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From: peterf@arp.anu.oz.au (Peter Fletcher)
Newsgroups: comp.lang.c
Subject: Why do most C compilers poxily round towards zero ?
Message-ID: <1990Oct9.230928.27552@arp.anu.oz.au>
Date: 9 Oct 90 23:09:28 GMT
Organization: Automated Reasoning Project, ANU.
Lines: 47

One of the most frustrating things about using floating point in C is the
poxy way rounds floating point numbers towards zero instead of -infinity.

This creates a big inconsistency around 0.0 and makes any sort of consistent
rounding a bigger hassle than you'd like:

To round a number, instead of

	int a;
	float b;
	...
	a = (int)(b+0.5);

you need to do

	a = (b>0.0) ? (int)(b+0.5) : (int)(b-0.5);

Worse, to floor a number, instead of

        a = (int)b;

you need to do either

	a = floor(b); or
	a = (b>0.0) ? (int)b : -(int)(-b);

Also, you have silly situations where

	(int)(b-10.0)+10 doesn't always equal (int)b

I don't think this policy is in any of the C specifications, but it occurs
in all the C compilers I've used (sun, apollo, pyramid).  Does anyone know
why ?

I think with Suns and Apollos you can tell the floating point hardware
to use a different rounding mode, but it seems that both methods are
completely different and probably not compatible with anybody else.
Is there a reasonably standard Unix way to do this ?

-peter fletcher 
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