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GEBor · Guest

Strings on stack would be much faster than on heap.
Sometimes you would like to use stack strings, like
in the following case:

if ts.IndexOf('vv$'+s) <> -1 then...

Here it weould be much faster if s - an ordinary string -
could be added to a string allocated on the stack, then
this stack variable could be passed to indexof.

A proof of concept implementation is the following:

const
MaxLen=248;

type
SimString=record
refcnt: Integer;
actlen: Integer;
body: array[1..Maxlen] of char;
end;

TMyStringList=class(TStringList)
public
function IndexOf(var s: SimString): integer; overload;
end;

implementation

function TMyStringList.IndexOf(var s: SimString): integer;
asm
add edx,8 // points to record.body
mov ecx,[eax] // self
jmp dword ptr [ecx+$54] // self.indexof
end;

var
t: TMyStringList;

procedure test4;
var s: SimString;
begin
s.refcnt:=-1;
s.actlen:=5;
s.body[1]:='a';
s.body[2]:='l';
s.body[3]:='m';
s.body[4]:='a';
s.body[5]:=#0;
if t.IndexOf(s) = -1 then
//ShowMessage('Not found')
else
//ShowMessage('Found');
end;

initialization
t:=TMyStringList.Create;
t.Text:='alma'#10'barack'#10'dió';

finalization
t.free;

It is approx. 3 times faster than to create an ordinary
string, and using it to search within the string list:

procedure test3;
var s1: string;
begin
s1:='alma';
if t.IndexOf(s1) = -1 then
//ShowMessage('Not found')
else
//ShowMessage('Found');
end;

Maybe I rediscovered the wheel, but it would be
nice if Borland would support this kind of functionality,
with a "StackString" type.

What do you think?

Aleksandr · Guest

Hi.
Source below is not for use. Just a joke.

//NOT WELL TESTED
unit ShaLimitedStrings;

interface

function GetMaxLength(var s: string): integer;
procedure SetMaxLength(var s: string; maxlen: integer);
procedure SetLimitedString(var s: string; buffer: pchar; len: integer);
overload;
procedure SetLimitedString(var s: string; const value: string); overload;

implementation

//GetMaxLength returns MaxInt for ANSI strings, 0 for constants and
//maximal length for our Limited strings
function GetMaxLength(const s: string): integer;
begin;
Result:=integer(s);
if Result<>0 then Result:=pInteger(Result- Cool

^;
if Result>=0 then Result:=MaxInt else Result:= -1-Result;
end;

//Use SetMaxLength to convert ANSI string to Limited one
//and to set it's maximal length or to deallocate Limited string
procedure SetMaxLength(var s: string; maxlen: integer);
var
len: integer;
begin;
if pointer(s)<>nil
then if pInteger(integer(s)- Cool

^<-1
then pInteger(integer(s)- Cool

^:=1; //Set refct to 1
if maxlen=0 then s:='' //Deallocate string
else begin; //Limited string
len:=Length(s);
SetLength(s, maxlen);
pInteger(integer(s)- Cool

^:= -1-maxlen;
if len<maxlen then begin;
pInteger(integer(s)-4)^:=len;
pchar(pointer(s))[len]:=#0;
end;
end;
end;

//SetLimitedString sets value of Limited string
procedure SetLimitedString(var s: string; buffer: pchar; len: integer);
overload;
var
maxlen: integer;
begin;
maxlen:=integer(s);
if maxlen<>0 then maxlen:=pInteger(maxlen- Cool

^; //Get refct
if maxlen>=0 then SetString(s,buffer,len) //ANSI string
else begin; //Limited string
maxlen:= -1-maxlen;
if len>maxlen then len:=maxlen;
System.Move(pointer(buffer)^,pointer(s)^,len);
pInteger(integer(s)-4)^:=len;
pchar(pointer(s))[len]:=#0;
end;
end;

//SetLimitedString sets value of Limited string
procedure SetLimitedString(var s: string; const value: string); overload;
begin;
SetLimitedString(s,pointer(value),length(value));
end;

end.

////////

//This works on my D6
procedure TForm1.Button1Click(Sender: TObject);
var
sl: TStringList;
s, t: string;
begin;
sl:=TStringList.Create;
sl.Text:='alma'#10'barack';

SetMaxLength(s,248); //allocate s
SetLimitedString(s,'alma'); //set value
ShowMessage(IntToStr(sl.IndexOf(s)));
SetLimitedString(s,'barack');
ShowMessage(IntToStr(sl.IndexOf(s)));
SetLimitedString(s,'abc');
ShowMessage(IntToStr(sl.IndexOf(s)));
SetMaxLength(s,0); //deallocate s

sl.Free;
end;

--
regards,
Aleksandr