code: func checkBlockSize(blockSize, minBlockSize, maxBlockSize int) int {
  	assert2(blockSize >= minBlockSize && blockSize <= maxBlockSize,
  		"blockSize must be >= %v and <= %v, got %v",
  		minBlockSize, maxBlockSize, blockSize)
  	assert2((blockSize&(blockSize-1)) == 0,
  		"blockSIze must be a power of 2, got %v", blockSize)
  	return TrailingZeros[blockSize]
  }
docs: /* Check that the block size is a power of 2, in the right bounds, and return its log in base 2. */