1 /* $OpenBSD: memmem.c,v 1.5 2020/04/16 12:39:28 claudio Exp $ */ 2 3 /* 4 * Copyright (c) 2005-2020 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 26 #include <string.h> 27 #include <stdint.h> 28 29 static char * 30 twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) 31 { 32 uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1]; 33 for (h+=2, k-=2; k; k--, hw = hw<<8 | *h++) 34 if (hw == nw) 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 = n[0]<<24 | n[1]<<16 | n[2]<<8; 42 uint32_t hw = 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) return (char *)h-3; 45 return hw == nw ? (char *)h-3 : 0; 46 } 47 48 static char * 49 fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) 50 { 51 uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3]; 52 uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3]; 53 for (h+=4, k-=4; k; k--, hw = hw<<8 | *h++) 54 if (hw == nw) return (char *)h-4; 55 return hw == nw ? (char *)h-4 : 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 (size_t)1<<((size_t)(b)%(8*sizeof *(a)))) 63 64 /* 65 * Maxime Crochemore and Dominique Perrin, Two-way string-matching, 66 * Journal of the ACM, 38(3):651-675, July 1991. 67 */ 68 static char * 69 twoway_memmem(const unsigned char *h, const unsigned char *z, 70 const unsigned char *n, size_t l) 71 { 72 size_t i, ip, jp, k, p, ms, p0, mem, mem0; 73 size_t byteset[32 / sizeof(size_t)] = { 0 }; 74 size_t shift[256]; 75 76 /* Computing length of needle and fill shift table */ 77 for (i=0; i<l; i++) 78 BITOP(byteset, n[i], |=), shift[n[i]] = i+1; 79 80 /* Compute maximal suffix */ 81 ip = -1; jp = 0; k = p = 1; 82 while (jp+k<l) { 83 if (n[ip+k] == n[jp+k]) { 84 if (k == p) { 85 jp += p; 86 k = 1; 87 } else k++; 88 } else if (n[ip+k] > n[jp+k]) { 89 jp += k; 90 k = 1; 91 p = jp - ip; 92 } else { 93 ip = jp++; 94 k = p = 1; 95 } 96 } 97 ms = ip; 98 p0 = p; 99 100 /* And with the opposite comparison */ 101 ip = -1; jp = 0; k = p = 1; 102 while (jp+k<l) { 103 if (n[ip+k] == n[jp+k]) { 104 if (k == p) { 105 jp += p; 106 k = 1; 107 } else k++; 108 } else if (n[ip+k] < n[jp+k]) { 109 jp += k; 110 k = 1; 111 p = jp - ip; 112 } else { 113 ip = jp++; 114 k = p = 1; 115 } 116 } 117 if (ip+1 > ms+1) ms = ip; 118 else p = p0; 119 120 /* Periodic needle? */ 121 if (memcmp(n, n+p, ms+1)) { 122 mem0 = 0; 123 p = MAX(ms, l-ms-1) + 1; 124 } else mem0 = l-p; 125 mem = 0; 126 127 /* Search loop */ 128 for (;;) { 129 /* If remainder of haystack is shorter than needle, done */ 130 if (z-h < l) return 0; 131 132 /* Check last byte first; advance by shift on mismatch */ 133 if (BITOP(byteset, h[l-1], &)) { 134 k = l-shift[h[l-1]]; 135 if (k) { 136 if (k < mem) k = mem; 137 h += k; 138 mem = 0; 139 continue; 140 } 141 } else { 142 h += l; 143 mem = 0; 144 continue; 145 } 146 147 /* Compare right half */ 148 for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++); 149 if (k < l) { 150 h += k-ms; 151 mem = 0; 152 continue; 153 } 154 /* Compare left half */ 155 for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--); 156 if (k <= mem) return (char *)h; 157 h += p; 158 mem = mem0; 159 } 160 } 161 162 void * 163 memmem(const void *h0, size_t k, const void *n0, size_t l) 164 { 165 const unsigned char *h = h0, *n = n0; 166 167 /* Return immediately on empty needle */ 168 if (!l) return (void *)h; 169 170 /* Return immediately when needle is longer than haystack */ 171 if (k<l) return 0; 172 173 /* Use faster algorithms for short needles */ 174 h = memchr(h0, *n, k); 175 if (!h || l==1) return (void *)h; 176 k -= h - (const unsigned char *)h0; 177 if (k<l) return 0; 178 if (l==2) return twobyte_memmem(h, k, n); 179 if (l==3) return threebyte_memmem(h, k, n); 180 if (l==4) return fourbyte_memmem(h, k, n); 181 182 return twoway_memmem(h, h+k, n, l); 183 } 184 DEF_WEAK(memmem); 185