[squeak-dev] The Trunk: Kernel-bf.899.mcz
Levente Uzonyi
leves at elte.hu
Sun Feb 15 21:02:18 UTC 2015
Thanks for the pointer. It indeed has an implementation of MT, but it's
not very efficient (I suspect that it was written by a student, who was
new to Smalltalk, or Squeak), and it also has a few bugs. I decided to
roll my own version, which can be found in the Inbox as Kernel-ul.903.
Levente
On Fri, 13 Feb 2015, Nicolas Cellier wrote:
> Also look into Sci-Smalltalk, there are several PRNG there.
> For large integers, we need to construct them by chunk anyway.
>
> We construct a large X in interval [0,2^N-1], where for example N is a multiple of 32 for simple PRNG.
> Then we perform Max * X // (2^N) for generating in interval [0,Max-1].
> Some guard must be taken with N > highbit(Max) so as to obtain a fair distribution (uniform).
>
>
> 2015-02-12 20:46 GMT+01:00 Levente Uzonyi <leves at elte.hu>:
> It seems like it only has csprngs. I see there one based on the Fortuna algorithm, and one based on SHA1 in counter mode.
>
> Levente
>
> On Thu, 12 Feb 2015, Levente Uzonyi wrote:
>
> IIRC it has a mersenne twister (which is a quite common choice for prngs). We should check the implementation and see if it's efficient enough.
>
> Levente
>
> On Thu, 12 Feb 2015, Chris Muller wrote:
>
> Maybe adopt one of the ones from the Cryptography package?
>
> On Thu, Feb 12, 2015 at 12:52 PM, Levente Uzonyi <leves at elte.hu> wrote:
> On Tue, 10 Feb 2015, Bert Freudenberg wrote:
>
> On 10.02.2015, at 15:37, commits at source.squeak.org wrote:
>
>
> Bert Freudenberg uploaded a new version of Kernel to project The Trunk:
> http://source.squeak.org/trunk/Kernel-bf.899.mcz
>
> ==================== Summary ====================
>
> Name: Kernel-bf.899
> Author: bf
> Time: 10 February 2015, 4:37:05.988 pm
> UUID: 1cc7d0c6-0a3d-457f-9609-fa508d11310e
> Ancestors: Kernel-eem.898
>
> Fix random for Really Large Integers.
>
> =============== Diff against Kernel-eem.898 ===============
>
> Item was changed:
> ----- Method: Random>>nextInt: (in category 'accessing') -----
> nextInt: anInteger
> " Answer a random integer in the interval [1, anInteger].
> anInteger should be less than 16r80000000. "
>
> anInteger strictlyPositive ifFalse: [ self error: 'Range must be
> positive' ].
> + "avoid Float arithmetic in #next to work with LargeInts"
> + ^ ((seed := self nextValue) asInteger * anInteger // M asInteger)
> + 1!
> - ^ (self next * anInteger) truncated + 1!
>
>
>
>
> We might want to do something better if anInteger > 16r80000000, because
> that's the maximum number of different random integers we can produce. We
> would need to call nextValue twice (or more times) to produce enough
> randomness.
>
>
>
> Fetching more bits from the generator won't be better. This generator has 31
> bits internal state, so it can't generate longer random numbers.
> We need a better PRNG.
>
> Levente
>
>
>
> My fix just solves the immediate problem of running into infinite Floats.
>
> - Bert -
>
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