question: private static void sparseProbabilisticOverlapTest ( final ISchemaVersion schemaVersion ) throws IOException { final Writer output = openOutput ( schemaVersion , "sparse_sparse" , TestType . UNION ) ; final Random random = new Random ( randomLong ( ) ) ; final HLL hll = newHLL ( HLLType . EMPTY ) ; final HLL emptyHLL = newHLL ( HLLType . EMPTY ) ; cumulativeUnionLine ( output , hll , emptyHLL , schemaVersion ) ; for ( int i = 0 ; i < SPARSE_THRESHOLD ; i ++ ) { final HLL sparseHLL = newHLL ( HLLType . SPARSE ) ; final int registerIndex = Math . abs ( random . nextInt ( ) ) % REGISTER_COUNT ; final int registerValue = ( ( Math . abs ( random . nextInt ( ) ) % REGISTER_MAX_VALUE ) + 1 ) ; final long rawValue = constructHLLValue ( LOG2M , registerIndex , registerValue ) ; sparseHLL . addRaw ( rawValue ) ; cumulativeUnionLine ( output , hll , sparseHLL , schemaVersion ) ; } output . flush ( ) ; output . close ( ) ; }
target:  Unions an EMPTY accumulator with SPARSE HLLs, each having a single register set, twice in a row to verify that the set properties are satisfied. Format: cumulative union Tests: - EMPTY U SPARSE - SPARSE U SPARSE