[fpc-pascal] Why is Random(255) some 529x slower compared to Delphi 7?

[Graeme Geldenhuys]

On 9 December 2011 10:02, Vincent Snijders wrote:
>
> I have one question about this code, why is RandSeed set inside the
> loop and not outside the loop or even at the program start?


For the full code as used by tiOPF, see the following URL.

 http://tiopf.svn.sourceforge.net/viewvc/tiopf/tiOPF2/Trunk/Options/tiEncryptSimple.pas?revision=2143&view=markup

I didn't write this encryption code, I merely debugged why the unit
tests for this unit took so long to complete, compared to under
Delphi.

Looking at the code again, I have no idea how it will affect the
encryption algorithm if I move the assignment to RandSeed outside the
loop (just after the first assignment to ByteValue). As a test, made
your suggested change and ran the unit tests. The unit tests still
pass, and the performance under FPC has drastically improved. FPC
(64-bit) is now roughly 4 times slower that Delphi. Much better
indeed, and an acceptable result.

I'll see if I can get hold of the original author of this code and
what they think about the suggested change - and if it will affect the
encryption algorithm at all.

Thanks Vincent for mentioning this. I totally overlooked that.


-- 
Regards,
  - Graeme -


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