Currency calculation wrong

General
1

Just reported via Feedback: <https://xojo.com/issue/53197>

If we do math like this:

dim c as currency = 161.64 dim e as Currency = c * 100 dim d as int64 = c * 100 Break

e is 16164 which is correct, but d is 16163, which is not correct.

Can we make sure that math like this correct?

e.g. internally I would expect that c is 1616400 and multiply by 100 is actually a divide by 100 with conversion to Int64.

2

Did this test:

Dim c As Currency = 161.64 Dim e As Currency = c * 100 Dim d As Int64 = c * 100 Dim f As Double = c Dim g As Double = c * 100 Dim h As Double = 161.64 Dim i As Int64 = e Break

Of course I don’t know what is going on internally, but it looks like:

Dim d As Int64 = c * 100

first c is changed to the double value (161.639…) then * 100, so the result d is 16163 and i is correct with 16164

3

Well, it would be good if the compiler could be a bit more clever here.
e.g. use round for double -> int64.

Even better would be if compiler sees that currency is an int64 internally, so it can change *100 to /100 in this conversion.

4

I agree Christian, I expect this:
See ‘c’ as currency, check that there is an operation, treat the operation as currency, then the final result (as currency) assign it to ‘d’ that is Int64.

Something like:

Dim c As Currency = 161.64 Dim e As Currency = c * 100 Dim d As Int64 = c * 100 // currency, same as 'e'

I guess the currency calculation is not wrong, but the way the calculation is done when assigned to a non currency variable, right?

6

This works though…

Dim e As Int64 = ctype(c * 100, currency)

and so does:

Dim d as Int64 = e

That probably means that you should do all of your currency calculations using Currency typed variables and then convert to something else.

7

The problem is that we want to trust in the data types and know you guys have tons of test cases to make sure they work well in all ways.

8

I think this is the first time I see ‘ctype’ (still lot to learn). Reading about ctype I see this:

Then what Greg posted:

Dim e As Int64 = ctype(c * 100, currency)

Then what an user could expect with c is currency but we are using = to Int64:
a) c considered as Int64 then * 100, result should be 16100, like:

Dim c As Currency = 161.64 Dim d As Int64 = c d = d * 100
or
b) c considered as currency * 100, result converted to Int64, like:

Dim c As Currency = 161.64 Dim e As Currency = c * 100 Dim d As Int64 = e

but in reality we get d = 16163

Dim c As Currency = 161.64 Dim d As Int64 = c * 100

If we use a decimal plugin with this code:

Dim c As Decimal = 161.64 Dim d As Int64 = c * 100
we get d = 16164
as we original expected. My guess is, because the decimal plugin is not a Xojo data type, then Xojo does not convert it to double to do the * 100 calculation and we get the expected result.

9

After doing some tests and re-reading the ctype notes, I think the problem is with the “implicit conversion”.

Original code:

Dim c As Currency = 161.64 Dim e As Int64 = c * 100

Expected result (using code):

Dim c As Currency = 161.64 Dim e As Int64 = ctype(c * 100, Currency)

Actual result (equal to):

Dim c As Currency = 161.64 Dim e As Int64 = ctype(c * 100, Double)

I expected the implicit conversion to “see” that c is currency and do a currency calculation and not as double.

Edit: I see <https://xojo.com/issue/53197> marked as Verified