freepascal.compiler/rtl/objpas/sysutils/syssr.inc

var
  Srch,OldP,RemS: SRString; // Srch and Oldp can contain uppercase versions of S,OldPattern
  P : Integer;
begin
  Srch:=S;
  OldP:=OldPattern;
  if rfIgnoreCase in Flags then
    begin
    Srch:=SRUpperCase(Srch);
    OldP:=SRUpperCase(OldP);
    end;
  RemS:=S;
  Result:='';
  while (Length(Srch)<>0) do
    begin
    P:=AnsiPos(OldP, Srch);
    if P=0 then
      begin
      Result:=Result+RemS;
      Srch:='';
      end
    else
      begin
      Result:=Result+Copy(RemS,1,P-1)+NewPattern;
      P:=P+Length(OldP);
      RemS:=Copy(RemS,P,Length(RemS)-P+1);
      if not (rfReplaceAll in Flags) then
        begin
        Result:=Result+RemS;
        Srch:='';
        end
      else
         Srch:=Copy(Srch,P,Length(Srch)-P+1);
      end;
    end;
end;