1 | #ifndef __HALTON_H
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2 | #define __HALTON_H
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3 |
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4 | #include <iostream>
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5 | using namespace std;
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6 |
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7 | namespace GtpVisibilityPreprocessor {
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8 |
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9 | inline float halton(float baseRec, float prev) {
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10 | float r = 1 - prev - 1e-10f;
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11 | if (baseRec < r)
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12 | return prev + baseRec;
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13 | float h = baseRec;
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14 | float hh;
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15 | do {
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16 | hh = h;
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17 | h *= baseRec;
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18 | } while (h >= r);
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19 | return prev + hh + h - 1;
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20 | }
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21 |
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22 | template<int T>
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23 | class Halton {
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24 | float _invBases[T];
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25 | float _prev[T];
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26 |
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27 | public:
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28 |
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29 | void Reset() {
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30 | for (int i=0; i < T; i++)
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31 | _prev[i] = 0;
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32 | }
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33 |
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34 | Halton() {
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35 | for (int i=0; i < T; i++) {
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36 | int base = FindPrime(i+1);
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37 | if (base == 1)
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38 | base++;
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39 | _invBases[i] = 1.0f/base;
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40 | }
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41 | Reset();
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42 | }
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43 |
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44 | void
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45 | GetNext(float *a) {
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46 | for (int i=0; i < T; i++) {
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47 | a[i] = halton(_invBases[i], _prev[i]);
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48 | _prev[i] = a[i];
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49 | }
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50 | }
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51 |
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52 | };
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53 |
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54 | class Halton2 {
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55 | static float _invBases[2];
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56 | float _prev[2];
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57 |
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58 | public:
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59 |
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60 | void Reset() {
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61 | _prev[0] =_prev[1] = 0;
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62 | }
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63 |
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64 | Halton2() {
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65 | _invBases[0] = 1.0f/2;
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66 | _invBases[1] = 1.0f/3;
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67 | Reset();
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68 | }
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69 |
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70 | void
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71 | GetNext(float &a, float &b) {
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72 | a = halton(_invBases[0], _prev[0]);
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73 | b = halton(_invBases[1], _prev[1]);
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74 | _prev[0] = a;
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75 | _prev[1] = b;
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76 | }
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77 | };
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78 |
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79 |
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80 | /**
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81 | * Assert whether the argument is a prime number.
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82 | * @param number the number to be checked
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83 | */
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84 | inline bool IsPrime(const int number) {
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85 | bool isIt = true;
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86 | for(int i = 2; i < number; i++) {
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87 | if(number % i == 0) {
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88 | isIt = false;
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89 | break;
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90 | }
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91 | }
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92 | if(number == 2) {
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93 | isIt = false;
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94 | }
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95 | return isIt;
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96 | }
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97 |
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98 | /**
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99 | * Find the nth prime number.
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100 | * @param index the ordinal position in the sequence
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101 | */
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102 | inline int FindPrime(const int index) {
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103 | // if (index < 1) {
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104 | // cerr<<"FindPrime: The argument must be non-negative."<<endl;
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105 | // return -1;
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106 | // }
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107 |
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108 | const int primes[] = {-1, 1, 3, 5, 7, 11, 13};
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109 | if (index <= 6)
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110 | return primes[index];
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111 |
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112 | int prime = 1;
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113 | int found = 1;
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114 | while(found != index) {
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115 | prime += 2;
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116 | if(IsPrime(prime) == true) {
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117 | found++;
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118 | }
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119 | }
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120 | return prime;
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121 | }
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122 |
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123 | struct HaltonSequence {
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124 | public:
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125 | int index;
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126 |
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127 | HaltonSequence():index(1) {}
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128 |
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129 | void Reset() {
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130 | index = 1;
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131 | }
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132 |
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133 | void GenerateNext() {
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134 | index++;
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135 | }
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136 |
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137 | /**
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138 | * Returns the nth number in the sequence, taken from a specified dimension.
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139 | * @param index the ordinal position in the sequence
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140 | * @param dimension the dimension
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141 | */
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142 |
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143 | double GetNumber(const int dimension) {
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144 | int base = FindPrime(dimension);
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145 | if(base == 1) {
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146 | base++; //The first dimension uses base 2.
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147 | }
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148 | double remainder;
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149 | double output = 0.0;
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150 | double fraction = 1.0 / (double)base;
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151 | int N1 = 0;
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152 | int copyOfIndex = index;
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153 | if((base >= 2) && (index >= 1)) {
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154 | while(copyOfIndex > 0) {
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155 | N1 = (copyOfIndex / base);
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156 | remainder = copyOfIndex % base;
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157 | output += fraction * remainder;
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158 | copyOfIndex = (int)(copyOfIndex / base);
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159 | fraction /= (double)base;
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160 | }
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161 | return output;
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162 | }
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163 | else {
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164 | cerr<<"Error generating Halton sequence."<<endl;
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165 | exit(1);
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166 | }
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167 | }
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168 | };
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169 |
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170 | extern Halton2 halton2;
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171 | }
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172 |
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173 | #endif
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