presto-orc/src/main/java/io/prestosql/orc/reader/LongColumnReader.java/LongColumnReader/readBlock
class LongColumnReader:    @Override
    public Block readBlock()
            throws IOException
    {
        if (!rowGroupOpen) {
            openRowGroup();
        }

        if (readOffset > 0) {
            if (presentStream != null) {
                // skip ahead the present bit reader, but count the set bits
                // and use this as the skip size for the data reader
                readOffset = presentStream.countBitsSet(readOffset);
            }
            if (readOffset > 0) {
                if (dataStream == null) {
                    throw new OrcCorruptionException(column.getOrcDataSourceId(), "Value is not null but data stream is missing");
                }
                dataStream.skip(readOffset);
            }
        }

        Block block;
        if (dataStream == null) {
            if (presentStream == null) {
                throw new OrcCorruptionException(column.getOrcDataSourceId(), "Value is null but present stream is missing");
            }
            presentStream.skip(nextBatchSize);
            block = RunLengthEncodedBlock.create(type, null, nextBatchSize);
        }
        else if (presentStream == null) {
            block = readNonNullBlock();
        }
        else {
            boolean[] isNull = new boolean[nextBatchSize];
            int nullCount = presentStream.getUnsetBits(nextBatchSize, isNull);
            if (nullCount == 0) {
                block = readNonNullBlock();
            }
            else if (nullCount != nextBatchSize) {
                block = readNullBlock(isNull, nextBatchSize - nullCount);
            }
            else {
                block = RunLengthEncodedBlock.create(type, null, nextBatchSize);
            }
        }

        readOffset = 0;
        nextBatchSize = 0;

        return block;
    }