Path: utzoo!attcan!uunet!sco!seanf
From: seanf@sco.COM (Sean Fagan)
Newsgroups: comp.arch
Subject: Re: RISC v. CISC --more misconceptions
Message-ID: <1622@scolex>
Date: 2 Nov 88 05:32:21 GMT
References: <156@gloom.UUCP> <18931@apple.Apple.COM> <40@sopwith.UUCP> <998@l.cc.purdue.edu>
Reply-To: seanf@sco.COM (Sean Fagan)
Organization: The Santa Cruz Operation, Inc.
Lines: 42

In article <998@l.cc.purdue.edu> cik@l.cc.purdue.edu (Herman Rubin) writes:
>Maybe we should have a "competition" to see how many operations
>we can come up with for which silicon can do a quick, efficient, accurate job,
>but which are clumsy and expensive in software.
>	Find the distance to the next one in a bit stream FAST.  It would
>be good to have an exception handler if one is not found.  I am considering
>algorithms not worth implementing if the operation is slow.
>	Divide an integer by an integer, obtaining a quotient and a remainder,
>the choice of remainder depending on the signs of the dividend and the divisor.
>	Divide a floating point number by a floating point number, obtaining
>an integer quotient and a floating point remainder.  It would be nice to have
>the choice of remainder depending on the signs here also.

Quick background:  Cyber 170's have 24 regsiters: A, B, and X, eight of each
(0-7).  A and B registers are 18 bits wide, and are, generally, used for
address variables.  X registers are 60-bits wide, and are usually used for
computation.  To load a value into X<n>, you load the address into A<n>,
where n=[1,5].  To store a value from X<n>, you load the address into A<n>,
where n=[6,7].  A0 has no special values, and B0 is a hardwired 0.

Ok, a few from the Wonderful World of the Cyber:

	Count the set bits in a word (register or memory, it doesn't
matter).  Very useful for some trivial applications (such as playing
Othello), but I haven't seen much else done with it.  It was put in, it
looks like, because the hardware was already there (in the form of parity
checking), but I could be wrong.

	Given the, um, interesting setup described above, write a routine to
save all of the registers into memory (hint:  use shifts).  It ain't easy,
and I don't remember how to do it, so don't mail me 8-).  It is, however,
trivial to do in hardware.


Who else has some fun examples?

>Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907

-- 
Sean Eric Fagan  | "Engineering without management is *ART*"
seanf@sco.UUCP   |     Jeff Johnson (jeffj@sco)
(408) 458-1422   | Any opinions expressed are my own, not my employers'.