Re: last day of month (was MIDRANGE-L Digest V2 #1546)

[Jim Langston <jlangston@xxxxxxxxxxxxxxxx>]

Coming from various languages, I have learned never to trust the
initialized value of any variable.  I understand that this shouldn't be a
problem on the AS/400, but are we guaranteed that all variables will
be initialized to 0 (or their respective *lowval's?)

I find depending on an initialized value makes code very difficult to
understand an maintain.  I would just as well take the 2 nanosecond "hit"
and do an Eval   Isodd = 01     just to make my code crystal clear.

Regards,

Jim Langston

bmorris@ca.ibm.com wrote:

> >Date: Thu, 14 Oct 1999 09:16:48 -0700
> >From: Jon Erickson <jerickson@800.com>
> >
> >Correct me if I'm wrong,
> > ...
> >
> >d                 DS
> >d Isodate                         d   Inz
> >d  Isoyyyy                       4  0 Overlay(Isodate)
> >d  Isomm                         2  0 Overlay(Isodate:6)
> >
> >c                   Eval      Isoyyyy = Pyear
> >c                   Eval      Isomm = Pmonth
> >Add 1 month via ADDDUR
> >c                   AddDur    1:*Months     Isodate
> >
> >Subtract 1 day via SUBDUR
> >c                   SubDur    1:*Days       Isodate
>
> Sure, that will work.  I was discussing Jon's code to solve the general case 
>of
> getting the last day of the month containing a given date.
>
> Jon's code can be made to run a bit more quickly using overlays (you can get 
>rid
> of the extract by just setting the days part to "01").  Maybe that's a good
> idea,
> maybe not - it seems to me that using overlays makes the code a bit more
> complex.
>
> If you start with numeric year and month as in your example, your way is as 
>good
> as any.
>
> Hmm, I just thought of a way to use numeric year and month input avoiding
> overlays, with a single adddur:
>
> D date            s               d       datfmt(*iso) inz(D'0001-01-31')
>  * Find the number of months after 0001-01 for the given year and month
>  * E.g. for 0002-03, there are 12 + 1 months
> C                   eval      Pmonth = ((Pyear - 1) * 12) + (Pmonth - 1)
>  * Add them to Jan 31, 0001.  Month-end adjustment will fix up any results
>  * where the number of days in the month is less than 31.
> C                   adddur    Pmonth:*m     date
>
> With date operations, the contest should be regarding the number of date
> opcodes,
> not the number of statements.  (Date opcodes are very expensive.)
>
> Barbara Morris
>
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