function quantile( r ) {
		var guess;
		var corr;
		var x2;
		var x;

		if ( isnan( r ) || r < 0.0 || r > 1.0 ) {
			return NaN;
		}
		if ( r === 0.0 ) {
			return 0;
		}
		if ( r === 1.0 ) {
			return n;
		}
		// Cornish-Fisher expansion:
		if ( r < 0.5 ) {
			x = -erfcinv( 2.0 * r ) * SQRT2;
		} else {
			x = erfcinv( 2.0 * ( 1.0-r ) ) * SQRT2;
		}
		x2 = x * x;

		// Skewness correction:
		corr = x + ( sigmaInv * ( x2-1.0 ) / 6.0 );
		guess = round( mu + (sigma * corr) );
		if ( cdf( guess, n, p ) >= r ) {
			return searchLeft( guess, r, n, p );
		}
		return searchRight( guess, r, n, p );
	}
Evaluates the quantile function for a binomial distribution.

@private
@param {Probability} r - input value
@returns {NonNegativeInteger} evaluated quantile function

@example
var y = quantile( 0.3 );
// returns <number>