/// <summary>
/// Sample from the distribution tail (defined as having x >= __R).
/// </summary>
/// <returns>A new random sample from the Gaussian distribution tail.</returns>
private static float SampleTail(IRandomSource rng)
{
float x, y;
do
{
// Note. we use NextFloatNonZero() because Log(0) returns -Infinity and will also tend to be a very slow execution path (when it occurs, which is rarely).
x = -MathF.Log(rng.NextFloatNonZero()) / __RF;
y = -MathF.Log(rng.NextFloatNonZero());
}while(y + y < x * x);
return(__RF + x);
}