/*
 *      drand48, etc. pseudo-random number generator
 *      This implementation assumes unsigned short integers of at least
 *      16 bits, long integers of at least 32 bits, and ignores
 *      overflows on adding or multiplying two unsigned integers.
 *      Two's-complement representation is assumed in a few places.
 *      Some extra masking is done if unsigneds are exactly 16 bits
 *      or longs are exactly 32 bits, but so what?
 *      An assembly-language implementation would run significantly faster.
 */

#if !defined (WINNT) && !defined (MAC_OSX)

int drand48Dummy()
{
    return( 0 );
}

#else

#ifndef HAVEFP
#define HAVEFP 1
#endif

#define N       16
#define MASK    ((unsigned)(1 << (N - 1)) + (1 << (N - 1)) - 1)
#define LOW(x)  ((unsigned)(x) & MASK)
#define HIGH(x) LOW((x) >> N)

#define CARRY(x, y)     ((long)(x) + (long)(y) > MASK)
#define ADDEQU(x, y, z) (z = CARRY(x, (y)), x = LOW(x + (y)))

#define MUL(x, y, z)    { long l = (long)(x) * (long)(y); \
                        (z)[0] = LOW(l); (z)[1] = HIGH(l); }

#define X0      0x330E
#define X1      0xABCD
#define X2      0x1234
#define A0      0xE66D
#define A1      0xDEEC
#define A2      0x5
#define C       0xB

#define SET3(x, x0, x1, x2)     ((x)[0] = (x0), (x)[1] = (x1), (x)[2] = (x2))
#define SETLOW(x, y, n) SET3(x, LOW((y)[n]), LOW((y)[(n)+1]), LOW((y)[(n)+2]))
#define SEED(x0, x1, x2) (SET3(x, x0, x1, x2), SET3(a, A0, A1, A2), c = C)

#define REST(v) for (i = 0; i < 3; i++) \
                { xsubi[i] = x[i]; x[i] = temp[i]; } \
                return (v);

#define NEST(TYPE, f, F) \
        TYPE f(xsubi) register unsigned short *xsubi; { \
        register int i; register TYPE v; unsigned temp[3]; \
        for (i = 0; i < 3; i++) { temp[i] = x[i]; x[i] = LOW(xsubi[i]); }  \
        v = F(); REST(v); }

#define HI_BIT  (1L << (2 * N - 1))

static unsigned x[3] = { X0, X1, X2 }, a[3] = { A0, A1, A2 }, c = C;
static unsigned short lastx[3];
static void next();

#if HAVEFP
double drand48()
{
        static double two16m = 1.0 / (1L << N);
        next();
        return (two16m * (two16m * (two16m * x[0] + x[1]) + x[2]));
}

NEST(double, erand48, drand48);

#else

long irand48(m)

/* Treat x[i] as a 48-bit fraction, and multiply it by the 16-bit
 * multiplier m.  Return integer part as result.
 */
register unsigned short m;
{
        unsigned r[4], p[2], carry0 = 0;

        next();
        MUL(m, x[0], &r[0]);
        MUL(m, x[2], &r[2]);
        MUL(m, x[1], p);
        if (CARRY(r[1], p[0]))
                ADDEQU(r[2], 1, carry0);
        return (r[3] + carry0 + CARRY(r[2], p[1]));
}

long krand48(xsubi, m)

/* same as irand48, except user provides storage in xsubi[] */
register unsigned short *xsubi;
unsigned short m;
{
        register int i;
        register long iv;
        unsigned temp[3];

        for (i = 0; i < 3; i++) {
                temp[i] = x[i];
                x[i] = xsubi[i];
        }
        iv = irand48(m);
        REST(iv);
}
#endif

long lrand48()
{
        next();
        return (((long)x[2] << (N - 1)) + (x[1] >> 1));
}

long mrand48()
{
        register long l;

        next();
        /* sign-extend in case length of a long > 32 bits
                                                (as on Honeywell) */
        return ((l = ((long)x[2] << N) + x[1]) & HI_BIT ? l | -HI_BIT : l);
}

static void next()
{
        unsigned p[2], q[2], r[2], carry0, carry1;

        MUL(a[0], x[0], p);
        ADDEQU(p[0], c, carry0);
        ADDEQU(p[1], carry0, carry1);
        MUL(a[0], x[1], q);
        ADDEQU(p[1], q[0], carry0);
        MUL(a[1], x[0], r);
        x[2] = LOW(carry0 + carry1 + CARRY(p[1], r[0]) + q[1] + r[1] +
                a[0] * x[2] + a[1] * x[1] + a[2] * x[0]);
        x[1] = LOW(p[1] + r[0]);
        x[0] = LOW(p[0]);
}

void srand48(seedval)
long seedval;
{
        SEED(X0, LOW(seedval), HIGH(seedval));
}

unsigned short *seed48(seed16v)
unsigned short seed16v[3];
{
        SETLOW(lastx, x, 0);
        SEED(LOW(seed16v[0]), LOW(seed16v[1]), LOW(seed16v[2]));
        return (lastx);
}

void lcong48(param)
unsigned short param[7];
{
        SETLOW(x, param, 0);
        SETLOW(a, param, 3);
        c = LOW(param[6]);
}

NEST(long, nrand48, lrand48);
NEST(long, jrand48, mrand48);

#ifdef DRIVER
/*
        This should print the sequences of integers in Tables 2
                and 1 of the TM:
        1623, 3442, 1447, 1829, 1305, ...
        657EB7255101, D72A0C966378, 5A743C062A23, ...
*/

#include <stdio.h>

int main()
{
    int i;

    for( i = 0; i < 80; i++ )
       {
        (void) printf( "%4d ", (int)(4096*drand48()) );
        (void) printf( "%.4X%.4X%.4X\n", x[2], x[1], x[0] );
       }

    return( 0 );
}

#endif
#endif