Re: Numerics PACKED, ODD format -- Always recommended?

-----Original Message-----
From: Booth Martin <boothm@ibm.net>


>Bob Crothers wrote:
>>
>> Karen,
>>
>> Yes, it is best (from a performance point of view) to use odd
>> length packed numeric data in your files.
>
>
>Doesn't db/400 ignore the packed vs. zoned definitions now?  I thought
>all numeric fields were packed regardless of what one writes in the dds.
>About the odd vs even issue: if you need 8 characters, then you need 8
>at least so you can't go to 7.  My understanding always was that the
>cycles for 8 are the same price as the cycles for 9, so the 9th
>character is a freebie, excepting dasd.


1) I've never heard anything about the system "ignoring" packed vs.. zoned
before.  I'm not saying you're wrong, just that that's a new one on me.
They could conceivably do that, but why would they?

2) In RPG there is a performance advantage to using odd-length packed,
because the compiler uses packed for all calculations and therefore must
convert non-packed numbers in both directions, and because when putting a
value into an even-length packed number an extra step is required to clear
the high-order nibble.  I have heard people say that they can tell a
difference in Performance Tools on calculation-intensive programs if they
"do it wrong", but I've never encountered a demonstrable instance of it
affecting user-perceived performance.  Maybe the people still running S/38
Model 4's need to be concerned, though... <grin>

Note that I'm saying "RPG", the situation is not exactly the same in Cobol,
PL/I, Java, C, etc., nor is it the same when doing calculations in SQL or
OPNQRYF.  My understanding is that AT THE MI LEVEL, there's no intrinsic
advantage of one fixed-point representation over the other on the /400, all
differences are due to implementation details in the relevant compilers,
interpreters, run-times, or whatever.

Dave Shaw, General Nutrition, Greenville, SC (just down the road from BMW -
Bubba Makes Wheels :)
The opinions expressed may not be my employer's unless I'm sufficiently
persuasive...


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