1 | /* glprng01.c */ |
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2 | |
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3 | /*********************************************************************** |
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4 | * This code is part of GLPK (GNU Linear Programming Kit). |
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5 | * |
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6 | * This code is a modified version of the module GB_FLIP, a portable |
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7 | * pseudo-random number generator. The original version of GB_FLIP is |
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8 | * a part of The Stanford GraphBase developed by Donald E. Knuth (see |
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9 | * http://www-cs-staff.stanford.edu/~knuth/sgb.html). |
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10 | * |
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11 | * Note that all changes concern only external names, so this modified |
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12 | * version produces exactly the same results as the original version. |
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13 | * |
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14 | * Changes were made by Andrew Makhorin <mao@gnu.org>. |
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15 | * |
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16 | * GLPK is free software: you can redistribute it and/or modify it |
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17 | * under the terms of the GNU General Public License as published by |
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18 | * the Free Software Foundation, either version 3 of the License, or |
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19 | * (at your option) any later version. |
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20 | * |
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21 | * GLPK is distributed in the hope that it will be useful, but WITHOUT |
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22 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
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23 | * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public |
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24 | * License for more details. |
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25 | * |
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26 | * You should have received a copy of the GNU General Public License |
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27 | * along with GLPK. If not, see <http://www.gnu.org/licenses/>. |
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28 | ***********************************************************************/ |
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29 | |
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30 | #include "glpenv.h" |
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31 | #include "glprng.h" |
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32 | |
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33 | #if 0 |
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34 | int A[56] = { -1 }; |
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35 | #else |
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36 | #define A (rand->A) |
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37 | #endif |
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38 | /* pseudo-random values */ |
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39 | |
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40 | #if 0 |
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41 | int *fptr = A; |
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42 | #else |
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43 | #define fptr (rand->fptr) |
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44 | #endif |
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45 | /* the next A value to be exported */ |
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46 | |
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47 | #define mod_diff(x, y) (((x) - (y)) & 0x7FFFFFFF) |
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48 | /* difference modulo 2^31 */ |
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49 | |
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50 | static int flip_cycle(RNG *rand) |
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51 | { /* this is an auxiliary routine to do 55 more steps of the basic |
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52 | recurrence, at high speed, and to reset fptr */ |
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53 | int *ii, *jj; |
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54 | for (ii = &A[1], jj = &A[32]; jj <= &A[55]; ii++, jj++) |
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55 | *ii = mod_diff(*ii, *jj); |
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56 | for (jj = &A[1]; ii <= &A[55]; ii++, jj++) |
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57 | *ii = mod_diff(*ii, *jj); |
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58 | fptr = &A[54]; |
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59 | return A[55]; |
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60 | } |
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61 | |
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62 | /*********************************************************************** |
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63 | * NAME |
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64 | * |
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65 | * rng_create_rand - create pseudo-random number generator |
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66 | * |
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67 | * SYNOPSIS |
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68 | * |
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69 | * #include "glprng.h" |
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70 | * RNG *rng_create_rand(void); |
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71 | * |
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72 | * DESCRIPTION |
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73 | * |
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74 | * The routine rng_create_rand creates and initializes a pseudo-random |
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75 | * number generator. |
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76 | * |
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77 | * RETURNS |
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78 | * |
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79 | * The routine returns a pointer to the generator created. */ |
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80 | |
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81 | RNG *rng_create_rand(void) |
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82 | { RNG *rand; |
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83 | int i; |
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84 | rand = xmalloc(sizeof(RNG)); |
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85 | A[0] = -1; |
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86 | for (i = 1; i <= 55; i++) A[i] = 0; |
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87 | fptr = A; |
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88 | rng_init_rand(rand, 1); |
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89 | return rand; |
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90 | } |
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91 | |
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92 | /*********************************************************************** |
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93 | * NAME |
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94 | * |
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95 | * rng_init_rand - initialize pseudo-random number generator |
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96 | * |
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97 | * SYNOPSIS |
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98 | * |
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99 | * #include "glprng.h" |
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100 | * void rng_init_rand(RNG *rand, int seed); |
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101 | * |
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102 | * DESCRIPTION |
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103 | * |
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104 | * The routine rng_init_rand initializes the pseudo-random number |
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105 | * generator. The parameter seed may be any integer number. Note that |
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106 | * on creating the generator this routine is called with the parameter |
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107 | * seed equal to 1. */ |
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108 | |
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109 | void rng_init_rand(RNG *rand, int seed) |
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110 | { int i; |
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111 | int prev = seed, next = 1; |
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112 | seed = prev = mod_diff(prev, 0); |
