// This is the ``Mersenne Twister'' random number generator MT19937, which
// generates pseudorandom integers uniformly distributed in 0..(2^32 - 1)
// starting from any odd seed in 0..(2^32 - 1).  This version is a recode
// by Shawn Cokus (Cokus@math.washington.edu) on March 8, 1998 of a version by
// Takuji Nishimura (who had suggestions from Topher Cooper and Marc Rieffel in
// July-August 1997).
//
// Effectiveness of the recoding (on Goedel2.math.washington.edu, a DEC Alpha
// running OSF/1) using GCC -O3 as a compiler: before recoding: 51.6 sec. to
// generate 300 million random numbers; after recoding: 24.0 sec. for the same
// (i.e., 46.5% of original time), so speed is now about 12.5 million random
// number generations per second on this machine.
//
// According to the URL <http://www.math.keio.ac.jp/~matumoto/emt.html>
// (and paraphrasing a bit in places), the Mersenne Twister is ``designed
// with consideration of the flaws of various existing generators,'' has
// a period of 2^19937 - 1, gives a sequence that is 623-dimensionally
// equidistributed, and ``has passed many stringent tests, including the
// die-hard test of G. Marsaglia and the load test of P. Hellekalek and
// S. Wegenkittl.''  It is efficient in memory usage (typically using 2506
// to 5012 bytes of static data, depending on data type sizes, and the code
// is quite short as well).  It generates random numbers in batches of 624
// at a time, so the caching and pipelining of modern systems is exploited.
// It is also divide- and mod-free.
//
// This library is free software; you can redistribute it and/or modify it
// under the terms of the GNU Library General Public License as published by
// the Free Software Foundation (either version 2 of the License or, at your
// option, any later version).  This library is distributed in the hope that
// it will be useful, but WITHOUT ANY WARRANTY, without even the implied
// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
// the GNU Library General Public License for more details.  You should have
// received a copy of the GNU Library General Public License along with this
// library; if not, write to the Free Software Foundation, Inc., 59 Temple
// Place, Suite 330, Boston, MA 02111-1307, USA.
//
// The code as Shawn received it included the following notice:
//
//   Copyright (C) 1997 Makoto Matsumoto and Takuji Nishimura.  When
//   you use this, send an e-mail to <matumoto@math.keio.ac.jp> with
//   an appropriate reference to your work.
//
// It would be nice to CC: <Cokus@math.washington.edu> when you write.
//
// RandMT class created by Paul Gresham <gresham@mediavisual.com>
// There seems to be a slight performance deficit in process creation
// however I've not profiled the class to compare it with the straight
// C code.
//
// Use of a class removes many C nasties and also allows you to easily
// create multiple generators.
// To compile on GNU a simple line is:
// g++ -O3 RandMT.cc -o RandMT
//

#include <iostream>
#include <cstdlib>

// To keep this all as one file (easier distribution) the class is
// in the code, cut'n'paste this bit to create a .h for use in
// other programs

#include "RandMT.h"

//using namespace std;

namespace MFM {

//
// uint32 must be an unsigned integer type capable of holding at least 32
// bits; exactly 32 should be fastest, but 64 is better on an Alpha with
// GCC at -O3 optimization so try your options and see what's best for you
//


RandMT::RandMT() {
  seedMT(1U);
}

RandMT::RandMT(uint32 seed) {
  seedMT(seed);
}

/* initializes state[N] with a seed */
void RandMT::seedMT_MFM(uint32 s)
{
    int j;
    state[0]= s & 0xffffffffUL;
    for (j=1; j<N; j++) {
        state[j] = (1812433253UL * (state[j-1] ^ (state[j-1] >> 30)) + j);
        /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
        /* In the previous versions, MSBs of the seed affect   */
        /* only MSBs of the array state[].                     */
        /* 2002/01/09 modified by Makoto Matsumoto             */
        state[j] &= 0xffffffffUL;  /* for >32 bit machines */
    }
    left = 0;

