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From: bzs@bu-cs.BU.EDU (Barry Shein)
Newsgroups: net.arch
Subject: Re: Floating point performance
Message-ID: <1965@bu-cs.bu-cs.BU.EDU>
Date: Sat, 18-Oct-86 19:22:26 EDT
Article-I.D.: bu-cs.1965
Posted: Sat Oct 18 19:22:26 1986
Date-Received: Tue, 21-Oct-86 21:00:32 EDT
Organization: Boston U. Comp. Sci.
Lines: 23



From: nather@ut-sally.UUCP (Ed Nather)
>Has hardware technology progressed to the point where we might want to
>consider making a VERY LARGE integer machine -- with integers long
>enough so floating point operations would be unnecessary?

Why wouldn't the packed decimal formats of machines like the IBM/370
be sufficient for most uses (31 decimal digits+sign expressed as
nibbles, slightly more complicated size range for multiplication and
division operands, basic arithmetic operations supported.) That's not
a huge range but it's a lot larger than 32-bit binary. I believe it
was developed because a while ago people like the gov't noticed you
can't do anything with 32-bit regs and their budgets, and floating
point was unacceptable for many things. There are no packed decimal
registers so I assume the instructions are basically memory-bandwidth
limited (not unusual.)

The VAX seems to support operand lengths up to 16-bits (65k*2 digits?
I've never tried it.) There is some primitive support for this (ABCD,
SBCD) in the 68K.

	-Barry Shein, Boston University