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  1. /*
  2.    Copyright (C) 1997--2004, Makoto Matsumoto, Takuji Nishimura, and
  3.    Eric Landry; All rights reserved.
  4.  
  5.    Redistribution and use in source and binary forms, with or without
  6.    modification, are permitted provided that the following conditions
  7.    are met:
  8.  
  9.      1. Redistributions of source code must retain the above copyright
  10.         notice, this list of conditions and the following disclaimer.
  11.  
  12.      2. Redistributions in binary form must reproduce the above copyright
  13.         notice, this list of conditions and the following disclaimer
  14.         in the documentation and/or other materials provided with the
  15.         distribution.
  16.  
  17.      3. The names of its contributors may not be used to endorse or
  18.         promote products derived from this software without specific
  19.         prior written permission.
  20.  
  21.    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22.    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23.    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  24.    A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT
  25.    OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  26.    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  27.    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  28.    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  29.    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  30.    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  31.    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  32.  
  33.    Any feedback is very welcome.
  34.    http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
  35.    email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space)
  36.  
  37.    Reference: M. Matsumoto and T. Nishimura, "Mersenne Twister:
  38.    A 623-Dimensionally Equidistributed Uniform Pseudo-Random Number
  39.    Generator", ACM Transactions on Modeling and Computer Simulation,
  40.    Vol. 8, No. 1, January 1998, pp 3--30.
  41. */
  42.  
  43. #include "mtrand.h"
  44.  
  45. /* Period parameters */
  46. #define N 624
  47. #define M 397
  48. #define MATRIX_A 0x9908b0dfUL   /* constant vector a */
  49. #define UPPER_MASK 0x80000000UL /* most significant w-r bits */
  50. #define LOWER_MASK 0x7fffffffUL /* least significant r bits */
  51.  
  52. static unsigned long x[N];      /* the array for the state vector  */
  53. static unsigned long *p0, *p1, *pm;
  54.  
  55. void mt_srand( unsigned long s )
  56. {
  57.         int i;
  58.        
  59.         x[0] = s & 0xffffffffUL;
  60.         for (i = 1; i < N; ++i) {
  61.                 x[i] = (1812433253UL * (x[i - 1] ^ (x[i - 1] >> 30)) + i)
  62.                      & 0xffffffffUL;           /* for >32 bit machines */
  63.         }
  64.         p0 = x;
  65.         p1 = x + 1;
  66.         pm = x + M;
  67. }
  68.  
  69. /* generates a random number on the interval [0,0xffffffff] */
  70. unsigned long mt_rand( void )
  71. {
  72.         unsigned long y;
  73.  
  74.         if (!p0) {
  75.                 /* Default seed */
  76.                 mt_srand(5489UL);
  77.         }
  78.         /* Twisted feedback */
  79.         y = *p0 = *pm++ ^ (((*p0 & UPPER_MASK) | (*p1 & LOWER_MASK)) >> 1) ^ ((~(*p1 & 1)+1) & MATRIX_A);
  80.         p0 = p1++;
  81.         if (pm == x + N) {
  82.                 pm = x;
  83.         }
  84.         if (p1 == x + N) {
  85.                 p1 = x;
  86.         }
  87.         /* Temper */
  88.         y ^= y >> 11;
  89.         y ^= y << 7 & 0x9d2c5680UL;
  90.         y ^= y << 15 & 0xefc60000UL;
  91.         y ^= y >> 18;
  92.         return y;
  93. }
  94.  
  95. /* generates a random number on the interval [0,1]. */
  96. float mt_rand_1( void )
  97. {
  98.         return ((float)mt_rand() / (float)MT_RAND_MAX);
  99. }
  100.  
  101. /* generates a random number on the interval [0,1). */
  102. float mt_rand_lt1( void )
  103. {
  104.         /* MT_RAND_MAX must be a float before adding one to it! */
  105.         return ((float)mt_rand() / ((float)MT_RAND_MAX + 1.0f));
  106. }
  107.  
  108.