_controlfp does not prevent DivideByZeroException

我用c#写了以下几行

using System;
using System.Runtime.InteropServices;
namespace ConsoleApplication1
{
    class Program
    {
        [DllImport("msvcrt.dll", CallingConvention = CallingConvention.Cdecl)]
        extern static uint _controlfp(uint newcw, uint mask);
        const uint _MCW_EM = 0x0008001f;
        public const uint EM_INVALID = 0x00000010;
        public const uint EM_DENORMAL = 0x00080000;
        public const uint EM_ZERODIVIDE = 0x00000008;
        public const uint EM_OVERFLOW = 0x00000004;
        public const uint EM_UNDERFLOW = 0x00000002;
        public const uint EM_INEXACT = 0x00000001;
        static void MaskFpu(uint pExceptionMask = EM_INVALID)
        {
            // add desired values
            _controlfp(_MCW_EM, pExceptionMask);
        }
        static void Main(string[] args)
        {
            MaskFpu(EM_ZERODIVIDE);
            int a = 0;
            var b = 5/a;
            Console.WriteLine("b = " + b);
        }
    }
}

Main方法从设置控制字开始。显然，我希望DivideByZeroExceptions被屏蔽。

在执行_controlfp之后，我希望除零将返回NaN。但是var b = 5 / a会抛出一个异常。

我如何才能真正保持我的进程从引发DivideByZeroExceptions?

int a = 0;
var b = 5/a;