Path: utzoo!mnetor!uunet!husc6!mit-eddie!uw-beaver!cornell!rochester!PT.CS.CMU.EDU!K.GP.CS.CMU.EDU!lindsay
From: lindsay@K.GP.CS.CMU.EDU (Donald Lindsay)
Newsgroups: comp.arch
Subject: Re: Round-off
Message-ID: <623@PT.CS.CMU.EDU>
Date: 10 Jan 88 20:39:45 GMT
References: <189@mithras> <614@PT.CS.CMU.EDU> <4404@ecsvax.UUCP>
Sender: netnews@PT.CS.CMU.EDU
Organization: Carnegie-Mellon University, CS/RI
Lines: 23
Keywords: IBM HEX ???

In article <4404@ecsvax.UUCP> hes@ecsvax.UUCP (Henry Schaffer) writes:
>In article <614@PT.CS.CMU.EDU>, lindsay@K.GP.CS.CMU.EDU (Donald Lindsay) writes:
>> The floating point format normalizes to the hex digit, not to the 
>> bit level. This means that a normalized number can still have one (or two
>> or three) leading zero bits.
>> Gene Amdahl has claimed that he did this in the hope of saving hardware.
>                                                          ^^^^^^^^^^^^^^^
>This tradeoff goes back to the original 360 ...

Yes, Amdahl was the designer of the 360. My statement was based on a
statement by one of gentlemen who designed the IEEE format. He said
that he, personally, had gone into Amdahl's office and asked why. Amdahl's
answer was reportedly that he hoped to save logic in the normalization
section of FPU's.

If you read the original articles about the 360 91, you'll find mention
of the normalization hardware: IBM thought it was hot stuff.

The numeric analysis problem was actually even worse on some other machines.
For example, there was one which sometimes truncated, and sometimes
rounded - and the analyst couldn't predict which he'd get !
-- 
	Don		lindsay@k.gp.cs.cmu.edu    CMU Computer Science