1 | #include <wchar.h>
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2 |
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3 | #define MAX(a,b) ((a)>(b)?(a):(b))
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4 | #define MIN(a,b) ((a)<(b)?(a):(b))
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5 |
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6 | static wchar_t *twoway_wcsstr(const wchar_t *h, const wchar_t *n)
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7 | {
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8 | const wchar_t *z;
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9 | size_t l, ip, jp, k, p, ms, p0, mem, mem0;
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10 |
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11 | /* Computing length of needle */
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12 | for (l=0; n[l] && h[l]; l++);
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13 | if (n[l]) return 0; /* hit the end of h */
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14 |
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15 | /* Compute maximal suffix */
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16 | ip = -1; jp = 0; k = p = 1;
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17 | while (jp+k<l) {
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18 | if (n[ip+k] == n[jp+k]) {
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19 | if (k == p) {
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20 | jp += p;
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21 | k = 1;
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22 | } else k++;
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23 | } else if (n[ip+k] > n[jp+k]) {
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24 | jp += k;
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25 | k = 1;
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26 | p = jp - ip;
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27 | } else {
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28 | ip = jp++;
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29 | k = p = 1;
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30 | }
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31 | }
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32 | ms = ip;
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33 | p0 = p;
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34 |
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35 | /* And with the opposite comparison */
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36 | ip = -1; jp = 0; k = p = 1;
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37 | while (jp+k<l) {
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38 | if (n[ip+k] == n[jp+k]) {
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39 | if (k == p) {
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40 | jp += p;
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41 | k = 1;
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42 | } else k++;
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43 | } else if (n[ip+k] < n[jp+k]) {
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44 | jp += k;
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45 | k = 1;
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46 | p = jp - ip;
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47 | } else {
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48 | ip = jp++;
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49 | k = p = 1;
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50 | }
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51 | }
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52 | if (ip+1 > ms+1) ms = ip;
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53 | else p = p0;
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54 |
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55 | /* Periodic needle? */
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56 | if (wmemcmp(n, n+p, ms+1)) {
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57 | mem0 = 0;
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58 | p = MAX(ms, l-ms-1) + 1;
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59 | } else mem0 = l-p;
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60 | mem = 0;
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61 |
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62 | /* Initialize incremental end-of-haystack pointer */
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63 | z = h;
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64 |
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65 | /* Search loop */
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66 | for (;;) {
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67 | /* Update incremental end-of-haystack pointer */
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68 | if (z-h < l) {
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69 | /* Fast estimate for MIN(l,63) */
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70 | size_t grow = l | 63;
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71 | const wchar_t *z2 = wmemchr(z, 0, grow);
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72 | if (z2) {
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73 | z = z2;
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74 | if (z-h < l) return 0;
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75 | } else z += grow;
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76 | }
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77 |
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78 | /* Compare right half */
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79 | for (k=MAX(ms+1,mem); n[k] && n[k] == h[k]; k++);
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80 | if (n[k]) {
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81 | h += k-ms;
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82 | mem = 0;
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83 | continue;
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84 | }
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85 | /* Compare left half */
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86 | for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
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87 | if (k <= mem) return (wchar_t *)h;
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88 | h += p;
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89 | mem = mem0;
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90 | }
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91 | }
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92 |
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93 | wchar_t *wcsstr(const wchar_t *restrict h, const wchar_t *restrict n)
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94 | {
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95 | /* Return immediately on empty needle or haystack */
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96 | if (!n[0]) return (wchar_t *)h;
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97 | if (!h[0]) return 0;
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98 |
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99 | /* Use faster algorithms for short needles */
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100 | h = wcschr(h, *n);
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101 | if (!h || !n[1]) return (wchar_t *)h;
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102 | if (!h[1]) return 0;
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103 |
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104 | return twoway_wcsstr(h, n);
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105 | }
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