Date: Mon, 26 Feb 2001 20:27:01 -0800 From: Kris Kennaway <kris@FreeBSD.org> To: Terry Lambert <tlambert@primenet.com> Cc: "Jacques A. Vidrine" <n@nectar.com>, Kris Kennaway <kris@FreeBSD.ORG>, arch@FreeBSD.ORG Subject: Re: rand(3) (was Re: cvs commit: ports/astro/xglobe/files patch-random) Message-ID: <20010226202701.A13175@hub.freebsd.org> In-Reply-To: <200102270400.VAA11366@usr05.primenet.com>; from tlambert@primenet.com on Tue, Feb 27, 2001 at 04:00:22AM %2B0000 References: <20010226211804.A44846@spawn.nectar.com> <200102270400.VAA11366@usr05.primenet.com>
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On Tue, Feb 27, 2001 at 04:00:22AM +0000, Terry Lambert wrote:
> > > > Why do you expect this anyway?
> > >
> > > I am a scientist. Repeatability of experiments is important.
> >
> > I meant: Why do you expect that, for example, Solaris's rand()
> > implementation would give the same results as FreeBSD's rand()
> > implementation, or that on any other platform? The algorithm
> > is not specified by ISO C, nor by POSIX, nor by SUSv2.
>
> [ ... ]
>
> > The implication being, of course, that if you want your results to be the same
> > across platforms, than you need to provide your own PRNG instead of using
> > rand().
>
> The 48 bit linear congruential algorithm is a defacto standard for
> the implementation across UNIX platforms. While the standards do
> not specify this algorithm, in practice it is there, just as, in
> practice, select() does not modify the contents of timeval, even
> though the man page permits it to do so, since code would break.
Don't know where you're pulling 48-bits from (though I have my suspicions :-)
but it's not rand() you're talking about (rand is a 32 bit LCRNG).
> Can someone put forth a use for rand() which requires this change
> to permit the use to employe rand() instead of its own code?
Parse error.
Kris
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