/* 
   A C-program for MT19937, with initialization improved 2002/1/26.
   Coded by Takuji Nishimura and Makoto Matsumoto.

   Before using, initialize the state by using init_genrand(seed)  
   or init_by_array(init_key, key_length).

   Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
   All rights reserved.                          

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions
   are met:

     1. Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.

     2. Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in the
        documentation and/or other materials provided with the distribution.

     3. The names of its contributors may not be used to endorse or promote 
        products derived from this software without specific prior written 
        permission.

   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


   Any feedback is very welcome.
   http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
   email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space)
*/

#include "mt19937ar.h"

#include <stdlib.h>
#include <math.h>


//  Buried in genrand_in32 was this:
//    if init_genrand() has not been called,
//    a default initial seed is used
//
//    if (ctx->mti == N+1)
//      init_genrand(5489UL);
//
//  But we don't need that anymore, as we require for
//  thread-safety that init_genrand be called.




//  initialize with a single seed
mt_s*
mtInit(u32bit s) {
  mt_s *ctx = (mt_s *)malloc(sizeof(mt_s));
  if (ctx == NULL)
    return(NULL);

  ctx->mt[0] = s;

  // See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier.
  // In the previous versions, MSBs of the seed affect
  // only MSBs of the array mt[].
  // 2002/01/09 modified by Makoto Matsumoto

  for (ctx->mti=1; ctx->mti<MT_N; ctx->mti++)
    ctx->mt[ctx->mti] = (1812433253UL * (ctx->mt[ctx->mti-1] ^ (ctx->mt[ctx->mti-1] >> 30)) + ctx->mti); 

  ctx->mag01[0] = u32bitZERO;
  ctx->mag01[1] = MT_MATRIX_A;

  return(ctx);
}




/* initialize by an array with array-length */
/* init_key is the array for initializing keys */
/* key_length is its length */
/* slight change for C++, 2004/2/26 */
mt_s*
mtInitArray(u32bit *init_key, u32bit key_length) {

  mt_s *ctx = mtInit(19650218UL);
  int   i   = 1;
  int   j   = 0;
  int   k   = (MT_N > key_length ? MT_N : key_length);

  for (; k; k--) {
    ctx->mt[i] = (ctx->mt[i] ^ ((ctx->mt[i-1] ^ (ctx->mt[i-1] >> 30)) * 1664525UL)) + init_key[j] + j; /* non linear */
    i++;
    j++;
    if (i >= MT_N) {
      ctx->mt[0] = ctx->mt[MT_N-1];
      i=1;
    }
    if (j >= key_length)
      j=0;
  }
  for (k=MT_N-1; k; k--) {
    ctx->mt[i] = (ctx->mt[i] ^ ((ctx->mt[i-1] ^ (ctx->mt[i-1] >> 30)) * 1566083941UL)) - i; /* non linear */
    i++;
    if (i>=MT_N) {
      ctx->mt[0] = ctx->mt[MT_N-1];
      i=1;
    }
  }

  ctx->mt[0] = 0x80000000UL; /* MSB is 1; assuring non-zero initial array */ 
  return(ctx);
}



/* generates a random number on [0,0xffffffff]-interval */
u32bit
mtRandom32(mt_s *ctx) {
    u32bit y;

    //  generate MT_N words at one time
    //
    if (ctx->mti >= MT_N) {
        int kk;

        for (kk=0; kk < MT_N - MT_M; kk++) {
            y = (ctx->mt[kk] & MT_UPPER_MASK) | (ctx->mt[kk+1] & MT_LOWER_MASK);
            ctx->mt[kk] = ctx->mt[kk + MT_M] ^ (y >> 1) ^ ctx->mag01[y & u32bitONE];
        }
        for (; kk < MT_N-1; kk++) {
            y = (ctx->mt[kk] & MT_UPPER_MASK) | (ctx->mt[kk + 1] & MT_LOWER_MASK);
            ctx->mt[kk] = ctx->mt[kk + (MT_M - MT_N)] ^ (y >> 1) ^ ctx->mag01[y & u32bitONE];
        }
        y = (ctx->mt[MT_N-1] & MT_UPPER_MASK) | (ctx->mt[0] & MT_LOWER_MASK);
        ctx->mt[MT_N-1] = ctx->mt[MT_M-1] ^ (y >> 1) ^ ctx->mag01[y & u32bitONE];

        ctx->mti = 0;
    }

    y = ctx->mt[ctx->mti++];

    /* Tempering */
    y ^= (y >> 11);
    y ^= (y << 7) & 0x9d2c5680UL;
    y ^= (y << 15) & 0xefc60000UL;
    y ^= (y >> 18);

    return y;
}


//  generates a random number on gaussian distribution with 0 median and 1 std.dev.
double
mtRandomGaussian(mt_s *mt) {
  double  x1=0, x2=0, w=0, y1=0, y2=0;

  //  from http://www.taygeta.com/random/gaussian.html
  //
  //  supposedly equivalent to
  //
  //  y1 = sqrt(-2*ln(x1)) cos(2*pi*x2)
  //  y2 = sqrt(-2*ln(x1)) sin(2*pi*x2)
  //
  //  but stable when x1 close to zero

  do {
    x1 = 2.0 * mtRandomRealClosed(mt) - 1.0;
    x2 = 2.0 * mtRandomRealClosed(mt) - 1.0;
    w = x1 * x1 + x2 * x2;
  } while (w >= 1.0);

  w = sqrt( (-2.0 * log(w)) / w);

  y1 = x1 * w;
  y2 = x2 * w;

  return(y1);
}
