[388] | 1 | #include <string.h>
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| 2 | #include <stdint.h>
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| 3 |
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| 4 | static char *twobyte_strstr(const unsigned char *h, const unsigned char *n)
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| 5 | {
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| 6 | uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
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| 7 | for (h++; *h && hw != nw; hw = hw<<8 | *++h);
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| 8 | return *h ? (char *)h-1 : 0;
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| 9 | }
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| 10 |
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| 11 | static char *threebyte_strstr(const unsigned char *h, const unsigned char *n)
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| 12 | {
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| 13 | uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
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| 14 | uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
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| 15 | for (h+=2; *h && hw != nw; hw = (hw|*++h)<<8);
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| 16 | return *h ? (char *)h-2 : 0;
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| 17 | }
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| 18 |
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| 19 | static char *fourbyte_strstr(const unsigned char *h, const unsigned char *n)
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| 20 | {
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| 21 | uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
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| 22 | uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
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| 23 | for (h+=3; *h && hw != nw; hw = hw<<8 | *++h);
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| 24 | return *h ? (char *)h-3 : 0;
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| 25 | }
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| 26 |
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| 27 | #define MAX(a,b) ((a)>(b)?(a):(b))
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| 28 | #define MIN(a,b) ((a)<(b)?(a):(b))
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| 29 |
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| 30 | #define BITOP(a,b,op) \
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| 31 | ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
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| 32 |
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| 33 | static char *twoway_strstr(const unsigned char *h, const unsigned char *n)
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| 34 | {
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| 35 | const unsigned char *z;
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| 36 | size_t l, ip, jp, k, p, ms, p0, mem, mem0;
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| 37 | size_t byteset[32 / sizeof(size_t)] = { 0 };
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| 38 | size_t shift[256];
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| 39 |
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| 40 | /* Computing length of needle and fill shift table */
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| 41 | for (l=0; n[l] && h[l]; l++)
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| 42 | BITOP(byteset, n[l], |=), shift[n[l]] = l+1;
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| 43 | if (n[l]) return 0; /* hit the end of h */
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| 44 |
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| 45 | /* Compute maximal suffix */
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| 46 | ip = -1; jp = 0; k = p = 1;
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| 47 | while (jp+k<l) {
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| 48 | if (n[ip+k] == n[jp+k]) {
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| 49 | if (k == p) {
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| 50 | jp += p;
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| 51 | k = 1;
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| 52 | } else k++;
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| 53 | } else if (n[ip+k] > n[jp+k]) {
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| 54 | jp += k;
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| 55 | k = 1;
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| 56 | p = jp - ip;
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| 57 | } else {
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| 58 | ip = jp++;
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| 59 | k = p = 1;
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| 60 | }
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| 61 | }
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| 62 | ms = ip;
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| 63 | p0 = p;
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| 64 |
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| 65 | /* And with the opposite comparison */
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| 66 | ip = -1; jp = 0; k = p = 1;
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| 67 | while (jp+k<l) {
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| 68 | if (n[ip+k] == n[jp+k]) {
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| 69 | if (k == p) {
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| 70 | jp += p;
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| 71 | k = 1;
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| 72 | } else k++;
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| 73 | } else if (n[ip+k] < n[jp+k]) {
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| 74 | jp += k;
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| 75 | k = 1;
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| 76 | p = jp - ip;
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| 77 | } else {
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| 78 | ip = jp++;
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| 79 | k = p = 1;
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| 80 | }
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| 81 | }
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| 82 | if (ip+1 > ms+1) ms = ip;
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| 83 | else p = p0;
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| 84 |
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| 85 | /* Periodic needle? */
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| 86 | if (memcmp(n, n+p, ms+1)) {
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| 87 | mem0 = 0;
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| 88 | p = MAX(ms, l-ms-1) + 1;
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| 89 | } else mem0 = l-p;
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| 90 | mem = 0;
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| 91 |
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| 92 | /* Initialize incremental end-of-haystack pointer */
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| 93 | z = h;
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| 94 |
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| 95 | /* Search loop */
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| 96 | for (;;) {
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| 97 | /* Update incremental end-of-haystack pointer */
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| 98 | if (z-h < l) {
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| 99 | /* Fast estimate for MIN(l,63) */
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| 100 | size_t grow = l | 63;
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| 101 | const unsigned char *z2 = memchr(z, 0, grow);
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| 102 | if (z2) {
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| 103 | z = z2;
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| 104 | if (z-h < l) return 0;
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| 105 | } else z += grow;
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| 106 | }
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| 107 |
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| 108 | /* Check last byte first; advance by shift on mismatch */
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| 109 | if (BITOP(byteset, h[l-1], &)) {
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| 110 | k = l-shift[h[l-1]];
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| 111 | //printf("adv by %zu (on %c) at [%s] (%zu;l=%zu)\n", k, h[l-1], h, shift[h[l-1]], l);
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| 112 | if (k) {
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| 113 | if (mem0 && mem && k < p) k = l-p;
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| 114 | h += k;
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| 115 | mem = 0;
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| 116 | continue;
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| 117 | }
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| 118 | } else {
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| 119 | h += l;
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| 120 | mem = 0;
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| 121 | continue;
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| 122 | }
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| 123 |
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| 124 | /* Compare right half */
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| 125 | for (k=MAX(ms+1,mem); n[k] && n[k] == h[k]; k++);
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| 126 | if (n[k]) {
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| 127 | h += k-ms;
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| 128 | mem = 0;
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| 129 | continue;
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| 130 | }
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| 131 | /* Compare left half */
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| 132 | for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
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| 133 | if (k <= mem) return (char *)h;
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| 134 | h += p;
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| 135 | mem = mem0;
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| 136 | }
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| 137 | }
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| 138 |
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| 139 | char *strstr(const char *h, const char *n)
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| 140 | {
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| 141 | /* Return immediately on empty needle */
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| 142 | if (!n[0]) return (char *)h;
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| 143 |
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| 144 | /* Use faster algorithms for short needles */
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| 145 | h = strchr(h, *n);
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| 146 | if (!h || !n[1]) return (char *)h;
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| 147 | if (!h[1]) return 0;
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| 148 | if (!n[2]) return twobyte_strstr((void *)h, (void *)n);
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| 149 | if (!h[2]) return 0;
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| 150 | if (!n[3]) return threebyte_strstr((void *)h, (void *)n);
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| 151 | if (!h[3]) return 0;
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| 152 | if (!n[4]) return fourbyte_strstr((void *)h, (void *)n);
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| 153 |
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| 154 | return twoway_strstr((void *)h, (void *)n);
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| 155 | }
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