1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 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_strstr(const unsigned char *h, const unsigned char *n) 33 { 34 uint16_t nw = n[0] << 8 | n[1], hw = h[0] << 8 | h[1]; 35 for (h++; *h && hw != nw; hw = hw << 8 | *++h) 36 ; 37 return *h ? (char *)h - 1 : 0; 38 } 39 40 static char * 41 threebyte_strstr(const unsigned char *h, const unsigned char *n) 42 { 43 uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8; 44 uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8; 45 for (h += 2; *h && hw != nw; hw = (hw | *++h) << 8) 46 ; 47 return *h ? (char *)h - 2 : 0; 48 } 49 50 static char * 51 fourbyte_strstr(const unsigned char *h, 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 += 3; *h && hw != nw; hw = hw << 8 | *++h) 56 ; 57 return *h ? (char *)h - 3 : 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_strstr(const unsigned char *h, const unsigned char *n) 77 { 78 const unsigned char *z; 79 size_t l, 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 (l = 0; n[l] && h[l]; l++) 85 BITOP(byteset, n[l], |=), shift[n[l]] = l + 1; 86 if (n[l]) 87 return 0; /* hit the end of h */ 88 89 /* Compute maximal suffix */ 90 ip = -1; 91 jp = 0; 92 k = p = 1; 93 while (jp + k < l) { 94 if (n[ip + k] == n[jp + k]) { 95 if (k == p) { 96 jp += p; 97 k = 1; 98 } else 99 k++; 100 } else if (n[ip + k] > n[jp + k]) { 101 jp += k; 102 k = 1; 103 p = jp - ip; 104 } else { 105 ip = jp++; 106 k = p = 1; 107 } 108 } 109 ms = ip; 110 p0 = p; 111 112 /* And with the opposite comparison */ 113 ip = -1; 114 jp = 0; 115 k = p = 1; 116 while (jp + k < l) { 117 if (n[ip + k] == n[jp + k]) { 118 if (k == p) { 119 jp += p; 120 k = 1; 121 } else 122 k++; 123 } else if (n[ip + k] < n[jp + k]) { 124 jp += k; 125 k = 1; 126 p = jp - ip; 127 } else { 128 ip = jp++; 129 k = p = 1; 130 } 131 } 132 if (ip + 1 > ms + 1) 133 ms = ip; 134 else 135 p = p0; 136 137 /* Periodic needle? */ 138 if (memcmp(n, n + p, ms + 1)) { 139 mem0 = 0; 140 p = MAX(ms, l - ms - 1) + 1; 141 } else 142 mem0 = l - p; 143 mem = 0; 144 145 /* Initialize incremental end-of-haystack pointer */ 146 z = h; 147 148 /* Search loop */ 149 for (;;) { 150 /* Update incremental end-of-haystack pointer */ 151 if (z - h < l) { 152 /* Fast estimate for MIN(l,63) */ 153 size_t grow = l | 63; 154 const unsigned char *z2 = memchr(z, 0, grow); 155 if (z2) { 156 z = z2; 157 if (z - h < l) 158 return 0; 159 } else 160 z += grow; 161 } 162 163 /* Check last byte first; advance by shift on mismatch */ 164 if (BITOP(byteset, h[l - 1], &)) { 165 k = l - shift[h[l - 1]]; 166 if (k) { 167 if (k < mem) 168 k = mem; 169 h += k; 170 mem = 0; 171 continue; 172 } 173 } else { 174 h += l; 175 mem = 0; 176 continue; 177 } 178 179 /* Compare right half */ 180 for (k = MAX(ms + 1, mem); n[k] && n[k] == h[k]; k++) 181 ; 182 if (n[k]) { 183 h += k - ms; 184 mem = 0; 185 continue; 186 } 187 /* Compare left half */ 188 for (k = ms + 1; k > mem && n[k - 1] == h[k - 1]; k--) 189 ; 190 if (k <= mem) 191 return (char *)h; 192 h += p; 193 mem = mem0; 194 } 195 } 196 197 char * 198 strstr(const char *h, const char *n) 199 { 200 /* Return immediately on empty needle */ 201 if (!n[0]) 202 return (char *)h; 203 204 /* Use faster algorithms for short needles */ 205 h = strchr(h, *n); 206 if (!h || !n[1]) 207 return (char *)h; 208 if (!h[1]) 209 return 0; 210 if (!n[2]) 211 return twobyte_strstr((void *)h, (void *)n); 212 if (!h[2]) 213 return 0; 214 if (!n[3]) 215 return threebyte_strstr((void *)h, (void *)n); 216 if (!h[3]) 217 return 0; 218 if (!n[4]) 219 return fourbyte_strstr((void *)h, (void *)n); 220 221 return twoway_strstr((void *)h, (void *)n); 222 } 223