RE: How can I Improve this procedure... -- RPG400-L

Not really.
With a parameter, a temporary/work variable is created, but data is copied into
it once. Nothing is returned, so there isn't that subsequent copying going on
upon return.
Passing by VALUE also prohibits access to the changed data of the parameter.
This is a different situation than the return value of a subprocedure.



-Bob Cozzi
www.RPGxTools.com
RPG xTools - Enjoy programming again.

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On
Behalf Of praveen gunda
Sent: Wednesday, April 19, 2006 3:40 PM
To: RPG programming on the AS400 / iSeries
Subject: Re: How can I Improve this procedure...

Is this the same with the parameters passed to a procedure by Value.

Eg: myProc('hello')

D myProc        PI
D     parm1                    10 a Value


In the above example, is 'Hello' copied twice?
1. once from 'hello' --> 1024A work field
2. from 1024A (work field) --> parm1

Thanks
Praveen


On 4/19/06, Bob Cozzi <cozzi@xxxxxxxxx> wrote:
>
> A return value that is not an Integer or a Pointer is specified on the
> RETURN
> opcode.
> The system copies that to a work field that is the size and shape of the
> definition of the return value itself. So if you return a 10a field to a
> return
> value that is 1024a that 10A value is copied to a work field that is
> 1024A.
> Then that 1024a workfield is copied to the expression in which is it used.
> This
> is a second copy for which you have no control over.
> So now you've got data being copied twice, at minimum.
> If you do something like
>
> mycharVar = myProc('hello')
>
> and myProc returns that 1024a value, it now has to copy the second
> work/temp
> variable's value to the mycharVar field. So that's 3 copies.
>
> Why are long return parameters slow? Because they are copied (typically)
> at
> least 3 times and no fewer than twice.
>
> -Bob Cozzi
> www.RPGxTools.com
> RPG xTools - Enjoy programming again.
>
>
> -----Original Message-----
> From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
> On
> Behalf Of praveen gunda
> Sent: Wednesday, April 19, 2006 2:38 PM
> To: RPG programming on the AS400 / iSeries
> Subject: Re: How can I Improve this procedure...
>
> Scott,
> "However, if the problem is that you don't believe me, you can wait until
> an IBMer on the list replies."
>
> I always like the explanations you give. It thows a lot of light on the
> subject. You give excellent replies.
> That is one reason I dare to ask questions in this forum. I get excellent
> replies from very experianced people here.
>
> One reason I asked for references is, so that I can convince others if
> they
> question me.
>
>
>
>
>
> On 4/19/06, Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx> wrote:
> >
> >
> > > can you elaborate on this? I keep hearing it very often but did not
> find
> > > much explantation as to why?
> >
> > Because a return value copies the data from one place to another.  So if
> > you return 3000 bytes, the system has to copy all 3000 bytes from one
> > place in memory to another place in memory.
> >
> > By contrast, when you pass a parameter (unless you use the VALUE
> keyword)
> > the system references the existing copy of the data in memory. It
> doesn't
> > have to copy it from one place to another, it just uses the original
> spot.
> >
> > > Is this the case with procedures too? Also is it any different if the
> > > procedure is in a service program?
> >
> > Since programs can't return a value, this discussion ONLY applies to
> > procedures, and that's what we've been talking about all along. Unless
> I'm
> > misinterpreting the question?
> >
> > No, it doesn't matter if the procedure is in a service program. (or
> > anywhere else)  This has to do with how parameters and return values
> work.
> > It doesn't matter where the procedures are located.
> >
> > > Is it not just a pointer that is returned? Any pointers to books/IBM
> > > resources on this topic will be helpful too.
> >
> > No, it is not a pointer that's returned.   I'm sure that there are IBM
> > resources that explain this, but I don't know what they are off the top
> of
> > my head.  I learned this stuff years and years and years ago, and I'm
> > afraid that I can no longer remember where I originally learned it.
> >
> > However, if the problem is that you don't believe me, you can wait until
> > an IBMer on the list replies.
> >
> > >>       D                 DS
> > >>       D ReasonDS                            dim(200)
> > >>       D  @RsnCode                      2A   overlay(ReasonDS:1)
> > >>       D  @Charge                       9P 2 overlay(ReasonDS:*NEXT)
> > >>       D  @Weight                       9P 0 overlay(ReasonDS:*NEXT)
> > >>       D  @Units                        7P 0 overlay(ReasonDS:*NEXT)
> > [SNIP]
> > >
> > > In this case does RPG allow  %lookup('XX': @RsnCode)  ?  I guess not
> as
> > > @RsnCode is not an array.
> >
> > Sorry, @RsnCode *is* an array, and yes you can use %lookup() on it.
> > That's the reason I suggested this technique.   The reason that it's an
> > array is because it's overlaying ReasonDS which is an array.
> >
> > [SNIP]
> > >>       D ReasonDS        ds                  qualified dim(200)
> > >>       D  @RsnCode                      2A
> > >>       D  @Charge                       9P 2
> > >>       D  @Weight                       9P 0
> > >>       D  @Units                        7P 0
> > [SNIP]
> > > This is exactly what I meant to do, but for the lack of %lookup
> support.
> > > Would it be possible to write a generic procedure, you can pass an
> array
> > > (could be an array of datastructure) that could look up this array...
> I
> > am
> > > just thinking loud here.
> >
> > You could write a subprocedure that loops through it and compares the
> > elements.  That way, you can call that subprocedure to do a lookup.
> >
> > Alternately, you could use the qsort() and bsearch() routines from the
> ILE
> > C runtime.  This has been discussed many times before, so searching the
> > archives should yield some examples.
> >
> > Of course, the overlay approach allows you to use %LOOKUP so you might
> not
> > even want to use the qualified DIM DS approach.  I'm just telling you
> what
> > your options are.
> >
> > --
> > This is the RPG programming on the AS400 / iSeries (RPG400-L) mailing
> list
> > To post a message email: RPG400-L@xxxxxxxxxxxx
> > To subscribe, unsubscribe, or change list options,
> > visit: http://lists.midrange.com/mailman/listinfo/rpg400-l
> > or email: RPG400-L-request@xxxxxxxxxxxx
> > Before posting, please take a moment to review the archives
> > at http://archive.midrange.com/rpg400-l.
> >
> >
> --
> This is the RPG programming on the AS400 / iSeries (RPG400-L) mailing list
> To post a message email: RPG400-L@xxxxxxxxxxxx
> To subscribe, unsubscribe, or change list options,
> visit: http://lists.midrange.com/mailman/listinfo/rpg400-l
> or email: RPG400-L-request@xxxxxxxxxxxx
> Before posting, please take a moment to review the archives
> at http://archive.midrange.com/rpg400-l.
>
>
> --
> This is the RPG programming on the AS400 / iSeries (RPG400-L) mailing list
> To post a message email: RPG400-L@xxxxxxxxxxxx
> To subscribe, unsubscribe, or change list options,
> visit: http://lists.midrange.com/mailman/listinfo/rpg400-l
> or email: RPG400-L-request@xxxxxxxxxxxx
> Before posting, please take a moment to review the archives
> at http://archive.midrange.com/rpg400-l.
>
>