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

[Florian Klaempfl]

Am 07.12.2011 16:03, schrieb Graeme Geldenhuys:
> On 7 December 2011 14:54, Jonas Maebe <jonas.maebe at ....> wrote:
>>
>> That's correct. We use the mersenne twister, Delphi probably a linear
>> congruential generator. The mersenne twister has a much larger period.
> 
> I was reading a bit more about this.  The Mersenne Twister (MT)
> generator has a massive period of 2^19937−1, compared to the XorShift
> generator, which in turn has a period of 2^128-1.
> 
> Most text I read mentions that MT is great for statistical purposes,
> and performs well in its class.
>
> So wouldn't it maybe make more sense to let the standard (read more
> common) Random() call use a higher performance random number
> generator, with a much lower period.

Well, once we thought we try to do things better than Delphi ;) Some
people, I think John Lee, asked for a better random in FPC years ago so
Jonas implemented a MT.

> Then add the MT generator as a
> call to the Maths unit - where more statistical functions are located?
>
> Most applications are not statistical apps, they just want a random
> number here or there, so such high period low performance generator is
> normally not required. Having it in the Maths unit still makes in
> available when needed though - for those specialised apps.
>
> Just a thought...
>

FPC uses MT at least for 10 years and nobody complained about
performance yet. So I suspect the cases might be very rare when random
performance matters and having good random numbers is always a good
thing ... I prefer not to change it but it's fine for me for delphi
compatibility's sake ;)