Warp wrote:
>   The RNG I'm considering supports very large seeds (up to something li
ke
> 8192-bit seeds if so configured) and has very high quality and speed.
> 
	As a simple matter of curiosity, which RNG are you considering?

		Jerome
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Among other things, Warp saw fit to write:

> 3) Use an alternative function for long seeds. For example:
> 
>      #declare S = longseed(2, 1, 2, 3, 4);
> 
> [...]
> 
> 4) Create an entirely new syntax for specifying a group of values. This,
>    however, would be laborious and should preferably be avoided.

Somewhere between 3 and 4:

3.5) Create a sort of "concatenate numbers" function, that would allow
really large numbers, maybe with and arbitrary number of parameters. If the
function is named "numconcat":

seed(1234)   // current
seed(1234,1) // same as above
seed(1234,2) // new RNG with small seed
seed(numconcat(1234,5678,90),2) // new RNG with large seed

The function numconcat need not be a "real" concatenation, i.e., there's no
reason why numconcat(1234,5678,90)=1234567890, it should just create a
large number out of smaller ones.

Hmm... maybe that's what option 4 meant from the beginning, though.

-- 
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

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Tim Attwood <tim### [at] anti-spamcomcastnet> wrote:
> PRNG_Id = seed(Float | Float_Id [, Float | Float_Id [, Array | Array_Id]])

  Btw, just use "float expression" to indicate anything that evaluates to
float in a comprehensive way.

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                                                          - Warp

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> [-- text/plain, encoding quoted-printable, charset: UTF-8, 14 lines --]

> Warp wrote:
> >   The RNG I'm considering supports very large seeds (up to something like
> > 8192-bit seeds if so configured) and has very high quality and speed.
> > 
>         As a simple matter of curiosity, which RNG are you considering?

  The ISAAC RNG, of which I have some experience and have found to be of
very decent quality (should be rather cryptographically strong) and very
fast, and with a very large period. Also according to my experience it's
faster than Mersenne Twister without the need for special compiler options
(the MT can be made as fast, but only if you create a special SSE version
of it).

  (Of course speed is not really crucial here, but the quality should be
very good.)

-- 
                                                          - Warp

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Christian Froeschlin <chr### [at] chrfrde> wrote:
> #declare R = prng {type 1 seed 42}

  I'm not sure if with the POV-Ray parser that 'seed' keyword would cause
a clash with the seed() function. Some names can be used in different
contexts, but I'm not sure this is one of those cases.

-- 
                                                          - Warp

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Warp <war### [at] tagpovrayorg> wrote:
>   (Of course speed is not really crucial here, but the quality should be
> very good.)

Given that there might be some good use for a more sophisticated RNG inside
POV-Ray's rendering engine possibly heading our way (thinking of SSLT here, or
maybe addition of some montecarlo elements), I guess speed *should* be
considered an issue.

So to hear that the RNG you have in mind *is* fairly fast, that's good news.

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What about this algorithm

Xn+1 = SXn - INT(SXn)

See

http://www.number.com.pt/index.html


Phoenix

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Warp wrote:
> "J�r�me M. Berger" <jeb### [at] freefr> wrote:
>> [-- text/plain, encoding quoted-printable, charset: UTF-8, 14 lines --]
> 
>> Warp wrote:
>>>   The RNG I'm considering supports very large seeds (up to something like
>>> 8192-bit seeds if so configured) and has very high quality and speed.
>>>
>>         As a simple matter of curiosity, which RNG are you considering?
> 
>   The ISAAC RNG, of which I have some experience and have found to be of
> very decent quality (should be rather cryptographically strong) and very
> fast, and with a very large period. Also according to my experience it's
> faster than Mersenne Twister without the need for special compiler options
> (the MT can be made as fast, but only if you create a special SSE version
> of it).
> 
>   (Of course speed is not really crucial here, but the quality should be
> very good.)
> 
	Thanks, that's very interesting to know.

		Jerome

PS: If anybody wants more information on ISAAC, Google gave me this 
page: http://burtleburtle.net/bob/rand/isaacafa.html
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> PS: If anybody wants more information on ISAAC, Google gave me this 
> page: http://burtleburtle.net/bob/rand/isaacafa.html

  My C++ version should be much easier to use, though:

http://warp.povusers.org/IsaacRand.zip

-- 
                                                          - Warp

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Phoenex wrote:
> 
> What about this algorithm
> 
> Xn+1 = SXn - INT(SXn)
> 
> See
> 
> http://www.number.com.pt/index.html
> 
	That's a basic LCG (same as the current POV algorithm) except that 
it's implemented in floating point. It will have the same 
shortcomings...

		Jerome
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