Seymour,
I just grabbed my 2022 Reference Summary and looked at the chart. There
are so many patterns, yet several exceptions.
I can just hear a hardware person saying:
"I can add the function to the chip, but you will need to add more
letters to the alphabet before we can give it a mnemonic."
I wonder if the hardware guys assign the mnemonic, or if the assembler
developers assign it? (Based on some of the names, I am betting the
hardware guys.)
Tony Thigpen
Seymour J Metz wrote on 8/8/25 6:40 AM:
And R was register.
So besides B, G, H, I, L, R, and Y, what other letters have new meaning?
--
Shmuel (Seymour J.) Metz
http://mason.gmu.edu/~smetz3
עַם יִשְׂרָאֵל חַי
נֵ֣צַח יִשְׂרָאֵ֔ל לֹ֥א יְשַׁקֵּ֖ר
________________________________________
From: IBM Mainframe Discussion List <[email protected]> on behalf of Tony
Thigpen <[email protected]>
Sent: Friday, August 8, 2025 1:38 AM
To: [email protected] <[email protected]>
Subject: Re: Why LLC? Why not LLB?
External Message: Use Caution
I just look at it from this view:
Normally, 'C' in an instruction mnemonic indicates character actions,
not numeric actions. 'P' indicated packed decimal actions. And, the
absence of such indicated the default numeric actions.
(At least, before all the new stuff.)
So, for numeric, it was 'L' was a fullword, and 'LH' is a halfword' and
'LB' for a byte. It could just as easily been Load Numeric ('LN', 'LHN'
and 'LBN') but the original designers did not go that way. Maybe for
less keystrokes on punch cards because these were the more common
instructions used?
Tony Thigpen
David Cole wrote on 8/6/25 3:18 PM:
I apologize is my initial post was unclear. My question is about IBM's
choice of instruction names, not about functionality.
Also, this has nothing whatsoever to do with the C language.
Let me edit my post and re-present it here...
In Principles, these two machine instructions are presented:
- LB loads a byte into a register and sign-extends it.
- LLC also loads a byte into a register but then zero pads it.
That's all pretty clear, but...
My question is, why did IBM choose have the instruction's name end with
B in one case and with C in the other?
- On the one hand, Why didn't they choose LC (instead of LB) as
that instruction's name?
- Or on the other, why didn't they choose LLB (instead of LLC) as
that instruction's name?
Just curious.
Dave Cole
At 8/6/2025 05:42 AM, David Cole wrote:
In Principles:
- LB loads a byte into a register and sign-extends it.
- LLC also loads a byte into a register but then zero pads it.
That's all pretty clear, but...
Why use B in one case and C in the other?
- Why not LC instead of LB?
- Or why not LLB instead of LLC?
"Inquiring minds what to know."
Dave Cole
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