1#define _GNU_SOURCE 2#include <string.h> 3#include <stdint.h> 4 5static char *twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) 6{ 7 uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1]; 8 for (h++, k--; k; k--, hw = hw<<8 | *++h) 9 if (hw == nw) return (char *)h-1; 10 return 0; 11} 12 13static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) 14{ 15 uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8; 16 uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8; 17 for (h+=2, k-=2; k; k--, hw = (hw|*++h)<<8) 18 if (hw == nw) return (char *)h-2; 19 return 0; 20} 21 22static char *fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) 23{ 24 uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3]; 25 uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3]; 26 for (h+=3, k-=3; k; k--, hw = hw<<8 | *++h) 27 if (hw == nw) return (char *)h-3; 28 return 0; 29} 30 31#define MAX(a,b) ((a)>(b)?(a):(b)) 32#define MIN(a,b) ((a)<(b)?(a):(b)) 33 34#define BITOP(a,b,op) \ 35 ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a)))) 36 37static char *twoway_memmem(const unsigned char *h, const unsigned char *z, const unsigned char *n, size_t l) 38{ 39 size_t i, ip, jp, k, p, ms, p0, mem, mem0; 40 size_t byteset[32 / sizeof(size_t)] = { 0 }; 41 size_t shift[256]; 42 43 /* Computing length of needle and fill shift table */ 44 for (i=0; i<l; i++) 45 BITOP(byteset, n[i], |=), shift[n[i]] = i+1; 46 47 /* Compute maximal suffix */ 48 ip = -1; jp = 0; k = p = 1; 49 while (jp+k<l) { 50 if (n[ip+k] == n[jp+k]) { 51 if (k == p) { 52 jp += p; 53 k = 1; 54 } else k++; 55 } else if (n[ip+k] > n[jp+k]) { 56 jp += k; 57 k = 1; 58 p = jp - ip; 59 } else { 60 ip = jp++; 61 k = p = 1; 62 } 63 } 64 ms = ip; 65 p0 = p; 66 67 /* And with the opposite comparison */ 68 ip = -1; jp = 0; k = p = 1; 69 while (jp+k<l) { 70 if (n[ip+k] == n[jp+k]) { 71 if (k == p) { 72 jp += p; 73 k = 1; 74 } else k++; 75 } else if (n[ip+k] < n[jp+k]) { 76 jp += k; 77 k = 1; 78 p = jp - ip; 79 } else { 80 ip = jp++; 81 k = p = 1; 82 } 83 } 84 if (ip+1 > ms+1) ms = ip; 85 else p = p0; 86 87 /* Periodic needle? */ 88 if (memcmp(n, n+p, ms+1)) { 89 mem0 = 0; 90 p = MAX(ms, l-ms-1) + 1; 91 } else mem0 = l-p; 92 mem = 0; 93 94 /* Search loop */ 95 for (;;) { 96 /* If remainder of haystack is shorter than needle, done */ 97 if (z-h < l) return 0; 98 99 /* Check last byte first; advance by shift on mismatch */ 100 if (BITOP(byteset, h[l-1], &)) { 101 k = l-shift[h[l-1]]; 102 if (k) { 103 if (mem0 && mem && k < p) k = l-p; 104 h += k; 105 mem = 0; 106 continue; 107 } 108 } else { 109 h += l; 110 mem = 0; 111 continue; 112 } 113 114 /* Compare right half */ 115 for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++); 116 if (k < l) { 117 h += k-ms; 118 mem = 0; 119 continue; 120 } 121 /* Compare left half */ 122 for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--); 123 if (k <= mem) return (char *)h; 124 h += p; 125 mem = mem0; 126 } 127} 128 129void *memmem(const void *h0, size_t k, const void *n0, size_t l) 130{ 131 const unsigned char *h = h0, *n = n0; 132 133 /* Return immediately on empty needle */ 134 if (!l) return (void *)h; 135 136 /* Return immediately when needle is longer than haystack */ 137 if (k<l) return 0; 138 139 /* Use faster algorithms for short needles */ 140 h = memchr(h0, *n, k); 141 if (!h || l==1) return (void *)h; 142 k -= h - (const unsigned char *)h0; 143 if (k<l) return 0; 144 if (l==2) return twobyte_memmem(h, k, n); 145 if (l==3) return threebyte_memmem(h, k, n); 146 if (l==4) return fourbyte_memmem(h, k, n); 147 148 return twoway_memmem(h, h+k, n, l); 149} 150