prePEP: Money data type

[Alex Martelli]

Paul Rubin wrote:

> "John Roth" <newsgroups at jhrothjr.com> writes:
>> COBOL's default rounding policy is to truncate. It has a second
>> rounding policy that is invoked by the keyword ROUND (surprise,
>> eh?) However, one of the things that COBOL arithmetic has is
>> precise control of the number of decimal places at all points in
>> a computation[1], so if you don't like either truncation or the effects
>> of ROUND, then you simply maintain an additional decimal place
>> or two and do it your way.[2]
> 
> Yeah, but what about the exact method of rounding, like the pre-PEP
> specifies 1.125 rounds down but 1.135 rounds up (or maybe it was the
> other way), while some other standard specifies always rounding down
> (or up) when the extra digit is a 5.

Round-to-even-cent is quite popular (Roguewave calls it "Banker's
Rounding" in the Money class of their commercial class library).
So is always-round-up (again in the case in which an exact
computation would end up with a half cent, or whatever other
least significant unit of measure), which Roguewave calls "Plain
Rounding", and the European Union specifies.

If you have a type that only performs one kind of rounding, you
cannot use that type for legally valid money computations in
both Europe AND America (I think: I haven't been shown American
laws specifying rounding approaches, have just seen that "round
to even" mentioned as being usual, habitual, or popular).


Alex