presto-main/src/main/java/io/prestosql/type/DecimalOperators.java/DecimalOperators/internalAddLongLongLong
class DecimalOperators:    private static Slice internalAddLongLongLong(Slice a, Slice b, int rescale, boolean rescaleLeft)
    {
        try {
            Slice left = unscaledDecimal();
            Slice right;

            if (rescaleLeft) {
                rescale(a, rescale, left);
                right = b;
            }
            else {
                rescale(b, rescale, left);
                right = a;
            }

            UnscaledDecimal128Arithmetic.add(left, right, left);
            throwIfOverflows(left);
            return left;
        }
        catch (ArithmeticException e) {
            throw new PrestoException(NUMERIC_VALUE_OUT_OF_RANGE, "Decimal overflow", e);
        }
    }