function aversin( x ) {
	return acos( 1.0 - x );
}
Computes the inverse versed sine.

@param {number} x - input value
@returns {number} inverse versed sine

@example
var v = aversin( 0.0 );
// returns 0.0

@example
var v = aversin( 3.141592653589793/2.0 );
// returns ~2.1783

@example
var v = aversin( 3.141592653589793/6.0 );
// returns ~1.0742

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