function log1pmx( x ) {
	var opts;
	var ax;
	if ( x <= -1.0 ) {
		return NaN;
	}
	ax = abs( x );
	if ( ax > 0.95 ) {
		return ln( 1.0 + x ) - x;
	}
	if ( ax < FLOAT_EPS ) {
		return -x * x / 2.0;
	}
	opts = {
		'initialValue': -x
	};
	return sumSeries( log1pSeries( x ), opts );
}
Evaluates \\( \operatorname{log1pmx}(x) = \ln(1+x) - x \\).

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

@example
var v = log1pmx( 1.1 );
// returns ~-0.358

@example
var v = log1pmx( 0.99 );
// returns ~-0.302

@example
var v = log1pmx( -0.99 );
// returns ~-3.615

@example
var v = log1pmx( -1.1 );
// returns NaN

@example
var v = log1pmx( NaN );
// returns NaN