private void button1_Click(object sender, System.EventArgs e)
{
 int bgnTime = System.Environment.TickCount;
 string Appdata = System.Environment.GetEnvironmentVariable("Appdata");
 string dubleAppdata = "";
 for (int i = 0; i < 1000000; i++)
 {
   dubleAppdata = Appdata.Replace("\\","\\\\");
 }
 int FullTime = System.Environment.TickCount-bgnTime;
 textBox1.Text = dubleAppdata + " "+FullTime.ToString();
}

procedure TForm1.Button3Click(Sender: TObject);
var
 BgnTime,LastTime,TestTime: Integer;
 i: integer;
 S, DubleAppData: String;
begin
 BgnTime:=GetTickCount;
 S:=GetEnvironmentVariable('AppData');
 for i:=1 to 1000000 do begin
   StringReplace(S,'\','\\',[rfReplaceAll]);
 end;
 LastTime := GetTickCount;
 TestTime := LastTime-BgnTime;
 //if TestTime > 1000 then TestTime := TestTime div 1000;
 Memo1.Lines.Add('End test StringReplace: time = '+IntToStr(TestTime)+ ' mc');
end;

function StrReplace(const S, OldPattern, NewPattern: string; Flags: TReplaceFlags): string;
var
 SLen,  NPLen,Index, Count : Integer;
 temp, SearchStr, Patt  : String;
begin
 Count  := 1;
 Index  := 1;
 SLen   := Length(S);
 NPLen  := Length(OldPattern);
 if (S = '') or (OldPattern = '') then Exit;
 Setlength(temp,NPLen);

 if rfIgnoreCase in Flags then
 begin
   SearchStr := AnsiUpperCase(S);
   Patt      := AnsiUpperCase(OldPattern);
 end else
 begin
   SearchStr := S;
   Patt      := OldPattern;
 end;

 While true do begin

   if (Pred(Count)+NPLen) > SLen then begin
     Result:=Result+Copy(SearchStr,Index,(Count+NPLen)-Index);
     Break;
   end;

   Move(SearchStr[Count],temp[1],NPLen);
   if temp = Patt then begin
     Result:=Result+copy(SearchStr,Index,count-Index)+NewPattern;
     inc(count,NPLen);
     Index:=count;
     if Not (rfReplaceAll in Flags) then begin
       Result:=Result+Copy(SearchStr,Index,(Count+NPLen)-Index);
       Break;
     end;
     continue;
   end;
   inc(count);
 end;
end;