Oppolzer - Informatik / Blog

I recall that I had some difficulties with the PoOp when I first had to use it
in the mid 1980s, maybe with this numbering scheme of the operands, but must
operations involve only two operands, some have three, and it is always clear
from the context, what happens. BTW: we had a PoOp translated to German in those
days which was not bad - normally I don't like translated IBM brochures, because
they have bugs - the English originals are better IMHO.

But, when you once get accustomed to the logic of the PoOp, it's no problem any
more.

Kind regards

Bernd



Am 20.02.2013 06:23, schrieb J.E.:
> P.G. noted:
>> I would be careful not to create confusion by inviting undue attention
>> to the notion of "sequential position".
>      COMPARE AND SWAP
>      CS    R1,R3,D2(B2)    [RS-a]
>
> If you wrote
>      CS      0,4,X
> the assembler says operand 1 is 0, operand 2 is 4, and operand 3 is X,
> while the PoP swaps the latter two.
>
> Assembler programmers must deal with the confusion caused by multiple uses
> of the word "operand". The PoP sense (and numbering) is different from the
> assembler's sense. Sadly, the assembler's notation is just as old as that
> of the PoP, and generations of assembler programmers have had to cope with
> the differences..