code: protected float getSizeArcLength(float angle) {
          if (mRadius <= 0) {
              throw new IllegalArgumentException("mRadius is not specified!");
          }
          return angle == Float.MAX_VALUE ? Float.MAX_VALUE :
                  LayoutHelpers.lengthOfArc(angle, mRadius);
      }
docs: Calculate the arc length by angle and radius
  @param angle
  @return arc length