function hacoversin( x ) {
	return addon( x );
}
Computes the half-value coversed sine.

@private
@param {number} x - input value (in radians)
@returns {number} half-value coversed sine

@example
var v = hacoversin( 0.0 );
// returns 0.5

@example
var v = hacoversin( 3.141592653589793 / 2.0 );
// returns 0.0

@example
var v = hacoversin( -3.141592653589793 / 6.0 );
// returns 0.75

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