Ada中的任意长度整数 [英] Arbitrary length integer in Ada

问题描述

我目前正在自学Ada，尽管我可以从解决一些较常规的问题开始入手。

I am currently teaching myself Ada and though I could begin by tackling some of the more conventional problems to get started.

更具体地说，我尝试计算阶乘n ！，而n> 100。到目前为止，我的实现是：

More specifically I try to calculate the factorial n!, whereas n>100. My implementation so far is:

with Ada.Text_IO;
with Ada.Integer_Text_IO;

use Ada.Text_IO;

procedure Factorial is 
    -- define a type covering the range beginning at 1 up to which faculty is to
    -- be computed.
    subtype Argument is Long_Long_Integer range 1..100;

    -- define a type that is large enough to hold the result
    subtype Result is Long_Long_Integer range 1..Long_Long_Integer'Last;
    package Result_IO is new Ada.Text_IO.Integer_IO(Result); use Result_IO;

    -- variable holding the faculty calculated.
    fac : Result := 1;

begin
    -- loop over whole range of ARGUMENT and calculate n!
    for n in ARGUMENT loop
        fac := (fac * n);
    end loop;
end;

问题显然是，即使Long_Long_Integer对此也可能太小，并为n>引发CONTRAINT_ERROR异常20。

The problem is obviously that even Long_Long_Integer is may too small for this and throws a CONTRAINT_ERROR exception for n>20.

是否有一个实现任意大小整数的包？

Is there a package that implements arbitrary-sized integers?

谢谢！

PS：我确实选择不使用递归，因为我想探索此练习中的循环。但是，否则请对代码的所有方面（样式，最佳实践，错误..）进行评论。

PS: I did opt against recursion because I wanted to explore loops in this exercise. But otherwise please comment on all aspects of the code (style, best-practices, error..)

推荐答案

Ada加密库支持无符号大数字（ Big_Numbers ）。您可以从 http://sourceforge.net/projects/libadacrypt-dev/下载
库。
我建议您检查svn。当前版本的Big_Numbers乘法函数
有一个小错误。

The Ada Crypto Library supports big unsigned numbers (Big_Numbers). You can download the lib from http://sourceforge.net/projects/libadacrypt-dev/. I recommend checking out the svn. The Big_Numbers multiplication function of the current release has a minor bug.

您可以使用当前的GNAT编译器从 AdaCore Libre网站。

You can compile the lib with the current GNAT compiler from the AdaCore Libre site.

lib无法在gcc下编译-4.3或gcc-4.4，因为 gcc中的错误。

The lib will not compile under gcc-4.3 or gcc-4.4 because of a bug in gcc.

最后，我将举一个小例子，说明如何将LibAdaCrypt中的两个512位Big_Numbers
相乘。

Finally, I will give you a small exmple how to multiply two 512-bit Big_Numbers from the LibAdaCrypt.

package Test.Big_Numbers is

with Crypto.Types.Big_Numbers;

pragma Elaborate_All(Crypto.Types.Big_Numbers);

package Big is new Crypto.Types.Big_Numbers(512);
    use Big;
    use Big.Utils;
end Test.Big_Numbers;



package body Test.Big_Numbers is

x : Big_Unsigned := To_Big_Unsigned("16#57C19F8F7866F8633AC1D25B92FC83B4#");
Y : Big_Unsigned := To_Big_Unsigned("16#FFFFFFFFFFFFFFFFFFFFFFFFFFFFFF60#");

x := X * Y;
Put_Line(X);

end Test.Big_Numbers;

 
Best regards
   Christian

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