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From: haynes@felix.ucsc.edu (99700000)
Newsgroups: comp.arch
Subject: Re: condition codes
Message-ID: <15909@darkstar.ucsc.edu>
Date: 17 May 91 05:06:16 GMT
References: <12162@mentor.cc.purdue.edu> <13011@pt.cs.cmu.edu> <12236@mentor.cc.purdue.edu>
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Organization: University of California, Santa Cruz Open Access Computing
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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.
>
Well if we could go back to the Burroughs B5500 of 1964 vintage we
wouldn't have.  An integer on that machine was simply a floating point
number with a zero exponent; the hardware algorithms tried to keep the
exponent zero as long as possible, rather than always normalizing.
The only type conversion instruction was one that would integerize a
float when an integer value was required.  I believe the concept
actually goes back to Householder of Oak Ridge in the 1950s.

But in that same year of 1964 IBM unleashed its new 360 line on the
world; and one of the features of that product was that for some
models floating point was an extra-cost option, requiring that microde
and perhaps hardware be added to the machine.  So I guess they made a
floating point feature that could be strapped on the side of the
basic machine without much disturbance to it.

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.)
-- 
haynes@cats.ucsc.edu
haynes@ucsccats.bitnet

"Any clod can have the facts, but having opinions is an Art."
        Charles McCabe, San Francisco Chronicle