Delphi Sytem单元 Set8087CW、Get8087CW、Default8087CW - FPU浮点值运算器

procedure Set8087CW(NewCW: Word);
begin
  Default8087CW := NewCW;
  asm
        FNCLEX  // don‘t raise pending exceptions enabled by the new flags
{$IFDEF PIC}
        MOV     EAX,[EBX].OFFSET Default8087CW
        FLDCW   [EAX]
{$ELSE}
        FLDCW   Default8087CW
{$ENDIF}
  end;
end;

function Get8087CW: Word;
asm
        PUSH    0
        FNSTCW  [ESP].Word
        POP     EAX
end;

Default8087CW: Word = $1332;{ Default 8087 control word.  FPU control register is set to this value.   默认8087控制字。FPU控制寄存器设置为该值。
                                CAUTION:  Setting this to an invalid value could cause unpredictable behavior. 警告：将此值设置为无效值可能会导致不可预知的行为。 }

Set8087CW($1372):     //开FPU,   默认值（例外情况除外）为  $1372 =4978   $137F=4991
Set8087cw($133F):     //闭FPU  ,禁用所有FPU异常   $133F=4927    $1332 =4914  
Get8087CW;  　　 //获取当前的FPU值
Default8087CW;  //获取FPU的默认值，系统运行后，默认是开启，即4978

//滔Roy 2020.12.14
var
  Form1: TForm1;
  Saved8087CW: Word;

implementation

{$R *.dfm}

procedure TForm1.RadioGroup1Click(Sender: TObject);
begin
  if Saved8087CW=0 then Exit;    //防止没设定之前加载 ，否则报错： Invalid floating point operation.
  if RadioGroup1.Items[RadioGroup1.ItemIndex] = ‘No FPU Exceptions‘ then   //禁用后，不会抛出异常   结果：INF
    Set8087CW($133f);   { Disable all fpu exceptions. 禁用所有fpu异常。  $133F=4927  }
  if RadioGroup1.Items[RadioGroup1.ItemIndex] = ‘FPU Exceptions‘ then    //FPU开启后，运算会抛出异常  Floating point division by zero
    Set8087CW(Saved8087CW);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Edit3.Text := FloatToStr(StrToFloat(Edit1.Text) / StrToFloat(Edit2.Text));
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.   保存此项是因为Set8087CW更改了它。
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  Set8087CW(Saved8087CW); // Default value (with exceptions) is $1372.     默认值（例外情况除外）为 $1372
end;