double rnormal01(void)
{
static char f = 1;
static double y;
double a, b, s;
double mean = 0;
double sd = 1;
/* negate the flag */
f = -f;
/* return the stored number (if one is there) */
if (f > 0) return y;
for (;;)
{
a = 2.0 * dr250() - 1.0;
b = 2.0 * dr250() - 1.0;
s = a * a + b * b;
if ((s < 1.0) && (s != 0)) break;
}
s = sqrt(-2.0 * log(s) / s);
// save one of the numbers for the next time
y = sd * s * a + mean;
// and return the other
return sd * s*b + mean;
}
/*
http://www.taygeta.com/random/gaussian.html
*/
double get_gaussian_noise(void) {
double x1;
static int nb_call = 0;
static double x2, w;
if (nb_call==0) r250_init(0);
nb_call++;
if (nb_call%2) {
do {
x1 = 2.0 * dr250() - 1.0;
x2 = 2.0 * dr250() - 1.0;
w = x1 * x1 + x2 * x2;
} while ( w >= 1.0 );
w = sqrt( (-2.0 * log( w ) ) / w );
return x1 * w;
}
else
return x2 * w;
}
/*---------------------------------------------------------------------------*/
double rnd(void)
{
return dr250();
}
