[LC++]Random numbers
Yosi
natask at hotmail.com
Sun Sep 2 19:14:46 UTC 2001
Hi,
While on the topic of random numbers, can anyone on the list recommend
a platofrm-independent implementation of a PRNG (pseudo random
generator), preferably in C++, but one in C will just as good. I'm more
interested in having an implementation that works on UNIX/Windows/Novell
and care less if it implemented in C or C++.
Sincerely,
Yosi
>From: Mark Phillips <mark at austrics.com.au>
>Reply-To: tuxcpprogramming at lists.linux.org.au
>To: Linux C++ Programming List <tuxcpprogramming at lists.linux.org.au>
>Subject: [LC++]Random numbers
>Date: Fri, 31 Aug 2001 17:23:26 +0930
>
>Hi,
>
>Doing "man 3 rand" on a linux system gives the following information
>about random number generation:
>
> The versions of rand() and srand() in the Linux C Library
> use the same random number generator as random() and
> srandom(), so the lower-order bits should be as random as
> the higher-order bits. However, on older rand()
> implementations, the lower-order bits are much less random
> than the higher-order bits.
>
> In Numerical Recipes in C: The Art of Scientific Computing
> (William H. Press, Brian P. Flannery, Saul A. Teukolsky,
> William T. Vetterling; New York: Cambridge University
> Press, 1992 (2nd ed., p. 277)), the following comments are
> made:
> "If you want to generate a random integer between 1
> and 10, you should always do it by using high-order
> bits, as in
>
> j=1+(int) (10.0*rand()/(RAND_MAX+1.0));
>
> and never by anything resembling
>
> j=1+(rand() % 10);
>
> (which uses lower-order bits)."
>
>Is the comment from Numerical Recipes in C based on older versions
>of rand()? Ie is it that the first method above (of generating
>a number between 1 and 10) used to be preferable to the second
>method, but now with improved random number generators, the
>second method is just as good --- (and quicker!)??
>
>Thanks,
>
>Mark.
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