function signbit( x ) {
	// Extract from the input value a higher order word (unsigned 32-bit integer) containing the exponent and sign:
	var high = getHighWord( x );

	// Shift off all bits which are not the sign bit and check if the sign bit is on:
	return ( high >>> 31 ) ? true : false; // eslint-disable-line no-unneeded-ternary
}
Returns a boolean indicating if the sign bit is on (true) or off (false).

@param {number} x - input value
@returns {boolean} boolean indicating if sign bit is on or off

@example
var bool = signbit( 4.0 );
// returns false

@example
var bool = signbit( -9.14e-307 );
// returns true

@example
var bool = signbit( 0.0 );
// returns false

@example
var bool = signbit( -0.0 );
// returns true