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From: john@frog.UUCP (John Woods)
Newsgroups: comp.lang.c
Subject: Re: Random number generator
Message-ID: <10909@frog.UUCP>
Date: 28 Dec 89 02:41:00 GMT
References: <83943@linus.UUCP> <940001@hpavla.HP.COM>
Organization: Misanthropes-R-Us
Lines: 27

In article <940001@hpavla.HP.COM>, gary@hpavla.HP.COM (Gary Jackoway) writes:
> > I was trying to generate a random number bewteen 0 and maxlongint (i.e. 2^32)
> > on my machine (80386 with Interactive). The rand() function that I have
> > returns a psuedo-random number between 0 and MAXINT (which in this case
> > is 32768). 

I assume you mean 32767.

>        longrand = (unsigned long) rand() | ((unsigned long) rand() << 32);

This is the second wrong answer I've seen.  A correct answer is

	typedef unsigned long ulong;

	longrand = (ulong)rand() | ((ulong)rand() << 15)
				 | (((ulong)rand()&3) << 30);

The first wrong answer shifted by 16, but rand() as described returns a 15-bit
integer.

A better solution (IMHO) is to grab Knuth Vol. 2 and code up a good 32 bit
RNG of your own.
-- 
John Woods, Charles River Data Systems, Framingham MA, (508) 626-1101
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