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