function hacoversin( x ) {
	return (1.0 - sin( x )) / 2.0;
}
Computes the half-value coversed sine.

@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