Re: 1 - 1, 1 -1, 1-1, 1 - -1 and -2147483648

On 31 Jan 2006 09:57:37 -0500, Edsko de Vries wrote:


[...]
> Is there a good solution that solves both problems? At the moment, I
> have added a new rule to the lexer that matches this exact number,
> which solves the problem - but it's a hack.. (actually, there are two
> rules, one for 32-bit machines, one for 64-bit machines..)


In Ada all literals are considered of some indefinite numeric type
[Universal_Integer]. The compiler evaluates all expressions exactly and
generates error when the result is converted to the target [finite] type.
So, for example, if Int_8 has range -128..127, nevertheless the following
is legal Ada:


      X : Int_8 := 1000 - 900; -- The result is in the range


With this approach, literals are unsigned and unary minus works just fine.


Of course, you will not be able to compile something like


      2**98756466 - 2**98756466


which is also legal. But it is not a big loss. (:-))


--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

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