What is this really doing???

I've inherited some 10+ year old code without benefit of the original programmer... can anyone explain the usefulness of this code segment, or at least reduce to something more sensible?

Display Module Source

C N31USERN CABNE *ALL' ' 3131--

Thanks in advance ;)

First, it uses the indicator (boolean) labelled 31 (or IN31). The indicator can either be set to *ON or set to *OFF. If set to *OFF, it may be referenced as "N31". The "conditioning indicator" at the left says that this statement will execute if indicator 31 is *OFF.

The op-code is CABNE -- Compare and Branch if Not-Equal. Because no branch target is present, the only actual result will be setting IN31 to *ON or *OFF. The compare is done against the variable USERN and a value of all blanks.

Finally, the three possible results of a compare are greater-than, less-than and equal. On the right, IN31 is specified twice, once for greater-than and once for less-than. The equal state causes no change.

Pseudo-code might be like:

if IN31 = *OFF;
   if USERN <> ' ';
      IN31 = *ON;
   end-if;
end-if;

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I'm not sure why, but I've seen the CABNE op-code three times in the past week in various forums. It's been practically obsolete for more than a couple decades. If you go back in time much more than that, it was a way to say a lot in a very compact way and had a few advantages.

As systems became more powerful, it was just another op-code that outlived it's usefulness.

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LVL 80

slightwv (䄆 Netminder) Commented: 2018-11-21

I don't know RPG but from a quick google, looks like compare and branch:
https://www.ibm.com/support/knowledgecenter/SSPSQF_9.0.0/com.ibm.etools.iseries.langref.doc/evferlsh266.htm

LVL 90

David Johnson, CD, MVPOwnerCommented: 2018-11-21

The code is probably 20-40 years old. RPG is very column sensitive.. The last time I worked in RPG II was in 1980.
C (we will be doing a compare
N31USERN Operand 1 variable
CABNE - compare and branch if not equal
*ALL' ' compared to this is a literal not a variable
3131-- Tag or variable

http://www.go4as400.com/rpgle-opcodes/as400.aspx?cid=205

LVL 27

tliottaCommented: 2018-11-21

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aelessedilAuthor Commented: 2018-11-21

Thanks everyone! It seems I purged all this knowledge during Y2K, and frankly never used left-side indicators in conjunction with a factor variable.

I've a long uphill battle to update these programs to /Free... without the /Free of course ;)

What is this really doing???

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