public static float acos(float fValue) {
        if (-1.0f < fValue) {
            if (fValue < 1.0f) {
                return (float) Math.acos(fValue);
            }
            return 0.0f;
        }
        return PI;
    }
Returns the arc cosine of a value.<br>
Special cases:
<ul><li>If fValue is smaller than -1, then the result is PI.
<li>If the argument is greater than 1, then the result is 0.</ul>

@param fValue The value to arc cosine.
@return The angle, in radians.
@see java.lang.Math#acos(double)
jme3-core/src/main/java/com/jme3/math/FastMath.java