; 79 80 /* Computing length of needle and fill shift table */ 81 for (l = 0; n[l] && h[l]; l++) 82 BITOP(byteset, n[l], |=), shift[n[l]] = l + 1; 83 if (n[l]) 84 return 0; /* hit the end of h */ 85 86 /* Compute maximal suffix */ 87 ip = -1; 88 jp = 0; 89 k = p = 1; 90 while (jp + k < l) { 91 if (n[ip + k] == n[jp + k]) { 92 if (k == p) { 93 jp += p; 94 k = 1; 95 } else 96 k++; 97 } else if (n[ip + k] > n[jp + k]) { 98 jp += k; 99 k = 1; 100 p = jp - ip; 101 } else { 102 ip = jp++; 103 k = p = 1; 104 } 105 } 106 ms = ip; 107 p0 = p; 108 109 /* And with the opposite comparison */ 110 ip = -1; 111 jp = 0; 112 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 119 k++; 120 } else if (n[ip + k] < n[jp + k]) { 121 jp += k; 122 k = 1; 123 p = jp - ip; 124 } else { 125 ip = jp++; 126 k = p = 1; 127 } 128 } 129 if (ip + 1 > ms + 1) 130 ms = ip; 131 else 132 p = p0; 133 134 /* Periodic needle? */ 135 if (memcmp(n, n + p, ms + 1)) { 136 mem0 = 0; 137 p = MAX(ms, l - ms - 1) + 1; 138 } else 139 mem0 = l - p; 140 mem = 0; 141 142 /* Initialize incremental end-of-haystack pointer */ 143 z = h; 144 145 /* Search loop */ 146 for (;;) { 147 /* Update incremental end-of-haystack pointer */ 148 if (z - h < l) { 149 /* Fast estimate for MAX(l,63) */ 150 size_t grow = l | 63; 151 const unsigned char *z2 = memchr(z, 0, grow); 152 if (z2) { 153 z = z2; 154 if (z - h < l) 155 return 0; 156 } else 157 z += grow; 158 } 159 160 /* Check last byte first; advance by shift on mismatch */ 161 if (BITOP(byteset, h[l - 1], &)) { 162 k = l - shift[h[l - 1]]; 163 if (k) { 164 if (k < mem) 165 k = mem; 166 h += k; 167 mem = 0; 168 continue; 169 } 170 } else { 171 h += l; 172 mem = 0; 173 continue; 174 } 175 176 /* Compare right half */ 177 for (k = MAX(ms + 1, mem); n[k] && n[k] == h[k]; k++) 178 ; 179 if (n[k]) { 180 h += k - ms; 181 mem = 0; 182 continue; 183 } 184 /* Compare left half */ 185 for (k = ms + 1; k > mem && n[k - 1] == h[k - 1]; k--) 186 ; 187 if (k <= mem) 188 return (char *)h; 189 h += p; 190 mem = mem0; 191 } 192 } 193 194 char * 195 strstr(const char *h, const char *n) 196 { 197 /* Return immediately on empty needle */ 198 if (!n[0]) 199 return (char *)h; 200 201 /* Use faster algorithms for short needles */ 202 h = strchr(h, *n); 203 if (!h || !n[1]) 204 return (char *)h; 205 if (!h[1]) 206 return 0; 207 if (!n[2]) 208 return twobyte_strstr((void *)h, (void *)n); 209 if (!h[2]) 210 return 0; 211 if (!n[3]) 212 return threebyte_strstr((void *)h, (void *)n); 213 if (!h[3]) 214 return 0; 215 if (!n[4]) 216 return fourbyte_strstr((void *)h, (void *)n); 217 218 return twoway_strstr((void *)h, (void *)n); 219 } 220