int Ray::tail(xorshift64& rand){
double x,y,r;
r = xsigma/sigma;
for(;;){
x = rand_exp(rand,r);
y = rand_exp(rand,1);
if(2*y > x*x)
break;
}
x = x*sigma+xsigma;
x = floor(x+0.5);
return int(x);
}
value gamma_CAML_randexp( value m )
{
CAMLparam1( m );
CAMLlocal1( r );
r = caml_copy_double( rand_exp( Double_val(m) ) );
CAMLreturn( r );
}
int rand_poisson
( double lambda
)
{ int v;
if (lambda>10000)
{ v = (int) (lambda + rand_gaussian()*sqrt(lambda) + 0.5);
}
else
{ v = 0;
for (;;)
{ lambda -= rand_exp();
if (lambda<=0) break;
v += 1;
}
}
return v;
}
double rand_gamma
( double a
)
{
double b, c, X, Y, Z, U, V, W;
if (a<0.00001)
{ X = a;
}
else if (a<=1)
{
U = rand_uniopen();
X = rand_gamma(1+a) * pow(U,1/a);
}
else if (a<1.00001)
{ X = rand_exp();
}
else
{
b = a-1;
c = 3*a - 0.75;
for (;;)
{
U = rand_uniopen();
V = rand_uniopen();
W = U*(1-U);
Y = sqrt(c/W) * (U-0.5);
X = b+Y;
if (X>=0)
{
Z = 64*W*W*W*V*V;
if (Z <= 1 - 2*Y*Y/X || log(Z) <= 2 * (b*log(X/b) - Y)) break;
}
}
}
return X<1e-30 && X<a ? (a<1e-30 ? a : 1e-30) : X;
}
double rexp_inv(void) {
double x = rand_exp(rng);
return exp(-x);
}
