presto-main/src/main/java/io/prestosql/type/DecimalOperators.java/DecimalOperators/divideRescaleFactor
class DecimalOperators:    private static List<Object> divideRescaleFactor(PolymorphicScalarFunctionBuilder.SpecializeContext context)
    {
        DecimalType returnType = (DecimalType) context.getReturnType();
        int dividendScale = toIntExact(requireNonNull(context.getLiteral("a_scale"), "a_scale is null"));
        int divisorScale = toIntExact(requireNonNull(context.getLiteral("b_scale"), "b_scale is null"));
        int resultScale = returnType.getScale();
        int rescaleFactor = resultScale - dividendScale + divisorScale;
        return ImmutableList.of(rescaleFactor);
    }