presto-parquet/src/main/java/io/prestosql/parquet/reader/LongDecimalColumnReader.java/LongDecimalColumnReader/readValue
class LongDecimalColumnReader:    @Override
    protected void readValue(BlockBuilder blockBuilder, Type type)
    {
        if (definitionLevel == columnDescriptor.getMaxDefinitionLevel()) {
            Binary value = valuesReader.readBytes();
            type.writeSlice(blockBuilder, Decimals.encodeUnscaledValue(new BigInteger(value.getBytes())));
        }
        else if (isValueNull()) {
            blockBuilder.appendNull();
        }
    }