艾伟_转载：.NET 4.0 Beta2中的BigInteger和Complex类

.NET4.0 Beta2中提供了新的System.Numerics命名空间，对应于System.Numerics.dll。该命名空间下就两个类BigInteger和Complex，我们来简单了解下
这两个类的用法。

BigInteger：任意大小的带符号整数

1.Int64, SByte, UInt16, UInt32, and UInt64这些都有一个MinValue和MaxValue属性。而BigInteger没有这两个属性，因为它没有大小限制。
2.不可变的类型.
3.由于他没有大小限制，理论上当它足够大的时候会出现OutOfMemoryException异常.

BigInteger初始化

1.我们可以使用已有的数据类型来初始化BigInteger，如下：

BigInteger bigIntFromDouble = new BigInteger(179032.6541);//会截取小点前的
BigInteger bigIntFromInt64 = new BigInteger(934157136952);

2.我们也可以使用超出现有数据类型范围的方式来得到BigInteger：

byte[] bytes = { 5, 4, 3, 2, 1 };
BigInteger number = new BigInteger(bytes);
Console.WriteLine("The value of number is {0} (or 0x{0:x}).", number); 
//The value of number is 4328719365 (or 0x102030405).   
字节数组的第一个元素为16进制的最低位，依次升高.

3.可以使用Parse或 TryParse方法将string的实例化为BigInteger：

string positiveString = "91389681247993671255432112000000";
string negativeString = "-90315837410896312071002088037140000";
BigInteger posBigInt = 0;
BigInteger negBigInt = 0;

posBigInt = BigInteger.Parse(positiveString);
Console.WriteLine(posBigInt);

BigInteger.TryParse(negativeString, out negBigInt);
Console.WriteLine(negBigInt);

4. 还可以使用静态方法Pow如下：

BigInteger number = BigInteger.Pow(Int64.MaxValue, 3);

BigInteger支持所有的数学运算，我们可以完全象使用其他整数类型一样使用BigInteger

Complex复数类

1.var z1 = new Complex(); // this creates complex zero (0, 0)
  var z2 = new Complex(2, 4);
var z3 = new Complex(3, 5);

Console.WriteLine("Complex zero: " + z1);
Console.WriteLine(z2 + " + " + z3 + " = " + (z2 + z3));

Console.WriteLine("|z2| = " + z2.Magnitude);
Console.WriteLine("Phase of z2 = " + z2.Phase);

2.我们可以使用一个ComplexFormatter类来辅助我们做格式化输出，如下：

using System;
using System.Numerics;

public class ComplexFormatter :IFormatProvider, ICustomFormatter
{
public object GetFormat(Type formatType) 
   {   
if (formatType == typeof(ICustomFormatter))
return this;
else
         return null;
   }

public string Format(string format, object arg, 
IFormatProvider provider)
   {
if (arg is Complex)
      {
Complex c1 = (Complex) arg; 
// Check if the format string has a precision specifier.
int precision;
string fmtString = String.Empty;
if (format.Length > 1) {
try {
               precision = Int32.Parse(format.Substring(1));
            }
catch (FormatException) {
               precision = 0;
            }
            fmtString = "N" + precision.ToString();
         }
if (format.Substring(0, 1).Equals("I", StringComparison.OrdinalIgnoreCase))
return c1.Real.ToString("N2") + " + " + c1.Imaginary.ToString("N2") + "i";
else if (format.Substring(0, 1).Equals("J", StringComparison.OrdinalIgnoreCase))
return c1.Real.ToString("N2") + " + " + c1.Imaginary.ToString("N2") + "j";
else
            return c1.ToString(format, provider);
      }
else
{
if (arg is IFormattable)
return ((IFormattable) arg).ToString(format, provider);
else if (arg != null) 
return arg.ToString();
else
            return String.Empty;
      }                        
   }
}

3.使用如下：

Complex c1 = new Complex(12.1, 15.4);
Console.WriteLine("Formatting with ToString():" + c1.ToString());
Console.WriteLine("Formatting with ToString(format): " +  c1.ToString("N2"));
Console.WriteLine("Custom formatting with I0:" +  String.Format(new ComplexFormatter(), "{0:I0}", c1));
Console.WriteLine("Custom formatting with J3:" +  String.Format(new ComplexFormatter(), "{0:J3}", c1));