Re: Date compare Best Practices

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

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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