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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