Hi,
I'm busy working on some of the remaining unit tests for the tiOPF
project that doesn't run 100% to my satisfaction yet under FPC
(compared to Delphi 7). One of the tests is for a Simple Encryption
algorithm implemented in tiOPF, that runs extremely slow under FPC
2.4.x (and 2.6.0-rc), and near instant under Delphi 7. I'm trying to
figure out why.
Below is a snippet of code I tracked down which contains the slowdown.
The problem under FPC lies with line 08, and more specifically the
call to Random(255). Simply replacing the Random(255) call with a
variable speeds up the loop by some 529 times!
I did a simple GetTickCount() timing around this loop. Delphi executes
the loop in 20 ticks. FPC 2.6.0-rc2 takes 10585 ticks!!!! The outer
loop runs 200400 iterations. The types for BitValue, ByteValue and
RandSeed is of type Byte.
01 for Index := 1 to Length(Source) do
02 begin
03 OrdValue := Ord(Source[Index]);
04 for BitCount := 0 to 7 do
05 begin
06 BitValue := Byte(OrdValue and (1 shl BitCount) = 1 shl BitCount);
07 RandSeed := ByteValue;
08 ByteValue := (((Random(255) + 1) div 2) * 2) + BitValue;
09 Result[(Index - 1) * 8 + BitCount + 1] := AnsiChar(ByteValue);
10 end;
11 end;
I'm using 64bit Ubuntu Linux 10.04.3 with 64-bit FPC 2.6.0-rc2.
Anybody have any ideas why the code under FPC runs so slowly? Is it
maybe some type conversion problem in FPC? I noticed that Random()
returns a Int64 on my Linux system. I'm not sure what it returns under
Delphi 7 (the docs don't say, and I can see the implementation of it).
If you wanted to test this, I attached a fully working program code
(snippets from the original tiOPF code) to demonstrate the problem.
--
Regards,
- Graeme -
_______________________________________________
fpGUI - a cross-platform Free Pascal GUI toolkit
http://fpgui.sourceforge.net
program speedtest;
{$IFDEF FPC}
{$mode delphi}{$H+}
{$ELSE}
{$APPTYPE Console}
{$ENDIF}
uses
Classes, SysUtils;
function GetTickCount: Cardinal;
begin
Result := Cardinal(Trunc(Now * 24 * 60 * 60 * 1000));
end;
function GetTestString: string;
var
i : integer;
lsLine : string;
begin
SetLength(lsLine, 1000);
for i := 1 to 1000 do
lsLine[ i ]:= Chr(ord('A')+random(ord('z')-ord('A')));
for i := 1 to 200 do
result := result + lsLine + #13 + #10;
result := result + 'x'; // make it an odd number
end;
function EncryptString(const psData : AnsiString): AnsiString;
var
OrdValue: Byte;
Index: Integer;
BitCount: Integer;
BitValue: Byte;
ByteValue: Byte;
Source: ansiString;
c: Cardinal;
begin
writeln('Length(psData) = ', Length(psData));
ByteValue := Random(255) + 1;
writeln('ByteValue: ', ByteValue);
Source := psData;
writeln('Length(Source) = ', Length(Source));
SetLength(Result, Length(Source) * 8);
writeln('First Loop....');
c := GetTickCount;
for Index := 1 to Length(Source) do
begin
OrdValue := Ord(Source[Index]);
for BitCount := 0 to 7 do
begin
BitValue := Byte(OrdValue and (1 shl BitCount) = 1 shl BitCount);
RandSeed := ByteValue;
ByteValue := (((Random(255) + 1) div 2) * 2) + BitValue;
{ Replace the above line with the following to see the speed difference }
// ByteValue := (((ByteValue + 1) div 2) * 2) + BitValue;
Result[(Index - 1) * 8 + BitCount + 1] := AnsiChar(ByteValue);
end;
end;
writeln('elapsed time: ', GetTickCount - c);
end;
var
s: string;
begin
Randomize;
s := GetTestString;
s := EncryptString(s);
end.
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