function sample( randu, randn, alpha ) {
	var flg;
	var s4;
	var A;
	var s;
	var t;
	var u;
	var x;
	var y;

	A = alpha - 1.0;
	t = pow( A+A, 0.5 );

	flg = true;
	while ( flg === true ) {
		s = randn();
		x = 0.5 * ( 1.0+(s/t) );
		if ( x >= 0.0 && x <= 1.0 ) {
			u = randu();
			s4 = pow( s, 4.0 );
			y = (8.0*alpha) - 12.0;
			y = 1.0 - (s4 / y);
			if ( u <= y ) {
				flg = false;
			} else {
				y += 0.5 * pow( s4/((8.0*alpha)-8.0), 2.0 );
				if ( u < y ) {
					y = A * ln( 4.0*x*(1.0-x) );
					y += s*s / 2.0;
					if ( y >= ln( u ) ) {
						flg = false;
					}
				}
			}
		}
	}
	return x;
}
Handles case where `alpha` and `beta` are equal and greater than `1.5`.

@private
@param {PRNG} randu - PRNG for uniformly distributed numbers
@param {PRNG} randn - PRNG for normally distributed numbers
@param {PositiveNumber} alpha - first shape parameter
@returns {Probability} pseudorandom number