[398] | 1 | #define _GNU_SOURCE
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| 2 | #include <string.h>
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| 3 | #include <stdint.h>
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| 4 |
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| 5 | static char *twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
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| 6 | {
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| 7 | uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
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| 8 | for (h+=2, k-=2; k; k--, hw = hw<<8 | *h++)
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| 9 | if (hw == nw) return (char *)h-2;
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| 10 | return hw == nw ? (char *)h-2 : 0;
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| 11 | }
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| 12 |
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| 13 | static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
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| 14 | {
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| 15 | uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
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| 16 | uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
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| 17 | for (h+=3, k-=3; k; k--, hw = (hw|*h++)<<8)
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| 18 | if (hw == nw) return (char *)h-3;
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| 19 | return hw == nw ? (char *)h-3 : 0;
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| 20 | }
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| 21 |
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| 22 | static char *fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
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| 23 | {
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| 24 | uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
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| 25 | uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
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| 26 | for (h+=4, k-=4; k; k--, hw = hw<<8 | *h++)
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| 27 | if (hw == nw) return (char *)h-4;
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| 28 | return hw == nw ? (char *)h-4 : 0;
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| 29 | }
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| 30 |
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| 31 | #define MAX(a,b) ((a)>(b)?(a):(b))
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| 32 | #define MIN(a,b) ((a)<(b)?(a):(b))
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| 33 |
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| 34 | #define BITOP(a,b,op) \
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| 35 | ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
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| 36 |
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| 37 | static char *twoway_memmem(const unsigned char *h, const unsigned char *z, const unsigned char *n, size_t l)
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| 38 | {
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| 39 | size_t i, ip, jp, k, p, ms, p0, mem, mem0;
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| 40 | size_t byteset[32 / sizeof(size_t)] = { 0 };
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| 41 | size_t shift[256];
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| 42 |
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| 43 | /* Computing length of needle and fill shift table */
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| 44 | for (i=0; i<l; i++)
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| 45 | BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
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| 46 |
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| 47 | /* Compute maximal suffix */
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| 48 | ip = -1; jp = 0; k = p = 1;
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| 49 | while (jp+k<l) {
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| 50 | if (n[ip+k] == n[jp+k]) {
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| 51 | if (k == p) {
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| 52 | jp += p;
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| 53 | k = 1;
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| 54 | } else k++;
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| 55 | } else if (n[ip+k] > n[jp+k]) {
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| 56 | jp += k;
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| 57 | k = 1;
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| 58 | p = jp - ip;
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| 59 | } else {
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| 60 | ip = jp++;
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| 61 | k = p = 1;
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| 62 | }
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| 63 | }
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| 64 | ms = ip;
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| 65 | p0 = p;
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| 66 |
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| 67 | /* And with the opposite comparison */
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| 68 | ip = -1; jp = 0; k = p = 1;
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| 69 | while (jp+k<l) {
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| 70 | if (n[ip+k] == n[jp+k]) {
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| 71 | if (k == p) {
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| 72 | jp += p;
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| 73 | k = 1;
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| 74 | } else k++;
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| 75 | } else if (n[ip+k] < n[jp+k]) {
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| 76 | jp += k;
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| 77 | k = 1;
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| 78 | p = jp - ip;
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| 79 | } else {
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| 80 | ip = jp++;
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| 81 | k = p = 1;
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| 82 | }
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| 83 | }
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| 84 | if (ip+1 > ms+1) ms = ip;
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| 85 | else p = p0;
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| 86 |
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| 87 | /* Periodic needle? */
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| 88 | if (memcmp(n, n+p, ms+1)) {
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| 89 | mem0 = 0;
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| 90 | p = MAX(ms, l-ms-1) + 1;
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| 91 | } else mem0 = l-p;
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| 92 | mem = 0;
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| 93 |
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| 94 | /* Search loop */
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| 95 | for (;;) {
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| 96 | /* If remainder of haystack is shorter than needle, done */
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| 97 | if (z-h < l) return 0;
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| 98 |
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| 99 | /* Check last byte first; advance by shift on mismatch */
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| 100 | if (BITOP(byteset, h[l-1], &)) {
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| 101 | k = l-shift[h[l-1]];
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| 102 | if (k) {
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| 103 | if (mem0 && mem && k < p) k = l-p;
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| 104 | h += k;
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| 105 | mem = 0;
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| 106 | continue;
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| 107 | }
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| 108 | } else {
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| 109 | h += l;
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| 110 | mem = 0;
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| 111 | continue;
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| 112 | }
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| 113 |
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| 114 | /* Compare right half */
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| 115 | for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++);
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| 116 | if (k < l) {
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| 117 | h += k-ms;
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| 118 | mem = 0;
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| 119 | continue;
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| 120 | }
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| 121 | /* Compare left half */
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| 122 | for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
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| 123 | if (k <= mem) return (char *)h;
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| 124 | h += p;
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| 125 | mem = mem0;
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| 126 | }
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| 127 | }
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| 128 |
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| 129 | void *memmem(const void *h0, size_t k, const void *n0, size_t l)
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| 130 | {
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| 131 | const unsigned char *h = h0, *n = n0;
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| 132 |
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| 133 | /* Return immediately on empty needle */
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| 134 | if (!l) return (void *)h;
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| 135 |
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| 136 | /* Return immediately when needle is longer than haystack */
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| 137 | if (k<l) return 0;
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| 138 |
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| 139 | /* Use faster algorithms for short needles */
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| 140 | h = memchr(h0, *n, k);
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| 141 | if (!h || l==1) return (void *)h;
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| 142 | k -= h - (const unsigned char *)h0;
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| 143 | if (k<l) return 0;
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| 144 | if (l==2) return twobyte_memmem(h, k, n);
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| 145 | if (l==3) return threebyte_memmem(h, k, n);
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| 146 | if (l==4) return fourbyte_memmem(h, k, n);
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| 147 |
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| 148 | return twoway_memmem(h, h+k, n, l);
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| 149 | }
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