>> "is there such a thing as specifying an implicit index register?",
I don't know about anybody else but, to me, "specify" and "imply" are opposites unless you're actually talking about "overriding" a default "implicit" value (meaning, specifying your own implicit/default value). Then the answer is, "No." Sincerely, Dave Clark -- int.ext: 91078 direct: (937) 531-6378 home: (937) 751-3300 Winsupply Group Services 3110 Kettering Boulevard Dayton, Ohio 45439 USA (937) 294-5331 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. > > > > On Tue, Sep 2, 2025 at 7:11 AM Jonathan Scott < > > 00001b5498fc732f-dmarc-requ...@listserv.uga.edu> wrote: > > > > > This technique relies on the rule that including an explicit index > > > register in an address expression suppresses the alignment warning, > even > > if > > > that index register is zero (which may originally have been an > > oversight). > > > HLASM's own source code uses this technique, so it should be safe to > use. > > > I thought I had submitted a documentation update request a few years > ago > > to > > > ensure this was properly documented, probably as part of the > explanation > > of > > > message ASMA033I (which already shows how to use an explicit base > > > register), but I can't find any mention in the current documentation, > and > > > having retired from IBM I no longer have access to the request queue > so I > > > can't tell whether it is still in the queue. > > > > > > Jonathan Scott > > > > > > -----Original Message----- > > > From: IBM Mainframe Assembler List <ASSEMBLER-LIST@LISTSERV.UGA.EDU> > On > > > Behalf Of Peter Morrison > > > Sent: 02 September 2025 11:10 > > > To: ASSEMBLER-LIST@LISTSERV.UGA.EDU > > > Subject: Using (0) to suppress alignment checks in HLASM > > > Importance: High > > > > > > Hello, > > > > > > Has anyone else used (0) at the end of an RX (or RXY) > > > instruction to suppress the assembler's alignment check? > > > > > > For Example: > > > > > > DC X'00' force next field to be > > > unaligned > > > X_UNAL DC AL4(0) Declare an unaligned fullword > > > > > > L R0,X_UNAL > > > gets a warning > > > L R0,X_UNAL(0) > > > same generated code (ix reg is 0) but no warning > > > > > > If so, where is it documented? (this is easier than a > > > <PUSH ACONTROL/ACONTROL NOALIGN/instr/POP ACONTROL> sequence (and takes > > no > > > extra lines)) > > > > > > Peter Morrison > > > > > >
