From: nobu.nokada@...
Date: 2003-03-22T10:33:10+09:00
Subject: Re: redefining rand and srand

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Hi,

At Sat, 22 Mar 2003 03:30:00 +0900,
Judson Lester wrote:
> > A couple of questions:
> > 1) how good is Ruby's rand function (what's the quality of randomness)? I
> > suspec that it is just the same as C's rand, so there won't be a
> > difference.
> > 2) I'd like to plug in my own random number generator that would
> > probably
> > produce higher-quality random numbers than the current rand does.  I'm
> > pretty sure it should be doable and easy, like:
> >
> > module Kernel
> >  def rand(max=0)
> >    #do random number generation magic here
> >  end
> > end
> 
> So long as we're redefining rand, and srand, can I recommend that they
> be put into a Random object?  It is occasionally very helpful to have
> separate random number domains.  Especially when you're trying to
> abuse a PRNG.

Tried.

There are Random and Random::MT classes, former is the
interface and stub, and latter is an implementation.  All
methods of MT are internal, and RNG classes must implement the
first 3 methods (initialize, seed, next) and should do the last
(copy_object).

--- Random::seed
    generates appropriate seed integer.

--- Random::default, Random::default=
    accessor for default RNG class.  defaulted to Random::MT.

--- Random::current, Random::current=
    accessor for current RNG instance.  never returns nil.

--- Random#rand([max=nil])
    returns next random value.



--- Random::MT#initialize([seed=nil])
    returns seed value.

--- Random::MT#seed
    returns seed value.

--- Random::MT#next
    returns next random value as Float.

--- Random::MT#copy_object(obj)
    copies the content from obj.



# Calling Random#next as method would make rand() much slower,
# but "fast method call" (mentioned in [ruby-dev:19781] a
# little) might be efficient.


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-- 
Nobu Nakada

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