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 ;)
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slightwv (䄆 Netminder) Commented:
I don't know RPG but from a quick google, looks like compare and branch:
David Johnson, CDRetiredCommented:
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                            

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;

Open in new window

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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aelessedilAuthor Commented:
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 ;)
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