POV-Ray : Newsgroups : povray.beta-test : POV-Ray v3.8.0-beta 1 - Parse error using "%s" in Win10 : Re: POV-Ray v3.8.0-beta 1 - Parse error using "%s" in Win10 Server Time
21 Jun 2024 01:48:08 EDT (-0400)
  Re: POV-Ray v3.8.0-beta 1 - Parse error using "%s" in Win10  
From: Alain Martel
Date: 27 Jul 2021 10:40:25
Message: <61001ad9$1@news.povray.org>

> Am 26.07.2021 um 10:34 schrieb jr:
>> demo scene TdG mentioned simply needs a (fairly) reliable unique seed 
>> for the

>> and am
>> thinking of using something like the following to replace the
>> 'datetime(now,"%s")', and would appreciate comment(s):
>> #declare seed_ = mod((now-int(now))*1e16,1e9);
> - Variable name should use uppercase as the first letter. Just saying.
> - No need for `mod`, as the seeding via `#declare MyRNG = seed(seed_);` 
> already effectively does a `mod` operation with a modulus of 2^32 (ca. 
> 4e9).
> - Taking the time of day, rather than the running total, is a smart move 
> I probably wouldn't have thought of, and had me thinking thrice to 
> figure out whether it even has any advantage. (My preliminary 
> conclusion: I think it does.)
> - Multiplying with 1e16 seems excessive. The value is given in days, and 
> has a precision of microseconds at best; 8.64e10 would be the ideal 
> factor in that case. Some systems may even provide timers as slow as one 
> tick mer millisecond, in which case there would be little point in using 

> There might be some point in multiplying with a very large number and 
> then applying `mod`, so that seeds quickly diverge. But that doesn't 
> work when the multiplying factor is a multiple of the modulus - you'd 
> ideally want coprime values for that, otherwise you're not shuffling 
> around information, you're just ditching digits.
> This should be easy to accomplish by using any odd (in the literal 
> sense) multiplier, while ditching your own mod and relying on the 
> inbuilt mod 2^32 operation. I have a hunch that numbers with a 
> well-balanced number of binary ones and zeros would be ideal.
> The following might do nicely:

When I want coprimes, I often plug in pi in the mix, or use two values 
that differ by 1. It could be something like :

#declare Seed_ = mod(now*pi*100000000, 87654321);

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