Math.Pow is not calculating correctly

问题

I'm having a problem with C#. To be precise with the Math.pow(). If I try to calculate 15^14 then I get "29192926025390624". But if I calculate it with Wolfram Alpha I get "29192926025390625". As you can see this only difference is 1 number. Wolfram Alpha is correct though. Why isn't C# ? and how do I fix this so I can get the correct value in C# ?7

My code is fairly simple since I'm just trying with hardcoded examples. So what I'm doing is : Math.Pow(15,14); This gives 29192926025390624. And not "29192926025390625" which is the correct answer.

Links : Wolfram Alpha

回答1:

Math.Pow operates on floating-point types, which are by definition inaccurate. If you need arbitrary precision integers, use an arbitrary precision integer type such as the BigInteger structure. BigInteger also has a Pow method.

回答2:

Math.Pow works on doubles. This implementation with long gets the correct answer:

Func<long, int, long> power = null;
power = (i, p) => p == 1 ? i : i*power(i, p - 1);
Console.WriteLine(power(15, 14));

回答3:

Math.Pow works on doubles. Doubles are 64 bit floating point and have about 15-16 digits of precision in C#, and therefore, what you are seeing is a rounding error. That is how floating point numbers work.

If you need more precision, try to use decimal. It is 128 bits and uses 10 as the base. This gives you accurate representation of numbers up to 28-29 significant digits. You can easily define your own Pow method for decimal.

If decimal is not enough, turn to BigInteger, which was added in .NET 4.

回答4:

Math.Pow() is working correctly its problem with double data type see this.

        double i = 29192926025390625;
        Console.WriteLine("{0}",i);//the result will be 29192926025390624.0

Oops Sorry, Check value by breakpoint; in your program;

回答5:

C#'s Math.pow returns a Double, an IEEE 754 standard floating point number. It only has 15 significant digits:

http://msdn.microsoft.com/en-us/library/system.math.pow.aspx http://math.byu.edu/~schow/work/IEEEFloatingPoint.htm

回答6:

What Every Computer Scientist Should Know About Floating-Point Arithmetic

来源：https://stackoverflow.com/questions/4297454/math-pow-is-not-calculating-correctly

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