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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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 | #include <string.h> #include <stdint.h> static char *twobyte_strstr(const unsigned char *h, const unsigned char *n) { uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1]; for (h++; *h && hw != nw; hw = hw<<8 | *++h); return *h ? (char *)h-1 : 0; } static char *threebyte_strstr(const unsigned char *h, 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+=2; *h && hw != nw; hw = (hw|*++h)<<8); return *h ? (char *)h-2 : 0; } static char *fourbyte_strstr(const unsigned char *h, 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+=3; *h && hw != nw; hw = hw<<8 | *++h); return *h ? (char *)h-3 : 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_strstr(const unsigned char *h, const unsigned char *n) { const unsigned char *z; size_t l, 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 (l=0; n[l] && h[l]; l++) BITOP(byteset, n[l], |=), shift[n[l]] = l+1; if (n[l]) return 0; /* hit the end of h */ /* 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; /* Initialize incremental end-of-haystack pointer */ z = h; /* Search loop */ for (;;) { /* Update incremental end-of-haystack pointer */ if (z-h < l) { /* Fast estimate for MIN(l,63) */ size_t grow = l | 63; const unsigned char *z2 = memchr(z, 0, grow); if (z2) { z = z2; if (z-h < l) return 0; } else z += grow; } /* 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); n[k] && n[k] == h[k]; k++); if (n[k]) { 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; } } char *strstr(const char *h, const char *n) { /* Return immediately on empty needle */ if (!n[0]) return (char *)h; /* Use faster algorithms for short needles */ h = strchr(h, *n); if (!h || !n[1]) return (char *)h; if (!h[1]) return 0; if (!n[2]) return twobyte_strstr((void *)h, (void *)n); if (!h[2]) return 0; if (!n[3]) return threebyte_strstr((void *)h, (void *)n); if (!h[3]) return 0; if (!n[4]) return fourbyte_strstr((void *)h, (void *)n); return twoway_strstr((void *)h, (void *)n); } |