Re: Date compare Best Practices -- RPG400-L

On Friday, February 27, 2004, at 07:21 AM, Bob Cozzi wrote:

There is nothing wrong with using the "MULT 10000.01" technique in RPGIII. I do it every time I need to convert a date in that old language.

It was always a dumb idea--even in RPG III. It causes an arithmetic exception every time it is used. Exceptions hurt performance.

It is obscure because it relies on arithmetic truncation present in RPG but not present in other languages (and also not present in EVAL).

It is obscure because it is not immediately obvious from the code what is happening. The first time anyone sees the MULT trick they either ask someone and accept the answer "It converts the date format" or they work it out on paper to see what happens. Either approach indicates the technique is not obvious. The result is programmers who perpetuate a bad habit because they don't understand what it is doing. They are just familiar with it. A case of "That's how we've always done it".

If you use it in RPG IV, then you are right it is a questionable choice. The only other technique in RPG III is to use a data structure, but that can be a bit more complex that the MULT. If you haven't seen it before then it doesn't matter which one you use because the person maintaining the code after you will have to deal with it, so just be sure to document it properly.

Data structure moves are much more obvious, especially if decent variable names are used. Three obvious MOVE statements are not more complex than one obscure MULT operation. The moves are also much faster. Test both techniques some time and see for yourself.

While doing a few conversions per host interaction may not cause a noticeable performance impact using the same trick on a large database file with many dates will. Much better to be consistent and use the faster AND more obvious approach everywhere.

The MULT trick falls in the category of clever (read stupid) programming tricks and should be avoided--especially by people who teach others.

Regards,
Simon Coulter.
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