gnu/lib/libg++/libg++/MLCG.cc

// This may look like C code, but it is really -*- C++ -*-
/*
Copyright (C) 1989 Free Software Foundation

This file is part of the GNU C++ Library.  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, 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#ifdef __GNUG__
#pragma implementation
#endif
#include <MLCG.h>
//
//      SEED_TABLE_SIZE must be a power of 2
//


#define SEED_TABLE_SIZE 32

static long seedTable[SEED_TABLE_SIZE] = {
0xbdcc47e5, 0x54aea45d, 0xec0df859, 0xda84637b,
0xc8c6cb4f, 0x35574b01, 0x28260b7d, 0x0d07fdbf,
0x9faaeeb0, 0x613dd169, 0x5ce2d818, 0x85b9e706,
0xab2469db, 0xda02b0dc, 0x45c60d6e, 0xffe49d10,
0x7224fea3, 0xf9684fc9, 0xfc7ee074, 0x326ce92a,
0x366d13b5, 0x17aaa731, 0xeb83a675, 0x7781cb32,
0x4ec7c92d, 0x7f187521, 0x2cf346b4, 0xad13310f,
0xb89cff2b, 0x12164de1, 0xa865168d, 0x32b56cdf
};

MLCG::MLCG(long seed1, long seed2)
{
    initialSeedOne = seed1;
    initialSeedTwo = seed2;
    reset();
}

void
MLCG::reset()
{
    long seed1 = initialSeedOne;
    long seed2 = initialSeedTwo;

    //
    //  Most people pick stupid seed numbers that do not have enough
    //  bits. In this case, if they pick a small seed number, we
    //  map that to a specific seed.
    //
    if (seed1 < 0) {
        seed1 = (seed1 + 2147483561);
        seed1 = (seed1 < 0) ? -seed1 : seed1;
    }

    if (seed2 < 0) {
        seed2 = (seed2 + 2147483561);
        seed2 = (seed2 < 0) ? -seed2 : seed2;
    }

    if (seed1 > -1 && seed1 < SEED_TABLE_SIZE) {
        seedOne = seedTable[seed1];
    } else {
        seedOne = seed1 ^ seedTable[seed1 & (SEED_TABLE_SIZE-1)];
    }

    if (seed2 > -1 && seed2 < SEED_TABLE_SIZE) {
        seedTwo = seedTable[seed2];
    } else {
        seedTwo = seed2 ^ seedTable[ seed2 & (SEED_TABLE_SIZE-1) ];
    }
    seedOne = (seedOne % 2147483561) + 1;
    seedTwo = (seedTwo % 2147483397) + 1;
}

unsigned long MLCG::asLong()
{
    long k = seedOne % 53668;

    seedOne = 40014 * (seedOne-k * 53668) - k * 12211;
    if (seedOne < 0) {
        seedOne += 2147483563;
    }

    k = seedTwo % 52774;
    seedTwo = 40692 * (seedTwo - k * 52774) - k * 3791;
    if (seedTwo < 0) {
        seedTwo += 2147483399;
    }

    long z = seedOne - seedTwo;
    if (z < 1) {
        z += 2147483562;
    }
    return( (unsigned long) z);
}