Yes, only clear low 32-bits of 64-bit registers. I've seen method #3 in IBM code or documentation, which makes one wonder why they used it instead of SR.
I forgot about LA Rn,0. -----Original Message----- From: IBM Mainframe Assembler List <ASSEMBLER-LIST@LISTSERV.UGA.EDU> On Behalf Of Mike Hochee Sent: Monday, August 10, 2020 2:50 PM To: ASSEMBLER-LIST@LISTSERV.UGA.EDU Subject: Re: Clearing a register I tend to use XR or XGR and LLIHF or LLILF. SRA does not operate against all 32 bits, and sometimes I do not want to think about extras like sign extension with LHI. (I know, it's not much to have to think about) I suppose if you want compatibility with machines of 30/40 years ago you might tend towards XR and SR. My 2 cents worth, Mike -----Original Message----- From: IBM Mainframe Assembler List [mailto:ASSEMBLER-LIST@LISTSERV.UGA.EDU] On Behalf Of Schmitt, Michael Sent: Monday, August 10, 2020 3:13 PM To: ASSEMBLER-LIST@LISTSERV.UGA.EDU Subject: Clearing a register Caution! This message was sent from outside your organization. There are many ways to set a register to binary zero. My question is, which is the most efficient? 1. XR Rn,Rn 2. SR Rn,RN 3. SRA Rn,Rn 4. LHI Rn,0 5. Other instruction 6. Depends on hardware 7. Depends on other factors. (What?) 8. They all have equal performance 9. Method X has worse performance but other advantages. (What?) ____________________________________ Michael Schmitt | DXC.technology (469) 808-4403 | michael.schm...@dxc.com DXC Technology Company - Headquarters: 1775 Tysons Boulevard, Tysons, Virginia 22102, USA. DXC Technology Company -- This message is transmitted to you by or on behalf of DXC Technology Company or one of its affiliates. It is intended exclusively for the addressee. The substance of this message, along with any attachments, may contain proprietary, confidential or privileged information or information that is otherwise legally exempt from disclosure. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient of this message, you are not authorized to read, print, retain, copy or disseminate any part of this message. If you have received this message in error, please destroy and delete all copies and notify the sender by return e-mail. Regardless of content, this e-mail shall not operate to bind DXC Technology Company or any of its affiliates to any order or other contract unless pursuant to explicit written agreement or government initiative expressly permitting the use of e-mail for such purpose. --.
