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From: eck@cs.vu.nl (Hans van Eck)
Newsgroups: comp.std.c
Subject: Re: floating point constant folding
Message-ID: <8237@star.cs.vu.nl>
Date: 14 Nov 90 08:58:32 GMT
References: <8191@star.cs.vu.nl> <1990Nov13.174025.1520@zoo.toronto.edu>
Sender: news@cs.vu.nl
Lines: 33

henry@zoo.toronto.edu (Henry Spencer) writes:

>In article <8191@star.cs.vu.nl> eck@cs.vu.nl (Hans van Eck) writes:
>>Is it allowed to evaluate constant floating point expressions with greater
>>range and precision than that of the execution environment in contexts
>>where a constant is not required?

>I believe the relevant statement is the "as if" rule discussed in 2.1.2.3:
>the compiler can do anything it pleases, provided the observable results
>are the same.  Observable results include overflow exceptions and the values
>of data items written out to files.  Evaluating constant floating-point
>expressions at compile time using different floating-point hardware strikes
>me as a minefield of difficulties.

The problem is that the standard (in 3.4) explicitely allows greater range
and precision for floating point expressions when a constant is required,
which seems to take higher precedence than the "as if" rule.  What I do not
know is whether this rule may also be applied when a constant is not
required.

Perhaps a simple example is in place:

	{ static double d = 0.3F;
		 double e = 0.3F;

In this example, d may may be initialised with a precision higher than that
of a float.  Does that also hold for e?

Thanks in advance.
--
Hans van Eck, Dept. of Mathematics and Computer Science, Vrije Universiteit,
De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
Voice: +31 20 5485302 			Email:	eck@cs.vu.nl