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From: hrubin@pop.stat.purdue.edu (Herman Rubin)
Newsgroups: comp.arch
Subject: Integer/floating
Message-ID: <12451@mentor.cc.purdue.edu>
Date: 17 May 91 11:41:10 GMT
Article-I.D.: mentor.12451
References: <12162@mentor.cc.purdue.edu> <13011@pt.cs.cmu.edu> <15909@darkstar.ucsc.edu>
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In article <15909@darkstar.ucsc.edu>, haynes@felix.ucsc.edu (99700000) writes:
> 
> In article <12236@mentor.cc.purdue.edu> hrubin@pop.stat.purdue.edu (Herman Rubin) writes:
> >
> >Why do we have separate integer and floating units, especially without 
> >communication between them?  I suggest those who push this horror look
> >at how difficult conversion between them is.  I have already pointed out
> >that every trigonometic and exponential routine does, in some way, 
> >float/float -> integer, remainder.  The integer is also used.

			....................

> Now that we have a floating point standard that requires almost always
> normalizing I guess we can never go back to where we were in 1964.
> (Burroughs - er, ah, Unisys - is still making machines with the old
> number representation, but they must be mightly lonely.)

They are not the only ones; the CYBER 205/ETA 10 and the CRAYs still
have it.  Even the 360 and its descendents, which do not have integer/
floating communication, do not (and in this case cannot)have forced
normalization.

Is the 1-bit gain from forced normalization worth the other problems?
For example, without it, the RS/6000 would be capable of reasonable
52x52 -> 104 multiplication in its floating unit, with addition 
included, especially if a quick add-to-exponent operation were 
included.  Oops, that would require communication between the
integer and floating unit; so let's make that add-to-exponent 
immediate.

Versatility cannot be easily added after the design, but it can be
before.
-- 
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907-1399
Phone: (317)494-6054
hrubin@l.cc.purdue.edu (Internet, bitnet)   {purdue,pur-ee}!l.cc!hrubin(UUCP)