Re: comparing doubles for equality

Thad Smith wrote:
John Smith wrote:

This code for the comparison of fp types is taken from the C FAQ.
Any problems using it in a macro?

/* compare 2 doubles for equality */
#define DBL_ISEQUAL(a,b) (fabs((a)-(b))<=(DBL_EPSILON)*fabs((a)))

This construction is misleading and I would never use it, because
the implied function, determining whether two doubles are equal,
is not an accurate description of the returned value.

How about:

#define DUNEQUAL(a, b) (fabs((a)-(b)) > (DBL_EPSILON)*fabs((a)))

with a caveat against passing an a with side effects.

--
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Joyeux Noel, Bonne Annee.
Chuck F (cbfalconer at maineline dot net)
<http://cbfalconer.home.att.net>


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