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_strstr(const unsigned char *h, const unsigned char *n) 31 { 32 uint16_t nw = n[0] << 8 | n[1], hw = h[0] << 8 | h[1]; 33 for (h++; *h && hw != nw; hw = hw << 8 | *++h) 34 ; 35 return *h ? (char *)h - 1 : 0; 36 } 37 38 static char * 39 threebyte_strstr(const unsigned char *h, 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 += 2; *h && hw != nw; hw = (hw | *++h) << 8) 44 ; 45 return *h ? (char *)h - 2 : 0; 46 } 47 48 static char * 49 fourbyte_strstr(const unsigned char *h, const unsigned char *n) 50 { 51 uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3]; 52 uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3]; 53 for (h += 3; *h && hw != nw; hw = hw << 8 | *++h) 54 ; 55 return *h ? (char *)h - 3 : 0; 56 } 57 58 #define MAX(a, b) ((a) > (b) ? (a) : (b)) 59 #define MIN(a, b) ((a) < (b) ? (a) : (b)) 60 61 #define BITOP(a, b, op) \ 62 ((a)[(size_t)(b) / (8 * sizeof *(a))] op \ 63 (size_t)1 << ((size_t)(b) % (8 * sizeof *(a)))) 64 65 /* 66 * Two Way string search algorithm, with a bad shift table applied to the last 67 * byte of the window. A bit array marks which entries in the shift table are 68 * initialized to avoid fully initializing a 1kb/2kb table. 69 * 70 * Reference: CROCHEMORE M., PERRIN D., 1991, Two-way string-matching, 71 * Journal of the ACM 38(3):651-675 72 */ 73 static char * 74 twoway_strstr(const unsigned char *h, const unsigned char *n) 75 { 76 const unsigned char *z; 77 size_t l, ip, jp, k, p, ms, p0, mem, mem0; 78 size_t byteset[32 / sizeof(size_t)] = { 0 }; 79 size_t shift[256]; 80 81 /* Computing length of needle and fill shift table */ 82 for (l = 0; n[l] && h[l]; l++) 83 BITOP(byteset, n[l], |=), shift[n[l]] = l + 1; 84 if (n[l]) 85 return 0; /* hit the end of h */ 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 /* Initialize incremental end-of-haystack pointer */ 144 z = h; 145 146 /* Search loop */ 147 for (;;) { 148 /* Update incremental end-of-haystack pointer */ 149 if (z - h < l) { 150 /* Fast estimate for MAX(l,63) */ 151 size_t grow = l | 63; 152 const unsigned char *z2 = memchr(z, 0, grow); 153 if (z2) { 154 z = z2; 155 if (z - h < l) 156 return 0; 157 } else 158 z += grow; 159 } 160 161 /* Check last byte first; advance by shift on mismatch */ 162 if (BITOP(byteset, h[l - 1], &)) { 163 k = l - shift[h[l - 1]]; 164 if (k) { 165 if (k < mem) 166 k = mem; 167 h += k; 168 mem = 0; 169 continue; 170 } 171 } else { 172 h += l; 173 mem = 0; 174 continue; 175 } 176 177 /* Compare right half */ 178 for (k = MAX(ms + 1, mem); n[k] && n[k] == h[k]; k++) 179 ; 180 if (n[k]) { 181 h += k - ms; 182 mem = 0; 183 continue; 184 } 185 /* Compare left half */ 186 for (k = ms + 1; k > mem && n[k - 1] == h[k - 1]; k--) 187 ; 188 if (k <= mem) 189 return (char *)h; 190 h += p; 191 mem = mem0; 192 } 193 } 194 195 char * 196 strstr(const char *h, const char *n) 197 { 198 /* Return immediately on empty needle */ 199 if (!n[0]) 200 return (char *)h; 201 202 /* Use faster algorithms for short needles */ 203 h = strchr(h, *n); 204 if (!h || !n[1]) 205 return (char *)h; 206 if (!h[1]) 207 return 0; 208 if (!n[2]) 209 return twobyte_strstr((void *)h, (void *)n); 210 if (!h[2]) 211 return 0; 212 if (!n[3]) 213 return threebyte_strstr((void *)h, (void *)n); 214 if (!h[3]) 215 return 0; 216 if (!n[4]) 217 return fourbyte_strstr((void *)h, (void *)n); 218 219 return twoway_strstr((void *)h, (void *)n); 220 } 221