Re: Implementing Memorize

[Marius Amado Alves <amado.alves@netcabo.pt>]

On Wed, 2003-10-22 at 11:33, Lutz Donnerhacke wrote:
> * Lutz Donnerhacke wrote:
> > Calculating Fibbonacci numbers recursivly is easy but braindead. Languages
> > with access to the symbol table at execution time are able to change the the
> > reccuring call with a memorize wrapper which returns already computed values
> > immediatly instead of recalculating them. In the referenced article I wrote
> > an C-Implementation of such a wrapper. Now I'm looking for a more elegant
> > version in Ada.

So your problem is generating the Fibonaci number of a given natural N.

I would not use recursive calls here because call stack space is usually
shorter than the range of naturals. I would use increments in a loop.
And I think I would use a precomputed table of values for N = 100,
200... (say). And it is clear that Fib (Natural'Last) is much bigger
than Natural'Last so I would look for the M such that Fib (M) <=
Natural'Last and Fib (M + 1) > Natural'Last and then constrain the input
type to 0 .. M. Or else use a big numbers package for the output type.

> ...

Took a look at your code. I think you're failing to set the Valid
component.