_controlfp_s metodu

Giriş
Bu metod _controlfp() metodunun daha güvenli (secure) hali.

Örnek
Şöyle yaparız

// Get control word

_controlfp_s(&cw, 0, 0); // Line A

// Enable zero-divide exception

_controlfp_s(0, ~_EM_ZERODIVIDE, _MCW_EM); // Line B

Örnek
C#'ta şöyle yaparız.. Önce metodları import ederiz.

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 
}

Sonra şöyle yaparız.

int fpFlags;
var errno = SafeNativeMethods._controlfp_s(out fpFlags, 0, 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.");
  }

}

İlk haline getirmek için şöyle yaparız.

Trace.WriteLine("Resetting floating-point precision to default");
SafeNativeMethods._fpreset();