presto-parquet/src/main/java/io/prestosql/parquet/dictionary/DictionaryReader.java/DictionaryReader/initFromPage
class DictionaryReader:    @Override
    public void initFromPage(int valueCount, ByteBufferInputStream in)
            throws IOException
    {
        int bitWidth = BytesUtils.readIntLittleEndianOnOneByte(in);
        decoder = new RunLengthBitPackingHybridDecoder(bitWidth, in);
    }