Path: utzoo!utgpu!water!watmath!clyde!rutgers!cmcl2!husc6!sri-unix!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.arch
Subject: Re: Round-off
Summary: "decimal" float
Message-ID: <524@cresswell.quintus.UUCP>
Date: 12 Jan 88 20:44:32 GMT
References: <189@mithras> <614@PT.CS.CMU.EDU> <4404@ecsvax.UUCP> <4412@ecsvax.UUCP>
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 20

In article <4412@ecsvax.UUCP>, hes@ecsvax.UUCP (Henry Schaffer) writes:
> circuitry is the conjunction of economics with engineering/physics.  If we
> had good deci-stable devices (cf. bi-stable) then we could have computers
> which were internally decimal - and that would be preferable.  I would hope
> that numerical analysts could deal with such computers.   Humph!  :-)

There was an article in the Australian Computer Journal sometime in the
early 70s which described a method where a BINARY computer could provide
DECIMAL floating point.  {The exponent and significand would be binary
numbers, but the base was 10.}  It was claimed that the hardware for this
would not be more complex than the hardware for base 8 (Burroughs main-
frames) or for base 16 (IBM).  The method was implemented in software
for a student BASIC system written at the University of Auckland.  The
big advantage of binary-but-base-10 floating point is that there is NO
conversion error due to change of base: if you write 0.1, you get 0.1
exactly.  Output conversion is also exact.

Didn't some models of the /360 truncate rather than rounding, or fail
to use guard digits, or something of that sort?  None of the numerical
analysis courses I ever took told me that (x*2)/2 had to equal x.