src/base/random_mt.cc

   1 /*
   2  * A C-program for MT19937, with initialization improved 2002/1/26.
   3  * Coded by Takuji Nishimura and Makoto Matsumoto.
   4  *
   5  * Before using, initialize the state by using init_genrand(seed)
   6  * or init_by_array(init_key, key_length).
   7  *
   8  * Copyright (C) 1997-2002 Makoto Matsumoto and Takuji Nishimura
   9  * All rights reserved.
  10  *
  11  * Redistribution and use in source and binary forms, with or without
  12  * modification, are permitted provided that the following conditions
  13  * are met:
  14  *
  15  *   1. Redistributions of source code must retain the above copyright
  16  *   notice, this list of conditions and the following disclaimer.
  17  *
  18  *   2. Redistributions in binary form must reproduce the above
  19  *   copyright notice, this list of conditions and the following
  20  *   disclaimer in the documentation and/or other materials provided
  21  *   with the distribution.
  22  *
  23  *   3. The names of its contributors may not be used to endorse or
  24  *   promote products derived from this software without specific
  25  *   prior written permission.
  26  *
  27  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  28  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  29  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  30  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  31  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  32  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  33  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  34  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  36  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  37  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
  38  * OF THE POSSIBILITY OF SUCH DAMAGE.
  39  *
  40  *
  41  * Any feedback is very welcome.
  42  * http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
  43  * email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space)
  44  */
  45
  46 #include "base/random.hh"
  47
  48 /* initializes mt[N] with a seed */
  49 void
  50 Random::init(uint32_t s)
  51 {
  52     mti = N + 1;
  53     mt[0] = s & (uint32_t)0xffffffff;
  54
  55     for (mti = 1; mti < N; mti++) {
  56         mt[mti] = 1812433253UL * (mt[mti-1] ^ (mt[mti-1] >> 30)) + mti;
  57         /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
  58         /* In the previous versions, MSBs of the seed affect   */
  59         /* only MSBs of the array mt[].                        */
  60         /* 2002/01/09 modified by Makoto Matsumoto             */
  61         mt[mti] &= (uint32_t)0xffffffff;
  62         /* for >32 bit machines */
  63     }
  64 }
  65
  66 /* initialize by an array with array-length */
  67 /* init_key is the array for initializing keys */
  68 /* key_length is its length */
  69 /* slight change for C++, 2004/2/26 */
  70 void
  71 Random::init(uint32_t init_key[], int key_length)
  72 {
  73     int i = 1;
  74     int j = 0;
  75     int k = (N > key_length) ? N : key_length;
  76
  77     init(19650218);
  78
  79     for (; k; k--) {
  80         mt[i] = (mt[i] ^ ((mt[i-1] ^ (mt[i-1] >> 30)) * (uint32_t)1664525))
  81           + init_key[j] + j; /* non linear */
  82
  83         mt[i] &= 0xffffffffUL; /* for WORDSIZE > 32 machines */
  84
  85         i++;
  86         j++;
  87
  88         if (i >= N) {
  89             mt[0] = mt[N - 1];
  90             i = 1;
  91         }
  92
  93         if (j >= key_length)
  94             j = 0;
  95     }
  96
  97     for (k = N - 1; k; k--) {
  98         /* non linear */
  99         mt[i] = (mt[i] ^ ((mt[i - 1] ^ (mt[i - 1] >> 30)) * 1566083941UL)) - i;
 100
 101         /* for WORDSIZE > 32 machines */
 102         mt[i] &= (uint32_t)0xffffffff;
 103         i++;
 104
 105         if (i >= N) {
 106             mt[0] = mt[N - 1];
 107             i = 1;
 108         }
 109     }
 110
 111     /* MSB is 1; assuring non-zero initial array */
 112     mt[0] = (uint32_t)0x80000000;
 113 }
 114
 115 /* generates a random number on [0,0xffffffff]-interval */
 116 uint32_t
 117 Random::genrand()
 118 {
 119     uint32_t y;
 120     static uint32_t mag01[2] = { 0, MATRIX_A};
 121
 122     if (mti >= N) { /* generate N words at one time */
 123         int kk;
 124
 125         for (kk = 0; kk < N - M; kk++) {
 126             y = (mt[kk] & UPPER_MASK) | (mt[kk+1] & LOWER_MASK);
 127             mt[kk] = mt[kk + M] ^ (y >> 1) ^ mag01[y & 0x1UL];
 128         }
 129         for (; kk < N - 1; kk++) {
 130             y = (mt[kk] & UPPER_MASK) | (mt[kk+1] & LOWER_MASK);
 131             mt[kk] = mt[kk + (M - N)] ^ (y >> 1) ^ mag01[y & 0x1UL];
 132         }
 133
 134         y = (mt[N - 1] & UPPER_MASK) | (mt[0] & LOWER_MASK);
 135         mt[N - 1] = mt[M - 1] ^ (y >> 1) ^ mag01[y & 0x1UL];
 136
 137         mti = 0;
 138     }
 139
 140     y = mt[mti++];
 141
 142     /* Tempering */
 143     y ^= (y >> 11);
 144     y ^= (y << 7) & (uint32_t)0x9d2c5680;
 145     y ^= (y << 15) & (uint32_t)0xefc60000;
 146     y ^= (y >> 18);
 147
 148     return y;
 149 }