Re: [Caml-list] Comparing floats

[Boris Yakobowski <boris@yakobowski.org>]

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Indeed, thanks for the clarification...

I got confused when negating OCaml's '=' operator (a dangerous side-effect
of writing too much C!), hence the erroneous '!=' instead of <>. Regarding,
'nan <> nan', I had convinced myself that all comparisons with NaN returned
false. I wonder why <>/!= got a special treatment since e.g. 'nan < 1.' and
'1. < nan' both return false.

On Thu, Jul 23, 2015 at 5:14 PM, Jacques-Henri Jourdan <
jacques-henri.jourdan@inria.fr> wrote:

>
>
> Le 23/07/2015 13:34, Boris Yakobowski a écrit :
>
>  Hi Sébastien,
>
>  I feel obligated to point out that the _semantics_ of floating-point
> comparison is a bit tricky. IEEE 754 mandates that NaN == NaN should return
> false (as well as NaN != NaN), breaking all algebraic laws known to mankind
> :-).
>
>
> Beaware:
>
> Nan <> Nan  -> true
> Nan = Nan -> false
> Nan != Nan and Nan == Nan : depends on the memory layout.
>
>   OCaml's operators '=' and '!=' follow this convention, but  'compare
> nan nan' returns 0, which is usually the desired behavior. However,
> 'compare 0. (-0.)' also returns 0, while you might want to distinguish
> those two values.
>
>  HTH,
>
> On Thu, Jul 23, 2015 at 10:35 AM, Sébastien Hinderer <
> <Sebastien.Hinderer@inria.fr>Sebastien.Hinderer@inria.fr> wrote:
>
>> Dear all,
>>
>> What's the most efficient way to compare floats, please?
>> Is it the polymorphic compare function, or is there a more specialized
>> version of it?
>>
>> I saw Float.compare mentionned on the web but that does not seem to exist
>> any longer?
>>
>> Thanks,
>>
>> Sébastien.
>>
>> --
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>>
>
>
>
> --
> Boris
>
>
>


-- 
Boris

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