Re: Reproducibility of minNum() and maxNum() for decimal

[Peter Henderson <petercbh@xxxxxxxxxxx>]

Michel Hack wrote:
> Here is something that we should have noticed months ago... but I
> only realised this when David Hough wrote "except for minNum() ..."
> in a draft of a possible revision of Clause 10.
>
> The definition allows either operand to be returned when both are
> numeric and compare equal, i.e. have the same value.
>
> In the case of decimal, this implies that the quantum of the result
> is implementation-dependent in the case of equal values but different
> quanta.
>
> This effect is observable with the sameQuantum() predicate, and this
> is a problem for the "reproducible results" section, and a few other
> places that mention "equal results".
>
> There may also be an effect on signaling Invalid -- a flag that is
> supposedly reproducible -- because quantize(x,y) may signal Invalid
> depending on the quantum of y.
>
> The easiest fix would be to require that minNum() and maxNum() return
> the first operand in case of numerical equality, at least in decimal,
> so as to avoid this unpredictability.
>   
I feel it would be preferable to return the operand with the maximum 
quantum. In this way, these functions are commutative.  Returning the 
operand with the maximum quantum avoids attaching undeserved precision 
to the result.

Regards,
Peter Henderson