1 /* $OpenBSD: strstr.c,v 1.9 2020/04/16 12:37:52 claudio Exp $ */ 2 3 /* 4 * Copyright (c) 2005-2018 Rich Felker 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 26 #include <string.h> 27 #include <stdint.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 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 = n[0]<<24 | n[1]<<16 | n[2]<<8; 41 uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8; 42 for (h+=2; *h && hw != nw; hw = (hw|*++h)<<8); 43 return *h ? (char *)h-2 : 0; 44 } 45 46 static char * 47 fourbyte_strstr(const unsigned char *h, const unsigned char *n) 48 { 49 uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3]; 50 uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3]; 51 for (h+=3; *h && hw != nw; hw = hw<<8 | *++h); 52 return *h ? (char *)h-3 : 0; 53 } 54 55 #define MAX(a,b) ((a)>(b)?(a):(b)) 56 #define MIN(a,b) ((a)<(b)?(a):(b)) 57 58 #define BITOP(a,b,op) \ 59 ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a)))) 60 61 /* 62 * Maxime Crochemore and Dominique Perrin, Two-way string-matching, 63 * Journal of the ACM, 38(3):651-675, July 1991. 64 */ 65 static char * 66 twoway_strstr(const unsigned char *h, const unsigned char *n) 67 { 68 const unsigned char *z; 69 size_t l, ip, jp, k, p, ms, p0, mem, mem0; 70 size_t byteset[32 / sizeof(size_t)] = { 0 }; 71 size_t shift[256]; 72 73 /* Computing length of needle and fill shift table */ 74 for (l=0; n[l] && h[l]; l++) 75 BITOP(byteset, n[l], |=), shift[n[l]] = l+1; 76 if (n[l]) return 0; /* hit the end of h */ 77 78 /* Compute maximal suffix */ 79 ip = -1; jp = 0; k = p = 1; 80 while (jp+k<l) { 81 if (n[ip+k] == n[jp+k]) { 82 if (k == p) { 83 jp += p; 84 k = 1; 85 } else k++; 86 } else if (n[ip+k] > n[jp+k]) { 87 jp += k; 88 k = 1; 89 p = jp - ip; 90 } else { 91 ip = jp++; 92 k = p = 1; 93 } 94 } 95 ms = ip; 96 p0 = p; 97 98 /* And with the opposite comparison */ 99 ip = -1; jp = 0; k = p = 1; 100 while (jp+k<l) { 101 if (n[ip+k] == n[jp+k]) { 102 if (k == p) { 103 jp += p; 104 k = 1; 105 } else k++; 106 } else if (n[ip+k] < n[jp+k]) { 107 jp += k; 108 k = 1; 109 p = jp - ip; 110 } else { 111 ip = jp++; 112 k = p = 1; 113 } 114 } 115 if (ip+1 > ms+1) ms = ip; 116 else p = p0; 117 118 /* Periodic needle? */ 119 if (memcmp(n, n+p, ms+1)) { 120 mem0 = 0; 121 p = MAX(ms, l-ms-1) + 1; 122 } else mem0 = l-p; 123 mem = 0; 124 125 /* Initialize incremental end-of-haystack pointer */ 126 z = h; 127 128 /* Search loop */ 129 for (;;) { 130 /* Update incremental end-of-haystack pointer */ 131 if (z-h < l) { 132 /* Fast estimate for MIN(l,63) */ 133 size_t grow = l | 63; 134 const unsigned char *z2 = memchr(z, 0, grow); 135 if (z2) { 136 z = z2; 137 if (z-h < l) return 0; 138 } else z += grow; 139 } 140 141 /* Check last byte first; advance by shift on mismatch */ 142 if (BITOP(byteset, h[l-1], &)) { 143 k = l-shift[h[l-1]]; 144 if (k) { 145 if (k < mem) k = mem; 146 h += k; 147 mem = 0; 148 continue; 149 } 150 } else { 151 h += l; 152 mem = 0; 153 continue; 154 } 155 156 /* Compare right half */ 157 for (k=MAX(ms+1,mem); n[k] && n[k] == h[k]; k++); 158 if (n[k]) { 159 h += k-ms; 160 mem = 0; 161 continue; 162 } 163 /* Compare left half */ 164 for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--); 165 if (k <= mem) return (char *)h; 166 h += p; 167 mem = mem0; 168 } 169 } 170 171 char * 172 strstr(const char *h, const char *n) 173 { 174 /* Return immediately on empty needle */ 175 if (!n[0]) return (char *)h; 176 177 /* Use faster algorithms for short needles */ 178 h = strchr(h, *n); 179 if (!h || !n[1]) return (char *)h; 180 if (!h[1]) return 0; 181 if (!n[2]) return twobyte_strstr((void *)h, (void *)n); 182 if (!h[2]) return 0; 183 if (!n[3]) return threebyte_strstr((void *)h, (void *)n); 184 if (!h[3]) return 0; 185 if (!n[4]) return fourbyte_strstr((void *)h, (void *)n); 186 187 return twoway_strstr((void *)h, (void *)n); 188 } 189 DEF_STRONG(strstr); 190