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List:       kde-devel
Subject:    Random (Was: Cannot run KDE snapshot :()
From:       Waldo Bastian <bastian () suse ! de>
Date:       1999-12-10 9:19:28
[Download RAW message or body]

On Fri, 10 Dec 1999, Stephan Kulow wrote:
> Alex Zepeda wrote:
> > 
> > On Thu, 9 Dec 1999, Stephan Kulow wrote:
> > 
> > > > Do you know of any better way to get a random number?
> > > >
> > > Well, you could as a compromise reset the random seed
> > 
> > How?  Wouldn't you have to have root access to set the clock?
> > 
> What has the clock to do with the random seed? Nothing inspite
> that most people abuse the clock for getting a semi random start
> seed. The problem comes if you use the KTempFile constructor
> more than once in a second, it will init the seed with the same
> number resulting in the same output. 

Hm interesting. That could cause a problem when you need more than 3
tempfiles within a second.

Can't we init the random seed in KApplication and make it a policy not
to touch the random seed? If you need reproducable sequences just write
your own sequence generator. (That's not too difficult, I just need to
dig out my math books.)

We could provide:

int KApplication::random() // Generate a truly unpredictable number.

and 
class KSequence // Generate a random sequence 
{
public:
  KSequence(int seed=0);
  int number();
private:
  ....
}

KSequence(N) initialize the sequence with N for N >0 and with
kapp->random() for N == 0.

Cheers,
Waldo

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