private int calculateSumForBlock(int blockIndex, int lastLongIndex) {
    int sum = 0;
    if (blockIndex > 0) sum = mySubSumOfBlocks[blockIndex - 1];

    for (int longIndex = blockIndex * myBlockSize; longIndex <= lastLongIndex; longIndex++) {
      if (myVisibility.get(longIndex)) sum++;
    }
    return sum;
  }
private int calculateSumForBlock(int blockIndex, int lastLongIndex)