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From: volf@oasis.IAEhv.nl (Frank Volf)
Message-Id: <199511191351.OAA04737@oasis.IAEhv.nl>
Subject: What's wrong with this code???
To: freebsd-questions@freebsd.org
Date: Sun, 19 Nov 1995 14:51:37 +0100 (MET)
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Hi,

I have an application that uses random() to generate random numbers. For
generating the random numbers I use the following piece of code:

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>

main()
{
  int i;
  long t;

  t = time(NULL);
  srandom((u_int)t);
  printf("%ld %d %d %d\n",t, random() % 8, random() % 8, random() % 8); 
}

To my surprise the range of numbers generated is not random at all between
multiple invocations of the program. In fact the random generator seems
to start again after 16 invocations (with 1 second delay between them
so t has incremented):

816788556 6 1 1
816788557 5 6 3
816788558 5 3 6
816788559 4 0 0
816788560 4 5 3
816788561 3 2 5
816788563 2 4 2
816788564 2 1 5
816788565 1 6 7
816788566 1 3 2
816788567 0 0 4
816788568 0 5 7
816788569 7 2 1
816788570 7 7 4
816788571 6 4 6

816788572 6 1 1
816788573 5 6 3
816788574 5 3 6
816788575 4 0 0

etc.

What is wrong? Is it a bug in my program (maybe the cast?) or is there a
problem with the random number generator used in FreeBSD?

Regards,

            Frank

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       Frank Volf - Internet Access Eindhoven - Digitale Stad Eindhoven 
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