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113 | A[55] = prev; |
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114 | for (i = 21; i; i = (i + 21) % 55) |
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115 | { A[i] = next; |
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116 | next = mod_diff(prev, next); |
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117 | if (seed & 1) |
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118 | seed = 0x40000000 + (seed >> 1); |
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119 | else |
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120 | seed >>= 1; |
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121 | next = mod_diff(next, seed); |
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122 | prev = A[i]; |
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123 | } |
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124 | flip_cycle(rand); |
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125 | flip_cycle(rand); |
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126 | flip_cycle(rand); |
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127 | flip_cycle(rand); |
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128 | flip_cycle(rand); |
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129 | return; |
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130 | } |
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131 | |
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132 | /*********************************************************************** |
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133 | * NAME |
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134 | * |
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135 | * rng_next_rand - obtain pseudo-random integer in the range [0, 2^31-1] |
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136 | * |
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137 | * SYNOPSIS |
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138 | * |
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139 | * #include "glprng.h" |
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140 | * int rng_next_rand(RNG *rand); |
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141 | * |
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142 | * RETURNS |
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143 | * |
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144 | * The routine rng_next_rand returns a next pseudo-random integer which |
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145 | * is uniformly distributed between 0 and 2^31-1, inclusive. The period |
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146 | * length of the generated numbers is 2^85 - 2^30. The low order bits of |
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147 | * the generated numbers are just as random as the high-order bits. */ |
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148 | |
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149 | int rng_next_rand(RNG *rand) |
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150 | { return |
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151 | *fptr >= 0 ? *fptr-- : flip_cycle(rand); |
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152 | } |
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153 | |
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154 | /*********************************************************************** |
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155 | * NAME |
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156 | * |
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157 | * rng_unif_rand - obtain pseudo-random integer in the range [0, m-1] |
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158 | * |
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159 | * SYNOPSIS |
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160 | * |
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161 | * #include "glprng.h" |
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162 | * int rng_unif_rand(RNG *rand, int m); |
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163 | * |
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164 | * RETURNS |
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165 | * |
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166 | * The routine rng_unif_rand returns a next pseudo-random integer which |
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167 | * is uniformly distributed between 0 and m-1, inclusive, where m is any |
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168 | * positive integer less than 2^31. */ |
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169 | |
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170 | #define two_to_the_31 ((unsigned int)0x80000000) |
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171 | |
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172 | int rng_unif_rand(RNG *rand, int m) |
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173 | { unsigned int t = two_to_the_31 - (two_to_the_31 % m); |
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174 | int r; |
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175 | xassert(m > 0); |
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176 | do { r = rng_next_rand(rand); } while (t <= (unsigned int)r); |
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177 | return r % m; |
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178 | } |
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179 | |
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180 | /*********************************************************************** |
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181 | * NAME |
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182 | * |
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183 | * rng_delete_rand - delete pseudo-random number generator |
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184 | * |
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185 | * SYNOPSIS |
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186 | * |
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187 | * #include "glprng.h" |
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188 | * void rng_delete_rand(RNG *rand); |
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189 | * |
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190 | * DESCRIPTION |
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191 | * |
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192 | * The routine rng_delete_rand frees all the memory allocated to the |
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193 | * specified pseudo-random number generator. */ |
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194 | |
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195 | void rng_delete_rand(RNG *rand) |
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196 | { xfree(rand); |
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197 | return; |
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198 | } |
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199 | |
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200 | /**********************************************************************/ |
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201 | |
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202 | #if 0 |
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203 | /* To be sure that this modified version produces the same results as |
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204 | the original version, run this validation program. */ |
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205 | |
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206 | int main(void) |
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207 | { RNG *rand; |
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208 | int j; |
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209 | rand = rng_create_rand(); |
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210 | rng_init_rand(rand, -314159); |
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211 | if (rng_next_rand(rand) != 119318998) |
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212 | { fprintf(stderr, "Failure on the first try!\n"); |
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213 | return -1; |
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214 | } |
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215 | for (j = 1; j <= 133; j++) rng_next_rand(rand); |
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216 | if (rng_unif_rand(rand, 0x55555555) != 748103812) |
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217 | { fprintf(stderr, "Failure on the second try!\n"); |
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218 | return -2; |
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219 | } |
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220 | fprintf(stderr, "OK, the random-number generator routines seem to" |
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221 | " work!\n"); |
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222 | rng_delete_rand(rand); |
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223 | return 0; |
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224 | } |
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225 | #endif |
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226 | |
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227 | /* eof */ |
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