in reply to Re: Re: A little C code converted to Perl *HELP*
in thread A little C code converted to Perl *HELP*

I'd never encountered the apparant 16-bit limitation of perl's built-in rand function.
Hmm... I always thought it was 24 bits. Maybe not for perl?

Anyway, this old TPJ article (from 1996) discusses rand() in a little more depth, including the repeat cycle, for which slavishly following up the example implementation, in ANSI C libraries, is to blame. That was then... things might have changed since then, depending on the agenda of the P5P.

  • Comment on Re: Re: Re: A little C code converted to Perl *HELP*

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Re: Re: Re: Re: A little C code converted to Perl *HELP*
by BrowserUk (Patriarch) on Nov 04, 2003 at 04:55 UTC

    Thanks. The article was very interesting, and produced a very useful piece of information. 

    E:\perl5.8.1\bin>.\perl -MPOSIX=RAND_MAX -e"print RAND_MAX"

32767

    [download]
    So, as of perl 5.8.1, rand is limited to 15-bits! S'funny how long you can go with discovering, reading about or falling foul of these things. Anyway. I have now added 
    use Math::Random::MT qw[ srand rand ];

    [download]

    to my .pl template file.

    This uses The Mersenne Twister PRNG, rather than a Linear Congruential one, and is good for producing the full range of 32-bit unsigned integers.

    Examine what is said, not who speaks.
    "Efficiency is intelligent laziness." -David Dunham
    "Think for yourself!" - Abigail
    Hooray!
    Wanted!

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