这个VB6操作的等效C#语句创建问题

我在VB中有这个代码行：

Dim Sqrt As Double
Sqrt = Radius ^ 2 - (CenterX - X) ^ 2

上述声明中的参数正在传递以下值：

X=  -7.3725025845036161 Double
CenterX =0.0            Double
Radius= 8.0             Double

执行上述声明时，Sqrt的值为：

Sqrt    9.646205641487505   Double

现在我用Math类写了一个类似的C#逻辑：

double Sqrt = 0;
Sqrt = Math.Pow(Radius,2) - Math.Pow((CenterX - X),2);

使用相同的值集，C#代码中的输出为：

Sqrt    9.6462056414874979  double

我需要帮助，因为这个单一的C#代码更改，我的所有价值观都受到影响。有什么可以做的，以获得与* VB *源代码相似的价值？

有一个 difference in the precision between the VB6 and the .NET double type.两者都是IEEE 64位双精度类型，但.NET CLR在内部使用80位扩展精度，即您的计算在.NET中更准确。

如果您必须向下兼容VB6精度，您可以强制您的FPU(浮点单元)使用(不太准确的)64位值。这可以使用本机_controlfp_s功能实现。

以下是一个代码片段，您可以暂时“降级”浮点精度以实现向后兼容。您可以这样使用它：

用法

// default floating point precision 

using (new FloatingPoint64BitPrecision())
{
    // floating-point precision is set to 64 bit
}

// floating-point precision is reset to default

代码段

/// <summary>
/// This class changes floating-point precision to 64 bit
/// </summary>
internal class FloatingPoint64BitPrecision : Idisposable
{
    private readonly bool _resetrequired;

    public FloatingPoint64BitPrecision()
    {
        int fpFlags;
        var errno = SafeNativeMethods._controlfp_s(out fpFlags,0);
        if (errno != 0)
        {
            throw new Win32Exception(
                errno,"Unable to retrieve floating-point control flag.");
        }

        if ((fpFlags & SafeNativeMethods._MCW_PC) != SafeNativeMethods._PC_64)
        {
            Trace.WriteLine("Change floating-point precision to 64 bit");
            errno = SafeNativeMethods._controlfp_s(
                out fpFlags,SafeNativeMethods._PC_64,SafeNativeMethods._MCW_PC);

            if (errno != 0)
            {
                throw new Win32Exception(
                    errno,"Unable to change floating-point precision to 64 bit.");
            }

            _resetrequired = true;
        }
    }

    public void dispose()
    {
        if (_resetrequired)
        {
            Trace.WriteLine("Resetting floating-point precision to default");
            SafeNativeMethods._fpreset();
        }
    }
}

internal static class SafeNativeMethods
{
    [DllImport("msvcr120.dll")]
    public static extern void _fpreset();

    [DllImport("msvcr120.dll",CallingConvention = CallingConvention.Cdecl)]
    public static extern int _controlfp_s(
        out int currentControl,int newControl,int mask);

    public static int _CW_DEFAULT = 
        (_RC_NEAR | _PC_53 | _EM_INVALID | _EM_ZERODIVIDE | _EM_OVERFLOW 
        | _EM_UNDERFLOW | _EM_INEXACT | _EM_DEnorMAL);

    public const int _MCW_EM = 0x0008001f;          // interrupt Exception Masks 
    public const int _EM_INEXACT = 0x00000001;      //   inexact (precision) 
    public const int _EM_UNDERFLOW = 0x00000002;    //   underflow 
    public const int _EM_OVERFLOW = 0x00000004;     //   overflow 
    public const int _EM_ZERODIVIDE = 0x00000008;   //   zero divide 
    public const int _EM_INVALID = 0x00000010;      //   invalid 
    public const int _EM_DEnorMAL = 0x00080000;     // denormal exception mask 
                                                    // (_control87 only) 

    public const int _MCW_RC = 0x00000300;          // Rounding Control 
    public const int _RC_NEAR = 0x00000000;         //   near 
    public const int _RC_DOWN = 0x00000100;         //   down 
    public const int _RC_UP = 0x00000200;           //   up 
    public const int _RC_CHOP = 0x00000300;         //   chop 

    public const int _MCW_PC = 0x00030000;          // Precision Control 
    public const int _PC_64 = 0x00000000;           //    64 bits 
    public const int _PC_53 = 0x00010000;           //    53 bits 
    public const int _PC_24 = 0x00020000;           //    24 bits 

    public const int _MCW_IC = 0x00040000;          // Infinity Control 
    public const int _IC_AFFINE = 0x00040000;       //   affine 
    public const int _IC_PROJECTIVE = 0x00000000;   //   projective 
}