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From: abaum (Allen Baum)
Newsgroups: comp.arch
Subject: Re: new instructions
Message-ID: <182@armltd.uucp>
Date: 31 May 91 08:58:16 GMT
References: <12947@mentor.cc.purdue.edu>
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In article <12947@mentor.cc.purdue.edu> hrubin@pop.stat.purdue.edu (Herman Rubin) writes:

>This points out another reason for cheap instructions at little cost.  
>There are a rather large number of cases in which unsigned arithmetic
>is needed.  In fact, the EMUL description in the VAX manual even
>indicates that, for multiple precision arithmetic, this is quite
>definitely the case.
>
>Now how much additional silicon would it take to provide both signed
>and unsigned?  

I couldn't let this go by.
Herman, I accept the fact that you know far more about numerical
problems and what you need to speed them up. (Note that this is
damning with faint praise. Its easy to know more than I do)

However, you are not a hardware designer. Do not presume that because
unsigned & signed multiply are both multiplies, that including both
is cheap. It may not be the case. Boothe style mults. are implicitly
signed, for example. To pretend they aren't mean multiplying two
33 bit numbers.

This is just one example. There are others from your postings.