Date: Tue, 18 Feb 2003 20:32:48 -0500 From: Anthony Schneider <anthony@x-anthony.com> To: Paul Herman <pherman@frenchfries.net> Cc: FreeBSD Hackers <hackers@FreeBSD.ORG> Subject: Re: arc4random() range Message-ID: <20030219013247.GA10910@x-anthony.com> In-Reply-To: <20030218153651.A240-100000@mammoth.eat.frenchfries.net> References: <20030218153651.A240-100000@mammoth.eat.frenchfries.net>
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an issue of arc4random return u_int32_t and rand*
returning int (ie unsigned vs signed)?
-Anthony.
On Tue, Feb 18, 2003 at 04:04:57PM -0800, Paul Herman wrote:
> 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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