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- Subject: Re: checking for Not a Number?
- From: Luiz Henrique de Figueiredo <lhf@...>
- Date: Thu, 21 Dec 2006 07:20:46 -0200
> Directly compairing floating point numbers for equality is *always* a bad
Only if the numbers are supposed to be the same number but are the result
of two different computations.
> For example, you can find that a floating point value which is not a
> NaN is not equal to itself.
I find this very surprising. And possibily wrong, ie against IEEE 754.
The explanation that followed made no sense to me. It would make sense for
floating point values held in *different* variables, but not for the *same*
variable. It seems to me that the gcc docs is spreading unnecessary FUD.
But I must be missing something...
> Why was the ISO C standard macro "isnan(_real-floating_ x)" not used?
Because isnan is in C99 but not in C89, which is what Lua assumes.