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Date: Sat, 16 Mar 2002 21:32:04 +0100
From: Damien Carbonne <damien.carbonne@free.fr>
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Subject: Re: Why raises this an error? :-(
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Date: 2002-03-16T21:27:12+01:00
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Kai Gl�sner a �crit :

> Hello community,
>
> while porting an c++ math-library to Ada95 (Gnat 3.12p under Linux) I
> experienced:
>
> This:
>
>     Alt_D := (-8.0/4.0) ** 2.0;
>
> raises this:
>
>     raised ADA.NUMERICS.ARGUMENT_ERROR : a-ngelfu.adb:111 instantiated
> at a-nuelfu.ads:20
>
> This:
>
>     Alt_D := -2.0 ** 2.0;
>
> works fine!
>
> Why? What have I overlooked here... :-/
>
> Thanks in advance for an answer...
>
> Kai Glaesner

I am not completely sure, but there may be a precedence issue here.
I think -2.0**2.0 is equivalent to -(2.0**2.0)
whilst (-8.0/4.0)**2.0 is equivalent to (-2.0)**2.0.
There is no general interpretation to the power of a negative number (except
when the power is an integer value)
Anyway, if what you need is the squarre value of a number, I think a simple
multiplication is much faster than a general exponentiation algorithm.

Regards

Damien carbonne