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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Ada.Numerics.Big_Numbers.Big_Integer has a limit of 300 digits?
Date: Wed, 22 Dec 2021 19:48:42 +0200
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On 2021-12-22 19:27, Michael Ferguson wrote:
> On Wednesday, December 22, 2021 at 11:02:03 AM UTC-6, Luke A. Guest wrote:
>> On 22/12/2021 05:57, Michael Ferguson wrote:
>>> I just started using the Big_Integer library that is a part of the 202X version of ADA.
>>>
>>> It is repeatedly described as an "arbitrary precision library"
>>> that has user defined implementation.

Surely not "user defined"? Possibly "implementation defined".


>>> I was under the impression that this library would be able to
>>> infinitely calculate numbers of any length,

I have the same impression (up to Storage_Error, of course).


>> but there is clearly a default limit of 300 digits.
>> What are you doing that requires that number of digits?
> 
> I am working on ProjectEuler.net problem number 48.
> 
> The questions asks you to sum the numbers n^n for (2 <= n <= 1000)
> and determine what the last ten digits of this number are.
> 
> Obviously, this is quite a trivial problem when using any arbitrary
> precision library.
> 
> I had incorrectly determined that 700^700 had 300 digits, in fact
> 700^700 = 3.7E1991.
> 
> However, my code strictly breaks when the loop range is set to 683,
> which 683^683 = 8.12E1935.


How does it break? Some exception, or something else?

Mark Lorenzen suggested in an earlier post that the limit might be in 
the Big_Integer'Image function. The package 
Ada.Numerics.Big_Numbers.Big_Integers has some other output operations 
that you could try:

    function To_String (Arg : Valid_Big_Integer; ...) return String;

    procedure Put_Image (Buffer : ... ; Arg: in Valid_Big_Integer);

Of course those might be internally linked to the 'Image function and 
have the same possible limitation.