Re: [Re: RPGILE V4.3 Gotcha]

[boldt@xxxxxxxxxx]

Jim wrote:
>Okay, let me just say it this way then, it is not safe to do ANY type
>of math on any number that contains a fraction.
>
>If I have to worry about loosing accuracy after ONE significant digit,
>something is definitely wrong with the math engine.


Jim:  Have you studied Chapter 21 of the ILE RPG Reference
manual?

You want decimal arithmetic to be done precisely regardless
of the size of the value?  Here's how to do it:  Do your
arithmetic in a REXX program with the following statement:

       NUMERIC DIGITS 1000

(If a thousand digits isn't good enough, just change it to a
bigger number.)  But guess what the performance of your
program will be like?

Although the performance of interpreted languages is becoming
a less significant factor in choice of programming language,
most shops tend to prefer the performance advantages of
compiled languages.  But these performance advantages come
with constraints, such as RPG's 30 digit maximum on the
precision of decimal values.  (Or IEEE's design of floating
point values, which limits precision to no more than 17
digits, at best.)

I take issue with your assertion that it is not safe to do
ANY type of math on any number that contains a fraction.
(I'm sure the vast majority of programmers who do code their
arithmetic in expressions would also disagree!)  The rules
for decimal arithmetic in expressions are documented in
Chapter 21 of the ILE RPG Reference.  If you want to be able
to code decimal expresssions safely, you need to understand
those rules.  If you still have questions after studying
Chapter 21, I'd be quite happy to answer them.

You could always stick to the traditional ADD, SUB, MULT, etc
opcodes.  But since the default behavior of those is to
truncate results instead of failing on numeric overflow,
those opcodes are the real unsafe ones!

Cheers!  Hans

Hans Boldt, ILE RPG Development, IBM Toronto Lab, boldt@ca.ibm.com


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