presto-main/src/main/java/io/prestosql/operator/aggregation/DecimalAverageAggregation.java/DecimalAverageAggregation/accumulateAndUpdateOverflow
class DecimalAverageAggregation:    private static void accumulateAndUpdateOverflow(Slice unscaledValue, LongDecimalWithOverflowAndLongState state)
    {
        initializeIfNeeded(state);
        Slice sum = state.getLongDecimal();
        long overflow = UnscaledDecimal128Arithmetic.addWithOverflow(sum, unscaledValue, sum);
        state.setOverflow(state.getOverflow() + overflow);
    }