Question

We have a bit of an issue here. We have upgraded from Delphi 2006 to Delphi XE2 and are in the process of converting our code.

The problem is, we use the value -693594 through our application and database records to represent no date (zero date). In Delphi 2006 the FormatDateTime function would correctly format this as 00/00/0000 (given a date format of dd/mm/yyyy).

However in Delphi XE2 they have added a call to ValidateTimeStampDate in the DateTImeToTimeStamp function in System.SysUtils which raises the error “invalid floating point operation”. passing anything greater than -693594, such as -693593, works fine.

Has anyone else had this issue and/or does anyone know a work around?

Answer 1

If you are really desperate to patch back to the previous behaviour you could use something like this:

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure PatchCode(Address: Pointer; const NewCode; Size: Integer);
var
  OldProtect: DWORD;
begin
  if VirtualProtect(Address, Size, PAGE_EXECUTE_READWRITE, OldProtect) then
  begin
    Move(NewCode, Address^, Size);
    FlushInstructionCache(GetCurrentProcess, Address, Size);
    VirtualProtect(Address, Size, OldProtect, @OldProtect);
  end;
end;

type
  PInstruction = ^TInstruction;
  TInstruction = packed record
    Opcode: Byte;
    Offset: Integer;
  end;

procedure RedirectProcedure(OldAddress, NewAddress: Pointer);
var
  NewCode: TInstruction;
begin
  NewCode.Opcode := $E9;//jump relative
  NewCode.Offset := NativeInt(NewAddress)-NativeInt(OldAddress)-SizeOf(NewCode);
  PatchCode(OldAddress, NewCode, SizeOf(NewCode));
end;

function DateTimeToTimeStamp(DateTime: TDateTime): TTimeStamp;
const
  FMSecsPerDay: Single = MSecsPerDay;
  IMSecsPerDay: Integer = MSecsPerDay;
var
  LTemp, LTemp2: Int64;
begin
  LTemp := Round(DateTime * FMSecsPerDay);
  LTemp2 := (LTemp div IMSecsPerDay);
  Result.Date := DateDelta + LTemp2;
  Result.Time := Abs(LTemp) mod IMSecsPerDay;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowMessage(FormatDateTime('dd/mm/yyyy', -693594));
end;

initialization
  RedirectProcedure(@System.SysUtils.DateTimeToTimeStamp, @DateTimeToTimeStamp);

end.

This will work for 32 bit code. It will also work for 64 bit code provided that both the old and new functions reside in the same executable module. Otherwise the jump distance may exceed the range of a 32 bit integer. It will also not work if your RTL resides in a runtime package. Both of these limitations can be readily remedied.

What this code does is re-route all calls to SysUtils.DateTimeToTimeStamp to the version implemented in this unit. The code in this unit is just the PUREPASCAL version from the XE2 source.

The only other approach that meets the needs outlined in your comments is to modify and re-compile the SysUtils unit itself, but I personally avoid that sort of solution.