System.Set8087CW Function

Sets both the control word in the floating point unit and the variable NoErrMsg declared in the system unit.

Pascal

procedure Set8087CW(NewCW: Word);

C++

Set8087CW(Word NewCW);

File

System

Description

The floating-point unit control word controls the precision of floating point calculations, the rounding mode, and whether certain floating-point operations trigger exceptions. See Intel's processor documentation for details.

This routine allows the programmer to have direct access to the CW. Be aware that using this routine to change the value of the 8087CW will change the behavior of the program's FP calculations. It is the programmer's responsibility to reset it.

It is recommended that you disable all floating-point exceptions when using OpenGL to render 3D graphics. To do this, call Set8087CW(0x133f) in your main form's OnCreate event before calling any OpenGL functions.

C++ Examples:

Copy Code

/*
This example accesses the Floating Point Unit (FPU) control
register.  Try turning floating point exceptions off and on
and dividing a number by zero to test it.
*/
Word Saved8087CW;

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  Edit3->Text = FloatToStr(StrToFloat(Edit1->Text) / StrToFloat(Edit2->Text));
}

void __fastcall TForm1::RadioGroup1Click(TObject *Sender)
{
  if (RadioGroup1->Items->Strings[RadioGroup1->ItemIndex] == "FPU Exceptions")
    System::Set8087CW(Saved8087CW);
  if (RadioGroup1->Items->Strings[RadioGroup1->ItemIndex] == "No FPU Exceptions")
    System::Set8087CW(0x133f); // Disable all fpu exceptions
}

void __fastcall TForm1::FormCreate(TObject *Sender)
{
  RadioGroup1->Items->Add("No FPU Exceptions");
  RadioGroup1->Items->Add("FPU Exceptions");
  RadioGroup1->ItemIndex = 2;
  Saved8087CW = Default8087CW;  // Save this because Set8087CW changes it!
}

void __fastcall TForm1::FormDestroy(TObject *Sender)
{
  System::Set8087CW(Saved8087CW); // Default value (with exceptions) is 0x1372
}

Delphi Examples:

Copy Code

{
This example accesses the Floating Point Unit (FPU) control
register.  Try turning floating point exceptions off and on
and dividing a number by zero to test it.
}
var
  Form1: TForm1;
  Saved8087CW: Word;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
  Edit3.Text := FloatToStr(StrToFloat(Edit1.Text) / StrToFloat(Edit2.Text));
end;

procedure TForm1.RadioGroup1Click(Sender: TObject);
begin
  if RadioGroup1.Items[RadioGroup1.ItemIndex] = 'FPU Exceptions' then
    System.Set8087CW(Saved8087CW);
  if RadioGroup1.Items[RadioGroup1.ItemIndex] = 'No FPU Exceptions' then
    System.Set8087CW($133f); { Disable all fpu exceptions }
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  RadioGroup1.Items.Add('No FPU Exceptions');
  RadioGroup1.Items.Add('FPU Exceptions');
  RadioGroup1.ItemIndex := 2;
  Saved8087CW := Default8087CW;  // Save this because Set8087CW changes it!
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  System.Set8087CW(Saved8087CW); // Default value (with exceptions) is $1372
end;