MVCRL

[Schmitt, Michael]

Why isn't there a Move Relative Long instruction, i.e. move with no registers, where both the source and destination are relative to the instruction address?

Is this because there's no instruction format with two RI fields and a length?

[Ngan, Robert (DXC Luxoft)]

If the source is relative to the instruction address, the code would most like be non-reentrant.

Robert Ngan
DXC Luxoft

[Farley, Peter x23353]

Not if the code is executing in a getmained area. I've often put code in such areas for various reasons (e.g. OPEN exits, I/O error exits. etc.), and it's annoying to have to set up base registers.

But I confess I think an "MVCRL" instruction where *both* source and destination are relative to the instruction address would see little use. If only the SOURCE address was relative to the instruction address, that might be a tad more useful. Then the D(L,B) for the destination could be in a reentrant area.

Peter

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[Robin Vowels]

How would the instrction be interruptable?
How would the lengths of the source and destinations be specified?

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[Seymour J Metz]

Perhaps because IBM deemed it useless, or perhaps because instructions are limited to 48 bits.


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Shmuel (Seymour J.) Metz
http://mason.gmu.edu/~smetz3

________________________________________
From: IBM Mainframe Assembler List [ASSEMBL...@LISTSERV.UGA.EDU] on behalf of Schmitt, Michael [michael...@DXC.COM]
Sent: Tuesday, June 7, 2022 6:28 PM
To: ASSEMBL...@LISTSERV.UGA.EDU
Subject: MVCRL

[Martin Trübner]

Michael,


how is this

    MACRO

    MVCRL  &REC,&SEND,&LEN

    LARG     1,&REC

    LARG     15,&SEND

    MVC       0(&LEN,1),0(15)

   MEND

Destroys R1 and R15

Sender and receiver must be on HW boundry

Supports a max length of 256

Needs 18 bytes

Martin


Am 08.06.22 um 00:28 schrieb Schmitt, Michael:

[Jonathan Scott]

Please note that there is already an instruction with the
mnemonic MVCRL, "Move right to left", used to shift up data to
make a gap for inserting new data.

Jonathan Scott, HLASM
IBM Hursley, UK

[Schmitt, Michael]

Most of the assembler code I write is not required to be reentrant.

However, the specific case I was looking at yesterday IS moving from my program's storage to a GETMAIN area.

[Schmitt, Michael]

I was imagining something just like MVC except relative.

-----Original Message-----
From: IBM Mainframe Assembler List <ASSEMBL...@LISTSERV.UGA.EDU> On Behalf Of Robin Vowels
Sent: Tuesday, June 7, 2022 11:24 PM
To: ASSEMBL...@LISTSERV.UGA.EDU
Subject: Re: MVCRL

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[Steve Smith]

A Relative Long field is four bytes; obviously two would not fit into an
eight-byte instruction (there's no such thing), much less six.. A Relative
Short (to coin a term) is only two bytes, so that seems feasible, as long
as a suitable one-byte opcode is available. But then, others would want
relative to based, vice versa, and more opcodes are needed. Or, maybe
those could be defined to use a register for the length, which would allow
12-bit opcodes, which are more plentiful. The drawback is using a
register; but having variable-length MVCs would be a pretty good
compensation.

sas


On Wed, Jun 8, 2022 at 10:16 AM Schmitt, Michael <michael...@dxc.com>
wrote:

[Ngan, Robert (DXC Luxoft)]

How would you gain relative access to a getmained area, other than by editing the immediate value in the instruction after the getmain?

[Ngan, Robert (DXC Luxoft)]

Oops, didn't notice the "code is executing in getmained area" part. Doesn't that cause performance issues with Instruction/Data caches though?

[Gary Weinhold]

Only if they are in the same cache line, which are 256 bytes the last I knew.
________________________________

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[Ed Jaffe]

On 6/8/2022 6:06 AM, Jonathan Scott wrote:
> Please note that there is already an instruction with the
> mnemonic MVCRL, "Move right to left", used to shift up data to
> make a gap for inserting new data.

Destructive overlap is often quite useful (for clearing fields, etc),
but it's a PITA when you need to insert an entry into the middle of a
sequentially-organized table. I have for decades ordered such tables
backwards (in reverse address order) to facilitate better-performing
inserts using MVCL. Reverse-sequence tables are counterintuitive; harder
to understand and debug, but their use has always been worthwhile in
light of the performance gains.

The MVCRL instruction (new with z15) is only about four decades too late
for me. Still, it will be fun to be able to use it someday (if I live
that long...)


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[Martin Trübner]

Ed,

>> it will be fun to be able to use it someday (if I live that long...)

I thought the very same - but it is easier for me-


It is an excellent instruction when you need to extent an object (of a
PDF-file) in the middle. Had to use a work-area with a length of the
rest of the object-


But hey- wait a second! Why is there that silly(IMHO) restriction of
only the last byte of R0 can be the length(=256)?


Martin

[Paul Gilmartin]

On Jun 9, 2022, at 09:11:44, Ed Jaffe wrote:
>
> ... Reverse-sequence tables are counterintuitive; harder to understand

> and debug, but their use has always been worthwhile in light of the
> performance gains.
>

You needn't keep the table in reverse sequence; merely keep the unused
space at the front rather than the back.

An additional pointer reference may be necessary too get to the front.

--
gil