On 12/28/22 22:03, Alejandro Colomar wrote:
> Hi Jonny,
> 
> On 12/28/22 21:56, Alejandro Colomar wrote:
>> Hi Jonny,
>>
>> On 12/28/22 21:51, Jonny Grant wrote:
>>> You're completely right. It's a real issue if software starts multiple times 
>>> per second, or executes in less than one second and then runs again. Our 
>>> software always runs for at least minutes, maybe another code suggestion for 
>>> a seed would be good instead, like arc4random. I do like that rand() offers a 
>>> reproducible sequence, useful when in some other software we logged the seed 
>>> value used. random.4 - /dev/random would be a better seed than time(NULL) if 
>>> running the program multiple times per second. Anyway, rand() is only 
>>> pseudo-random, utilising /dev/random would be really much more random, and I 
>>> like that the seed is saved between reboots.
>>
>> Ahh, I didn't connect the dots the other day!  We don't need to wait for 
>> glibc. libbsd already provides arc4random on GNU/Linux systems, so I can 
>> already recommend using arc4random to seed srand(3).
>>
>> I'll prepare a patch...
>>
> 
> I will probably apply the following patch.  Do you have any comments?  Does it 
> provide the information you wanted to add?
> 
> Cheers,
> 
> Alex
> 
> diff --git a/man3/rand.3 b/man3/rand.3
> index 572471749..350a875d8 100644
> --- a/man3/rand.3
> +++ b/man3/rand.3
> @@ -190,6 +190,9 @@ .SH EXAMPLES
>   pseudo-random sequence produced by
>   .BR rand ()
>   when given a particular seed.
> +When the seed is
> +.IR \-1 ,
> +the program uses a random seed.
>   .PP
>   .in +4n
>   .\" SRC BEGIN (rand.c)
> @@ -211,7 +214,11 @@ .SH EXAMPLES
>       seed = atoi(argv[1]);
>       nloops = atoi(argv[2]);
> 
> -    srand(seed);
> +    if (seed == -1)
> +        srand(src4random());

Oops, typo there

> +    else
> +        srand(seed);
> +
>       for (unsigned int j = 0; j < nloops; j++) {
>           r =  rand();
>           printf("%d\en", r);
> @@ -223,5 +230,6 @@ .SH EXAMPLES
>   .\" SRC END
>   .in
>   .SH SEE ALSO
> +.BR arc4random (3bsd),
>   .BR drand48 (3),
>   .BR random (3)
> 
> 
> 

-- 
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