docs: static int computeCombinedBufferItemCapacity(final int k, final long n) {
      final int totLevels = computeNumLevelsNeeded(k, n);
      if (totLevels == 0) {
        final int bbItems = computeBaseBufferItems(k, n);
        return Math.max(2 * DoublesSketch.MIN_K, ceilingPowerOf2(bbItems));
      }
      return (2 + totLevels) * k;
    }