Calculating big float number fast like 0.4 ^ 100000000 ,, any ideas?

问题

Ehm ... I got a problem I've a certain calculation that result is over 10^-308 (the biggest value in double .net ) any way I solved this problem through a library called BIGFLOAT http://www.fractal-landscapes.co.uk/bigint.html ,

What ever I need to calculate something like 0.4 ^(1000 or 100000000) the problem it takes very very long time I didn't study parallel or distributed programming yet but I need a solution that is fast and understandable for me I'm going to deliver this project in next 6 Hours!! :D

Here's the code :

private BigFloat getBlocking(double k)
    {
        double p1, p2;
        BigFloat p3;
        p3 = new BigFloat(pp);
        p1 = this.P / (double)(k / (double)this.N);
        p2 = Math.Pow((1 - p1), 2);
        p3= new BigFloat(1-p2,pp);
        p3.Pow((int)k);
        return p3;

    }

where K is 1000 , N is 1001

回答1:

Download, and reference, the Microsoft J# .NET Library from your C# project - so that you can use J#'s BigDecimal implementation.

See:

Arbitrary-Precision Decimals in C#

Big Decimal:

Install the J# runtime (it's free): http://www.microsoft.com/downloads/en/details.aspx?familyid=f72c74b3-ed0e-4af8-ae63-2f0e42501be1&displaylang=en

and:

Arbitrary precision decimals in C#?

and:

http://geekswithblogs.net/gyoung/archive/2006/05/01/76869.aspx

The J# re-distributables contain very well tested implementations of BigInteger and BigDecimal that you can use directly in your .NET apps simply by referencing the J# assembly vjslib.dll. http://download.microsoft.com/download/2/e/9/2e9bde04-3af1-4814-9f1e-733f732369a3/NETMatters0512.exe discusses this further. It also contins some Zip classes which are quite useful.

and:

MSDN - BigInteger, GetFiles, and More

While you can search the Web to find a plethora of implementations in C#, C++, and a variety of other languages, it might not be necessary. If you don't mind taking a dependency on the J# libraries, you already have a big number implementation at your disposal. In fact, you have two. The J# run-time library, vjslib.dll, is available as a redistributable component, just like the .NET Framework. You can download it from Visual J# Downloads (it's also installed as a prerequisite by Visual Studio®). In the same manner that a C# or C++ application can make use of Microsoft.VisualBasic.dll (the Visual Basic run-time library), C#, Visual Basic®, and C++ applications can use the J# run-time library and the numerous interesting classes it exposes.

回答2:

If you don't need all the digits, you can get away with using logarithms. The log of (0.4 ^ 100000000) is log(0.4)*100000000, well within the regular floating point range.

来源：https://stackoverflow.com/questions/5738309/calculating-big-float-number-fast-like-0-4-100000000-any-ideas

标签

performance

bigint

computation

bigfloat