Path: utzoo!utgpu!water!watmath!clyde!rutgers!cmcl2!husc6!uwvax!umn-d-ub!umn-cs!ems!pwcs!eta!como!rpeglar
From: rpeglar@como.lake.eta.com (Rob Peglar)
Newsgroups: comp.arch
Subject: Re: single vs double float
Summary: more history of 64-bit single
Keywords: CDC,Cray,precision,floating
Message-ID: <181@como.lake.eta.com>
Date: 8 Feb 88 17:01:46 GMT
References: <235@unicom.UUCP> <28200089@ccvaxa> <3127@phri.UUCP> <408@micropen> <10420@mimsy.UUCP> <790@PT.CS.CMU.EDU>
Reply-To: rpeglar@como.UUCP (Rob Peglar)
Distribution: na
Organization: The Final Frontier
Lines: 23
Posted: Mon Feb  8 11:01:46 1988

In article <790@PT.CS.CMU.EDU> abh@POGO.CAMELOT.CS.CMU.EDU (Andrew Hastings) writes:
>In article <10420@mimsy.UUCP>, chris@mimsy.UUCP (Chris Torek) writes:
>in 1976.  The CRAY C compiler treats `double' as `float' (i.e., floating
>arithmetic is performed in single precision) since double precision is
>about an order of magnitude slower than single precision on these machines.
>an order of magnitude slower.
>
>-Andrew Hastings		abh@cs.cmu.edu			412/268-8734

You're right.

The CDC Star-100 series of the late 60's/early '70s also had 64-bit single
precision.  Due to the VERY large instruction set, they also could do double
precision (128-bit results) at a ratio of 5 or 6:1 versus single.  That  
figure just counts the cycles involved in the add lower/upper, normalize,
etc etc instructions used to do double precision.

BTW, ETA C also treats 'double' as 'float'.


Rob Peglar

The above is my opinion, not that of my employer.  (the usual)