[fpc-devel] Growing a memory stream

[Vincent Snijders]

Hi,

Currently the TMemoryStream grows in steps of 4096 bytes.

When writing 100000 chunks of say 80 bytes to it, this causes a lot of 
reallocations. I think it is better to grow at least a quarter for example.

The new code could look something like:
function TMemoryStream.Realloc(var NewCapacity: Longint): Pointer;

begin
   // round off to block size.
   If NewCapacity<0 Then
     NewCapacity:=0
   else begin
     if NewCapacity - Capacity < Capacity div 4 then
	NewCapacity := Capacity + Capacity div 4;
     NewCapacity := (NewCapacity + (TMSGrow-1)) and not (TMSGROW-1);
   end;
   // Only now check !
   If NewCapacity=FCapacity then
     Result:=FMemory
   else
     begin
       Result:=Reallocmem(FMemory,Newcapacity);
       If (Result=Nil) and (Newcapacity>0) then
         Raise EStreamError.Create(SMemoryStreamError);
     end;
end;

What do you think?

For background see:
http://www.freepascal.org/mantis/view.php?id=7270

Vincent