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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.lang.c
Subject: Re: derived types
Message-ID: <4987@utzoo.UUCP>
Date: Tue, 29-Jan-85 19:06:51 EST
Article-I.D.: utzoo.4987
Posted: Tue Jan 29 19:06:51 1985
Date-Received: Tue, 29-Jan-85 19:06:51 EST
References: <7479@brl-tgr.ARPA> <37@gitpyr.UUCP>, <6873@watdaisy.UUCP>
Organization: U of Toronto Zoology
Lines: 24

> > If I were to adapt C to the 170 series, I would set the following types:
> > 
> > 	float			60-bits
> > 	double			60-bits
> 
> Don't you dare.  Double doesn't have to be exactly twice a float, but there
> has to be enough to assist numerical calculations in certain kinds of error
> determinations.

Sorry, even tired old K&R says (section 4):

	Single-precision floating point (float) and double-precision
	floating-point (double) may be synonymous in some implementations.

This really is inevitable on machines that don't gracefully support a
short floating-point type.  Making float == double really is the right
thing to do when the shortest floating-point type is adequate for
normal use, i.e. 64 bits or thereabouts.  Making double a longer type
generally means a severe speed penalty for all arithmetic, unless the
compiler is new enough to take advantage of the ANSI draft's permissive
language on this point.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry