Then there are all of the branch relative instructions that everybody codes using the jump alias names.
-- 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 Abe Kornelis <[email protected]> Sent: Thursday, August 7, 2025 7:13 AM To: [email protected] <[email protected]> Subject: Re: Why LLC? Why not LLB? External Message: Use Caution Dave, that is a very valid question. I must admit I have no clue what drove IBM folks to choose these mnemonics over other alternatives. Chances are, there never was a conscious design decision - it's quite thinkable that it 'just happened'. Otoh, if it was a conscious and well-pondered decision after all, I doubt they'll ever bother to inform us of their musings. There are more 'peculiarities' - most of these have emerged where existing naming patterns caused new instruction mnemonics to collide with existing ones. To avoid the collision, a change in name pattern was unavoidable, but obviously the already existing mnemonics that were formed after the pattern (the one that needed changing) could not be changed with it. We are left with a hodgepodge of mnemonics that has a superficial semblance of structure only. That structure is helpful when trying to memorize mnemonics (that's what they're for, after all), but one has to know the limitations and boundaries. For the uninitiated it's a steep learning curve. Thanks for asking! Kind regards & happy programming! Abe === On 06/08/2025 21:18, David Cole wrote: > 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 >> >> ---------------------------------------------------------------------- >> For IBM-MAIN subscribe / signoff / archive access instructions, >> send email to [email protected] with the message: INFO IBM-MAIN > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
