/* RAND functions using 64b INTEGERs
F. CANTONNET - HPCL - GWU */
double randlc (double *x, double a)
{
/* This routine returns a uniform pseudorandom double precision number in the
range (0, 1) by using the linear congruential generator
x_{k+1} = a x_k (mod 2^46)
where 0 < x_k < 2^46 and 0 < a < 2^46. This scheme generates 2^44 numbers
before repeating. The argument A is the same as 'a' in the above formula,
and X is the same as x_0. A and X must be odd double precision integers
in the range (1, 2^46). The returned value RANDLC is normalized to be
between 0 and 1, i.e. RANDLC = 2^(-46) * x_1. X is updated to contain
the new seed x_1, so that subsequent calls to RANDLC using the same
arguments will generate a continuous sequence.
This routine should produce the same results on any computer with at least
48 mantissa bits in double precision floating point data. On 64 bit
systems, double precision should be disabled.
David H. Bailey October 26, 1990 */
unsigned long long i246m1, Lx, La;
double d2m46;
d2m46 = 0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*
0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*
0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*
0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*
0.5*0.5*0.5*0.5*0.5*0.5;
//d2m46 = pow( 0.5, 46 );
i246m1 = 0x00003FFFFFFFFFFFLL;
Lx = *x;
La = a;
Lx = (Lx*La)&i246m1;
*x = (double) Lx;
return (d2m46 * (*x));
}
void vranlc (int n, double *x_seed, double a, double y[]) {
/* This routine generates N uniform pseudorandom double precision numbers in
the range (0, 1) by using the linear congruential generator
x_{k+1} = a x_k (mod 2^46)
where 0 < x_k < 2^46 and 0 < a < 2^46. This scheme generates 2^44 numbers
before repeating. The argument A is the same as 'a' in the above formula,
and X is the same as x_0. A and X must be odd double precision integers
in the range (1, 2^46). The N results are placed in Y and are normalized
to be between 0 and 1. X is updated to contain the new seed, so that
subsequent calls to VRANLC using the same arguments will generate a
continuous sequence. If N is zero, only initialization is performed, and
the variables X, A and Y are ignored.
This routine is the standard version designed for scalar or RISC systems.
However, it should produce the same results on any single processor
computer with at least 48 mantissa bits in double precision floating point
data. On 64 bit systems, double precision should be disabled.
*/
int i;
double x;
unsigned long long i246m1, Lx, La;
double d2m46;
d2m46 = 0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*
0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*
0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*
0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*
0.5*0.5*0.5*0.5*0.5*0.5;
// d2m46 = pow( 0.5, 46.0 );
i246m1 = 0x00003FFFFFFFFFFFLL;
x = *x_seed;
Lx = x;
La = a;
for (i = 1; i <= n; i++)
{
Lx = ((Lx*La)&i246m1);
x = (double) Lx;
y[i] = d2m46 * x;
}
*x_seed = x;
}