[Libre-soc-bugs] [Bug 238] POWER Compressed Formal Standard writeup

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Mon Nov 30 16:04:54 GMT 2020


--- Comment #127 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Cole Poirier from comment #112)

> For what it’s worth, I just reviewEd the 16b compressed encoding page and I
> can definitely see how Alexandre came to the operating paradigm i.e. set of
> axioms interpreted from the wiki page, that he was operating under until
> this comment. 

(referring to you 3rd person, alexandre, i am aware you are there, it makes
context when answering cole easier/shorter)

what happened was: alexandre wanted to discuss alternative ideas (which i am
normally in favour of).  however one of those ideas was an "extender" that,
similar to VLE, a batch of multi-bit patterns actually indicate that the
overall length is to be 32 bit, not 16bit.

it's taken something like 3-4 days and over 60 comments to make it clear that
this idea was already eliminated right from the very start, even before
alexandre joined the discussion.

however i specifically did not say that in a categorical declarative fashion,
because if i had done that he would have been puzzled, perhaps offended, and
asked "err why?" anyway.

by instead providing explanation he has learned a huge amount in a short amount
of time particularly the difference between hardware and software.

the purpose of the wiki page is as a specification, "to be implemented" i.e. to
be frozen.

the purpose is not for said implementors to come up with, after it is frozen,
to come up with and discuss new encoding ideas!

consequently i am not going to put in a massive section emphasising that it is
16bit only.  i will mention briefly that it is not like VLE, and leave it at

with all tables throughout the entire page being exactly 16 bits on length it
should be obvious that Compressed *is* 16 bit, and i am concluding that, as
alexandre said, it was simply his *desire* to have a 32bit length in Compressed
(despite repetitions that this cannot happen) that stopped him from seeing

regarding new bugreports, i would like everyone to focus on review of the v1
Compressed, no other discussion, and once reviewed we decide what to look at
next (probably under new bugreports such as "v2 review" and so on)

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