function modf( x ) {
	var out = new Float64Array( 2 );
	addon( x, out );
	return out;
}
Decomposes a double-precision floating-point number into integral and fractional parts, each having the same type and sign as the input value.

@private
@param {number} x - input value
@returns {Float64Array} output array

@example
var parts = modf( 3.14 );
// returns <Float64Array>[ 3.0, 0.14000000000000012 ]