function exponent( x ) {
	return addon( x );
}
Returns an integer corresponding to the unbiased exponent of a double-precision floating-point number.

@private
@param {number} x - input value
@returns {integer32} unbiased exponent

@example
var exp = exponent( 3.14e-307 ); // => 2**-1019 ~ 1e-307
// returns -1019

@example
var exp = exponent( -3.14 );
// returns 1

@example
var exp = exponent( 0.0 );
// returns -1023

@example
var exp = exponent( NaN );
// returns 1024