RE: Z-ADD or Eval?

["jt" <jt@xxxxxx>]

Jim

I was always told that, on the S/38, MOVE and Z-ADD created the exact same
MI instruction.  I verified this is still true today by looking at the IRP
from an RPG compile by specifying GENOPT(*LIST).  Both use the same MI
instruction 'copy numeric value 0.0 to field X':

CPYNV X,P'0.0'

It is unlikely that ILE RPG would be any different, but since you cannot get
the IRP list for ILE programs, it's hard to say for sure.

(BTW, I also use *ZEROS, just for readability.)

jt

-----Original Message-----
From: owner-rpg400-l@midrange.com [mailto:owner-rpg400-l@midrange.com]On
Behalf Of Jim Langston
Sent: Tuesday, August 22, 2000 5:15 PM
To: RPG400-L@midrange.com
Subject: Re: Z-ADD or Eval?


Z-Add being faster than Move all has to do with the assembly language
instruction.  Z-Add actually maps to a specific assembly langauge
instruction,
which was called ZADD, I believe, in the 80x86 series of chips, probably the
same in the IBM chip (Motorolla?)

I don't know what happened to the Z-Add instruction on the new RISC chips,
or even if it's faster anymore. But we are talking like 2 or 3 chip cycles
anyway.

The reason I'm not using %Found and such is because I'm on V3R7M0 and
it doesn't seem to have them.

Okay, I'll go with the Eval.

Incedently, who do you use 0 instead of *Zero?  *Zero is just easier for me
to read.

Regards,

Jim Langston

Scott Klement wrote:

> Ummm...  why would Z-Add be more efficient than MOVE? That seems odd to
> me.  Math is slower than just moving bytes around...
>
> Your code doesn't look modern to me because it uses an indicator :)
> You should find a way to do this that doesn't involve an indicator.
>
> If you're only doing a single line of code (as in your examples) I find
> conditioning indicators to be just as good as if statements.  But, if
> you're going to do more than one line of code conditioned on that same
> indicator, the "if" technique is better.
>
> This is how I code things like that, when I _must_ use indicators:
>
> c   99              eval       EqSize = 0
>
> or:
>
> c                   if         *in99
> c                   eval       EqSize = 0
> c                   endif
>
> I doubt I'll ever use Z-ADD again.  :)
>

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