On Wed, 3 Sep 2025 10:52:27 +0000 Seymour J Metz <sme...@gmu.edu> wrote:
:>What are CLCL, MVCL and friends, chopped liver? R0 is perfectly valid and is used to address storage when specified, except when the associated length is zero. His point was AR0, which is not used by these instruction (the address in R0 is treated as in the primary address space) :>Shmuel (Seymour J.) Metz :>http://mason.gmu.edu/~smetz3 :>??? ?????????? ??? :>?????? ??????????? ???? ?????????? :> :> :> :> :>________________________________________ :>From: IBM Mainframe Assembler List <ASSEMBLER-LIST@LISTSERV.UGA.EDU> on behalf of Steve Smith <00001b5163999d8a-dmarc-requ...@listserv.uga.edu> :>Sent: Tuesday, September 2, 2025 10:27 PM :>To: ASSEMBLER-LIST@LISTSERV.UGA.EDU <ASSEMBLER-LIST@LISTSERV.UGA.EDU> :>Subject: Re: Using (0) to suppress alignment checks in HLASM :> :> :>External Message: Use Caution :> :> :>Well, I dispute that. In most instructions, 0 in an R field has nothing to :>do with register 0. It explicitly means *no* register is used, and the :>value of 0 is. It's just solipsistic to say the machine "considers" :>register 0 to be 0. The language in the PoOp is more like you cannot use :>register 0 for addressing in most cases. :> :>And as far as I can tell, you can't use access register 0 for anything :>other than volatile temporary storage. :> :>sas :> :> :>On Tue, Sep 2, 2025 at 1:37?PM Tony Harminc <t...@harminc.com> wrote: :> :>> On Tue, 2 Sept 2025 at 13:05, Steve Smith < :>> 00001b5163999d8a-dmarc-requ...@listserv.uga.edu> wrote: :>> :>> Is there such a thing as an implicit index register? ;-) :>> > :>> :>> Yes, there is. All RX instructions have an index register - it's not in any :>> sense optional at the machine code level - if you don't explicitly provide :>> one in the assembler language then the assembler will generate the :>> instruction using 0. (And of course register 0 when used as an index is :>> deemed to have the value 0.) It's extremely common for RX instructions to :>> be used in contexts where no index register is needed. :>> :>> But I'm sure you know all this. Now if you had asked "is there such a thing :>> as specifying an implicit index register?", then that would have a :>> different answer. ;-) :>> :>> Tony H. :>> :> :> -- Binyamin Dissen <bdis...@dissensoftware.com> http://www.dissensoftware.com Director, Dissen Software, Bar & Grill - Israel
