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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