    /* ACKLEYHAX: DO SOME IMMEDIATE MIXING TO HELP BLOW OFF EARLY CRAP */
    for (j=0; j<10*N; j++)
      randomMT();
}


void RandMT::seedMT(uint32 seed) {
  //
  // We initialize state[0..(N-1)] via the generator
  //
  //   x_new = (69069 * x_old) mod 2^32
  //
  // from Line 15 of Table 1, p. 106, Sec. 3.3.4 of Knuth's
  // _The Art of Computer Programming_, Volume 2, 3rd ed.
  //
  // Notes (SJC): I do not know what the initial state requirements
  // of the Mersenne Twister are, but it seems this seeding generator
  // could be better.  It achieves the maximum period for its modulus
  // (2^30) iff x_initial is odd (p. 20-21, Sec. 3.2.1.2, Knuth); if
  // x_initial can be even, you have sequences like 0, 0, 0, ...;
  // 2^31, 2^31, 2^31, ...; 2^30, 2^30, 2^30, ...; 2^29, 2^29 + 2^31,
  // 2^29, 2^29 + 2^31, ..., etc. so I force seed to be odd below.
  //
  // Even if x_initial is odd, if x_initial is 1 mod 4 then
  //
  //   the          lowest bit of x is always 1,
  //   the  next-to-lowest bit of x is always 0,
  //   the 2nd-from-lowest bit of x alternates      ... 0 1 0 1 0 1 0 1 ... ,
  //   the 3rd-from-lowest bit of x 4-cycles        ... 0 1 1 0 0 1 1 0 ... ,
  //   the 4th-from-lowest bit of x has the 8-cycle ... 0 0 0 1 1 1 1 0 ... ,
  //    ...
  //
  // and if x_initial is 3 mod 4 then
  //
  //   the          lowest bit of x is always 1,
  //   the  next-to-lowest bit of x is always 1,
  //   the 2nd-from-lowest bit of x alternates      ... 0 1 0 1 0 1 0 1 ... ,
  //   the 3rd-from-lowest bit of x 4-cycles        ... 0 0 1 1 0 0 1 1 ... ,
  //   the 4th-from-lowest bit of x has the 8-cycle ... 0 0 1 1 1 1 0 0 ... ,
  //    ...
  //
  // The generator's potency (min. s>=0 with (69069-1)^s = 0 mod 2^32) is
  // 16, which seems to be alright by p. 25, Sec. 3.2.1.3 of Knuth.  It
  // also does well in the dimension 2..5 spectral tests, but it could be
  // better in dimension 6 (Line 15, Table 1, p. 106, Sec. 3.3.4, Knuth).
  //
  // Note that the random number user does not see the values generated
  // here directly since reloadMT() will always munge them first, so maybe
  // none of all of this matters.  In fact, the seed values made here could
  // even be extra-special desirable if the Mersenne Twister theory says
  // so-- that's why the only change I made is to restrict to odd seeds.
  //
  initseed = seed;

  register uint32 x = (seed | 1U) & 0xFFFFFFFFU, *s = state;
  register int    j;
  left = 0;
  for(*s++=x, j=N; --j; *s++ = (x*=69069U) & 0xFFFFFFFFU);
}

uint32 RandMT::reloadMT(void) {
  register uint32 *p0=state, *p2=state+2, *pM=state+M, s0, s1;
  register int    j;

  if(left < -1)
    seedMT(initseed);

  left=N-1, next=state+1;

  for(s0=state[0], s1=state[1], j=N-M+1; --j; s0=s1, s1=*p2++)
    *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);

  for(pM=state, j=M; --j; s0=s1, s1=*p2++)
    *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);

  s1=state[0], *p0 = *pM ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
  s1 ^= (s1 >> 11);
  s1 ^= (s1 <<  7) & 0x9D2C5680U;
  s1 ^= (s1 << 15) & 0xEFC60000U;
  return(s1 ^ (s1 >> 18));
}
} /* namespace MFM */
