function diracDelta( x ) {
	if ( isnan( x ) ) {
		return NaN;
	}
	if ( x === 0.0 ) {
		return PINF;
	}
	return 0.0;
}
Evaluates the Dirac delta function.

@param {number} x - input value
@returns {number} function value

@example
var v = diracDelta( 0.0 );
// returns Infinity

@example
var v = diracDelta( 3.14 );
// returns 0.0

@example
var v = diracDelta( NaN );
// returns NaN