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);
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：
// 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
}