From owner-freebsd-hackers  Tue Feb 18 16: 9: 1 2003
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Date: Tue, 18 Feb 2003 16:04:57 -0800 (PST)
From: Paul Herman <pherman@frenchfries.net>
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To: FreeBSD Hackers <hackers@freebsd.org>
Subject: arc4random() range
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X-Loop: FreeBSD.ORG

Hi,

...a potential quick commit for someone. :-)

What's the concesus that arc4random() should be a drop-in
replacement for rand()/random()?  Consider the following that
caclulates the average of a bunch of random numbers on [0.0, 1.0]:

  bash$ cat rand.c
  #include <stdlib.h>

  int i;
  double avg;

  #define ITERATIONS 1000000
  #define FIND_AVG(func)  do { \
                for (i=0, avg = 0.0; i<ITERATIONS; i++)                 \
                        avg += (double)func()/(double)RAND_MAX;         \
                printf("avg:\t%f\n", avg/ITERATIONS);                   \
                } while (0)

  int main() {
        FIND_AVG(rand);
        FIND_AVG(random);
        FIND_AVG(arc4random);
        return 0;
  }
  bash$ cc rand.c && ./a.out
  avg:    0.500404
  avg:    0.500007
  avg:    1.001370	<--- !!!!!!
  bash$ uname -r
  4.7-STABLE
  bash$

Is is just understood that arc4random() doesn't obey RAND_MAX, or
should it?  Whatever the answer is, perhaps the manpage should
state what the range is like the manpages for rand(3) and random(3)
do.

-Paul.


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