On Tue, 18 Mar 2025 10:28:23 -0400 Phil Smith III <[email protected]> wrote:
:>This isn't the length, it's the address (target). :> :>I've been puzzling at this for a bit. Am I correct in concluding that OP's point is: :>1) In non-AR mode, a target register of 0 means "move to location 0" (assuming non-zero input length), in the home address space, of course In all RR(E) instructions the contents of R0 are used, even when addressing data. My point was that in the RR instructions 0 is never a placeholder for nothing - it is an explicit register. BTW, primary, not home. And not location zero. :>2) In AR mode, it means the same, EVEN IF AR0 is set In AR mode, AR0 is not used to address data. :>3) OP is suggesting that it would make more sense if AR0 were honored in this case I could see both ways. :>? If so, then I can see OP's point. MVCLing to location 0 in the home address space is pretty unlikely; less so in AR mode. But...this is how it's implemented and documented, so not likely to change. And of course there are other registers that can be used to move to location 0 in AR mode, so it's not like it makes something impossible. Move to location zero in the primary address space (ZOS) will get a pic-4 low address protection unless the CR's are fiddled with. :>-----Original Message----- :>From: IBM Mainframe Discussion List <[email protected]> On Behalf Of Robin Vowels :>Sent: Tuesday, March 18, 2025 10:13 AM :>To: [email protected] :>Subject: Re: AR Mode: MVCL R0,Rx No; MVCL Rx,Ry Yes :> :>Enlighten me. :>What is the purpose of AR mode? :> :>Does not a length of zero mean that the content of the corresponding address register not be used? -- Binyamin Dissen <[email protected]> http://www.dissensoftware.com Director, Dissen Software, Bar & Grill - Israel ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
