Date: Wed, 17 Feb 1999 10:08:41 -0500 (EST) From: "Crist J. Clark" <cjc@cc942873-a.ewndsr1.nj.home.com> To: jgrosch@mooseriver.com Cc: patseal@hyperhost.net, freebsd-questions@FreeBSD.ORG Subject: Re: Random Numbers Message-ID: <199902171508.KAA04420@cc942873-a.ewndsr1.nj.home.com> In-Reply-To: <19990216220931.B5145@mooseriver.com> from Josef Grosch at "Feb 16, 99 10:09:31 pm"
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Josef Grosch wrote,
> On Tue, Feb 16, 1999 at 09:36:40PM -0500, Patrick Seal wrote:
> You should seed the random number generator first. Try the following;
And it is my understanding you are best off only seeding it once. My
minor changes to the code are not led by a '>.'
> int randn()
> {
> int rc = 0;
> long value = 0L;
static unsigned long seed = 0L;
>
if ( ! seed ) {
> pid_t pid = getpid();
> time_t now = 0;
>
>
> struct timeval tp;
> struct timezone tzp;
>
> gettimeofday(&tp, &tzp);
> now = tp.tv_sec; /* unnecessary but nice during debugging */
> seed = (unsigned long)(now / pid);
> srandom(seed);
}
> value = random();
>
> rc = (value % 10);
>
> return (rc);
> }
There is a _tiny_ chance the seed might be exactly '0' after the
first pass, in which case the seed will be recalculated next
use. However, this reduces to the previous algorithm which redid the
seed each time.
Also, if you want to make the code work like the original poster,
where the range of the random number is specified, change the
declaration of the function to take an arg,
int randn(int range)
And then instead of the last three lines,
return (random() % range);
The return value is 0 to (range - 1).
--
Crist J. Clark cjclark@home.com
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