Path: ...!news.iecc.com!.POSTED.news.iecc.com!not-for-mail
From: John Levine <johnl@taugh.com>
Newsgroups: comp.arch
Subject: Re: mainframe Byte Addressability And Beyond
Date: Fri, 31 May 2024 19:41:01 -0000 (UTC)
Organization: Taughannock Networks
Message-ID: <v3d94d$s9a$1@gal.iecc.com>
References: <v0s17o$2okf4$2@dont-email.me> <v39caf$1jtgk$1@dont-email.me> <v3a386$14g8$1@gal.iecc.com> <v3cg8v$27oob$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Injection-Date: Fri, 31 May 2024 19:41:01 -0000 (UTC)
Injection-Info: gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970";
	logging-data="28970"; mail-complaints-to="abuse@iecc.com"
In-Reply-To: <v0s17o$2okf4$2@dont-email.me> <v39caf$1jtgk$1@dont-email.me> <v3a386$14g8$1@gal.iecc.com> <v3cg8v$27oob$1@dont-email.me>
Cleverness: some
X-Newsreader: trn 4.0-test77 (Sep 1, 2010)
Originator: johnl@iecc.com (John Levine)
Bytes: 2211
Lines: 27

According to Terje Mathisen  <terje.mathisen@tmsw.no>:
>> Read all about it: https://www.vm.ibm.com/library/other/22783213.pdf
>> 
>> It's on page 7-251.
>> 
>Thanks!
>
>I did read all of it, and it was pretty close to how I would have 
>designed a sw function to do the same, except for the very funky ABI:
>
>Both source and destination _must_ be an even register number, with the 
>following odd register providing the count/length.

That's the way they've been handling address+length pairs since they
added long compare and move instructions in S/370.  They're so common
I'd expect there to be hardware to deal with them.

>Just from this little snippet I'm pretty sure this instruction has a 
>sizeable startup overhead, compiler support is probably in the form of 
>an intrinsic that knows about the need to allocate two pairs of 
>register, each pair starting at an even-numbered register.

Same register allocation would be needed for a string compare or move,
so that's nothing new.
-- 
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly