OK, bad example. I'm stuck on a z9BC, likely until the end of the current age
of computing (tentatively scheduled for 21 Dec 2012, I've been told). I had
forgotten about those. So, how about to prevent a division by zero condition?
CP DIVISOR,=P'0'
EXNZ
DP DIVIDEND,DIVISOR
But I'm likely being ridiculous. It is likely easier to simply use branch
instructions. Gotta quit reading the RISC and ARM manuals. They give me strange
notions.
I was even thinking it might be "interesting" to have what I think of as a
"tentative execution" instruction. It is like the EX, but suppresses the EX'd
instruction if it gets a "program interrupt" instead of causing a "program
interrupt" and invoking the FRR/ESTAE type exits. Of course, detecting that
this might be a bit iffy.
--
John McKown
Systems Engineer IV
IT
Administrative Services Group
HealthMarkets(r)
9151 Boulevard 26 * N. Richland Hills * TX 76010
(817) 255-3225 phone *
[email protected] * www.HealthMarkets.com
Confidentiality Notice: This e-mail message may contain confidential or
proprietary information. If you are not the intended recipient, please contact
the sender by reply e-mail and destroy all copies of the original message.
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MEGA Life and Health Insurance Company.SM
> -----Original Message-----
> From: IBM Mainframe Assembler List [mailto:ASSEMBLER-
> [email protected]] On Behalf Of Robert Ngan
> Sent: Monday, November 26, 2012 4:01 PM
> To: [email protected]
> Subject: Re: Stupid? though on a new "execute" instruction.
>
> You mean like LOAD ON CONDITION and STORE ON CONDITION?
>
> They were added in the 9th edition of the POPS.
>
> Robert Ngan
> CSC Financial Services Group
>
>
>
> From: "McKown, John" <[email protected]>
> To: [email protected]
> Date: 2012/11/26 15:39
> Subject: Stupid? though on a new "execute" instruction.
> Sent by: IBM Mainframe Assembler List <ASSEMBLER-
> [email protected]>
>
>
>
> It's the holiday season. So be nice.
>
> There currently exist 2 execute variants. The old base+displacement and
> the new relative. Now that we have 64 bit registers, why not have an RR
> instruction where the first register the modifying value but the second
> register contains the actual instruction to be executed. I have no idea
> how the hardware actually works internally, so perhaps this would be a
> huge kludge. But, then, at present the EX instruction must copy the
> referenced instruction "somewhere" and modify it "somehow". So why
> couldn't it copy from a register as well as from the D-cache? Or,
> maybe, how about an EX which works like EXRL but the relative
> instruction is "hard coded" to be the next instruction in line? The
> problem, of course, is that this new EX would then need to "skip over"
> the just executed instruction. And I don't know how to handle
> "interruptible" instructions. But EX can do it, so I guess the same
> way.
>
> Yes, I realize these are likely not of much importance. It's just that
> there's nothing going on and for the rest of the year we are in "don't
> do anything" mode so that month-end, quarter-end, and year-end
> processing will be smooth.
>
> OK, since I have you here anyway. What about a real weirdie? An
> instruction which says whether or not to execute the next instruction,
> based on the condition code? That would enable every instruction to be
> a conditional instruction. Perhaps EXNC (Execute Next Conditional).
> What comes to mind?
> Perhaps:
> SLR R2,R2
> LTR R1,R1
> EXNC NZ
> L R2,0(,R1)
> LTR R2,R2
> JZ BADADDR
> Which would load the contents of R2 with the address contained in R1
> unless it was zero. Or maybe (combining both of the above)
> L R1,LEN LENGTH OF FIELD
> AHI R1,-1 DECREMENT FOR EX
> EXNZ
> EXRI R1 EX NEXT INSTRUCTION
> MVC RECEIVE(0),FROM
>
> Returning you now to your regularly scheduled, useful, email.
>
> --
> John McKown
> Systems Engineer IV
> IT
>
> Administrative Services Group
>
> HealthMarkets(r)
>
> 9151 Boulevard 26 * N. Richland Hills * TX 76010
> (817) 255-3225 phone *
> [email protected] * www.HealthMarkets.com
>
> Confidentiality Notice: This e-mail message may contain confidential or
> proprietary information. If you are not the intended recipient, please
> contact the sender by reply e-mail and destroy all copies of the
> original message. HealthMarkets(r) is the brand name for products
> underwritten and issued by the insurance subsidiaries of HealthMarkets,
> Inc. -The Chesapeake Life Insurance Company(r), Mid-West National Life
> Insurance Company of TennesseeSM and The MEGA Life and Health Insurance
> Company.SM
