code: private static int compressionLevel(int blockSize) {
  		int compressionLevel = 32 - Integer.numberOfLeadingZeros(blockSize - 1); // ceil of log2
  		assert (1 << compressionLevel) >= blockSize;
  		assert blockSize * 2 > (1 << compressionLevel);
  		compressionLevel = Math.max(0, compressionLevel - COMPRESSION_LEVEL_BASE);
  		assert compressionLevel >= 0 && compressionLevel <= 0x0F;
  		return compressionLevel;
  	}
docs: endregion