/*
 *
 * Copyright (C) 2010 - DIGITEO - Michael Baudin
 * Copyright (C) 2004 - Bruno Pincon
 * Copyright (C) Luc Devroye
 * Copyright (C) Pierre Lecuyer
 *
 *  PURPOSE
 *     uniform random number generator developed by Pierre
 *     Lecuyer based on a clever and tested combination of
 *     two linear congruential sequences
 *
 *        s1 <- a1*s1 mod m1 ,  a1 = 40014, m1 = 2147483563
 *        s2 <- a2*s2 mod m2 ,  a2 = 40692, m2 = 2147483399
 *
 *        output <-  s1-s2 mod (m1 - 1)
 *
 *        so output is in [0, 2147483561], period about 2.3 10^18
 *
 *        The state is given by (s1, s2). In case of a user
 *        modification of the state we must have :
 *
 *              s1 in [1, m1-1]
 *              s2 in [1, m2-1]
 *
 *  ORIGIN
 *     The basic code is provided at the Luc Devroye 's home page.
 *     Modifications by Bruno Pincon (in particular added routines
 *     to set and get the state, and modify the generator to get
 *     exactly  s1-s2 mod (m1 - 1) for "coherence" with the others
 *     generators : provides numbers in [0, MaxRngInt(generator)]
 *     (see NOTE some lines after)
 *
 */

#include <math.h>
#include "localization.h"
#include "sciprint.h"
#include "others_generators.h"

/* initial default state (seeds) : */
static int s1 = 1234567890 ;
static int s2 = 123456789  ;

unsigned long int clcg2(void)
{
    register int k, z;

    /*  s1 = a1*s1 mod m1  (Schrage 's method)  */
    k = s1 / 53668;
    s1 = 40014 * (s1 % 53668) - k * 12211;
    if (s1 < 0)
    {
        s1 += 2147483563;
    }

    /*  s2 = a2*s2 mod m2  (Schrage 's method)  */
    k = s2 / 52774;
    s2 = 40692 * (s2 % 52774) - k * 3791;
    if (s2 < 0)
    {
        s2 += 2147483399;
    }

    /* final step : z = s1-s2 mod m1-1  */
    z = s1 - s2;  /* here z is in [2-m2,m1-2] */
    if (z < 0)
    {
        z += 2147483562;
    }

    /* NOTE : in the  original implementation the final test is :
    *     if (z < 1) z += 2147483562;
    *
    *   which is not exactly  z = s1-s2 mod (m1 - 1)
    *
    *   This is also why it is different from the version used by
    *   randlib.
    */

    return( (unsigned int) z );
}

int set_state_clcg2(double g1, double g2)
{

    if ( g1 == floor(g1) && g2 == floor(g2)  &&
            1 <= g1 && g1 <= 2147483562    &&
            1 <= g2 && g2 <= 2147483398 )
    {
        s1 = (int) g1;
        s2 = (int) g2;
        return ( 1 );
    }
    else
    {
        sciprint(_("\nBad seeds for clcg2, must be integers with  s1 in [1, 2147483562]\n                                        and  s2 in [1, 2147483398]\n"));
        return ( 0 );
    }
}

void get_state_clcg2(double g[])
{
    g[0] = (double) s1;
    g[1] = (double) s2;
}

