[fpc-devel] Performance of string handling in trunk

[Michael Schnell]

On 06/25/2013 01:20 PM, Hans-Peter Diettrich wrote:
> Michael Schnell schrieb:
>> Supposedly the length and encoding number and code-bytecount is 
>> copied, too.
>
> Please understand reference counted memory objects :-]
Please check this program I tested with a pre-Unicode Delphi.

It shows that (of course) the string length gets copied when assigning a 
string variable to another and how it is done.

-Michael




===========================================================================0
var
  s1, s2: String;
  i1, i2: Integer;
  j1, j2: Integer;
  l1, l2: Integer;
  p1, p2: PChar;
  x1, x2: PInteger;
  y1, y2: PInteger;
  z1, z2: PInteger;
procedure TForm12.FormCreate(Sender: TObject);
begin

  s1 := 'ABCDEFG';


  l1 := Length(s1);
  l2 := Length(s2);
  p1 := pchar(s1);
  p2 := pchar(s2);
  i1 := Integer(@s1);
  i2 := Integer(@s2);
  j1 := Integer(p1);
  j2 := Integer(p2);
  x1 := PInteger(j1);
  x2 := PInteger(j2);
  y1 := PInteger(j1-4);
  y2 := PInteger(j2-4);
  z1 := PInteger(j1-8);
  z2 := PInteger(j2-8);
  Memo1.Lines.Add('l : ' + IntToStr(l1) + ' ' + IntToStr(l2));
  Memo1.Lines.Add('i : ' + IntToHex(i1,  8) + ' ' + IntToHex(i2,  8) + ' 
(@s)');
  Memo1.Lines.Add('j : ' + IntToHex(j1,  8) + ' ' + IntToHex(j2,  8) + ' 
(s    = String Record)');
  Memo1.Lines.Add('x^: ' + IntToHex(x1^, 8) + ' ' + IntToHex(x2^, 8) + ' 
(^s-0 = Content)');
  Memo1.Lines.Add('y^: ' + IntToHex(y1^, 8) + ' ' + IntToHex(y2^, 8) + ' 
(^s-4 = Length)');
  Memo1.Lines.Add('z^: ' + IntToHex(z1^, 8) + ' ' + IntToHex(z2^, 8) + ' 
(^s-8)= RefCount');

  s2 := s1;
  Memo1.Lines.Add('====================');
  l1 := Length(s1);
  l2 := Length(s2);
  p1 := pchar(s1);
  p2 := pchar(s2);
  i1 := Integer(@s1);
  i2 := Integer(@s2);
  j1 := Integer(p1);
  j2 := Integer(p2);
  x1 := PInteger(j1);
  x2 := PInteger(j2);
  y1 := PInteger(j1-4);
  y2 := PInteger(j2-4);
  z1 := PInteger(j1-8);
  z2 := PInteger(j2-8);
  Memo1.Lines.Add('l : ' + IntToStr(l1) + ' ' + IntToStr(l2));
  Memo1.Lines.Add('i : ' + IntToHex(i1,  8) + ' ' + IntToHex(i2,  8) + ' 
(@s)');
  Memo1.Lines.Add('j : ' + IntToHex(j1,  8) + ' ' + IntToHex(j2,  8) + ' 
(s    = String Record)');
  Memo1.Lines.Add('x^: ' + IntToHex(x1^, 8) + ' ' + IntToHex(x2^, 8) + ' 
(^s-0 = Content)');
  Memo1.Lines.Add('y^: ' + IntToHex(y1^, 8) + ' ' + IntToHex(y2^, 8) + ' 
(^s-4 = Length)');
  Memo1.Lines.Add('z^: ' + IntToHex(z1^, 8) + ' ' + IntToHex(z2^, 8) + ' 
(^s-8)= RefCount');
end;