function acovercos( x ) {
	return addon( x );
}
Computes the inverse coversed cosine of a double-precision floating-point number.

@private
@param {number} x - input value
@returns {number} inverse coversed cosine

@example
var v = acovercos( 0.0 );
// returns ~-1.5708

@example
var v = acovercos( 3.141592653589793/2.0 );
// returns ~0.6075

@example
var v = acovercos( 3.141592653589793/6.0 );
// returns ~-0.4966

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