function Int64ToHex(Value: Int64; Digits: Integer): string;
const
  HexDigitChr: array[0..15] of Char = ( '0','1','2','3','4','5','6','7',
                                        '8','9','A','B','C','D','E','F' );
var
  Buf: array[0..16]  of Char;
  Dest : PChar;
begin
  Dest := @Buf[16];
  Dest^ := #0;
  repeat
    Dec(Dest);
    Dest^ := '0';
    if Value <> 0 then
    begin
      Dest^ := HexDigitChr[Value and $F];
      Value := Value shr 4;
    end;
    Dec(Digits);
  until (Value = 0) and (Digits <= 0);
  Result := Dest;
end;