[Vm-dev] failing/errors Pharo Tests with CogVM

[Eliot Miranda]

On Thu, Sep 16, 2010 at 10:54 PM, Andreas Raab <andreas.raab at gmx.de> wrote:

>
> On 9/16/2010 2:44 PM, Eliot Miranda wrote:
>
>>     I realise we need to be more precise.  Are you talking about NaNs
>> specifically or NaN and Inf?
>>
>
> NaN only. +-Inf are fine as they have a well-defined mathematical
> relationship over the set of numbers. NaN does not.
>
>
>  The Squeak VM happily answers Inf from its
>> float primitives.  In fact the only guard against a NaN or Inf result
>> being produced by the floating-point primitives is the guard against
>> dividing by zero.  But e.g. in the interpreter (1.0e300 / 1.0e-300)
>> isInfinite and there is no failure.  So specifically failing for aFloat
>> / 0.0 seems a bit of a fig leaf to me.
>>
>> So what would your ideal semantics be?
>> a) - fail whenever the result is Inf or NaN?
>> b) - fail whenever the result is NaN and allow aFloat / 0.0 to answer Inf
>> c) - fail whenever the result is NaN but fail aFloat / 0.0
>> d) - the Interpreter status quo, fail only for aFloat / 0.0
>> e) - never fail and answer Nan and Inf as specified in IEEE 754
>>
>> The situation with VW before IEEE was that it did a) and we changed it
>> so that the mode switch selected either a) or e), with, IIRC, the
>> current default being e).
>>
>
> f) Fail whenever the result is NaN or when dividing by zero.
>

OK, to be pedantic that's c) above.  But fine. This is a reasonable choice.


> My preference for f) is that division by zero should be consistent between
> floating point numbers and integers. It would be strange if "1 / 0" => boom
> but "1.0 / 0" => Inf or "1 / 0.0" => Inf. *However* underflow isn't division
> by zero and may silently result in Inf. In other words:
>
>        self should:[1.0 / 0.0] raise: ZeroDivide.
>
> but (#successor produces the smallest float larger than the receiver)
>
>        self shouldnt:[1.0 / 0.0 successor] raise: Error.
>        self assert: (1.0 / 0.0 successor) = Float infinity.
>
> Cheers,
>  - Andreas
>
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