function pdifff( x, y ) {
	if ( isnanf( x ) || isnanf( y ) ) {
		return NaN;
	}
	if ( x > y ) {
		return float64ToFloat32( float64ToFloat32(x) - float64ToFloat32(y) );
	}
	return 0.0;
}
Returns the positive difference between `x` and `y` if `x > y`; otherwise, returns `0`.

@param {number} x - first number
@param {number} y - second number
@returns {number} positive difference

@example
var v = pdifff( 5.9, 3.15 );
// returns 2.75

@example
var v = pdifff( 3.14, 4.2 );
// returns 0.0

@example
var v = pdifff( 3.14, NaN );
// returns NaN

@example
var v = pdifff( -0.0, +0.0 );
// returns +0.0