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| From | Keith Thompson <Keith.S.Thompson+u@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: srand(0) |
| Date | 2026-01-08 14:44 -0800 |
| Organization | None to speak of |
| Message-ID | <87344fhghg.fsf@example.invalid> (permalink) |
| References | <10ib0ka$3cgil$1@dont-email.me> <10icocl$3u4ua$1@dont-email.me> <867bttph43.fsf@linuxsc.com> <87ikddgkc2.fsf@example.invalid> <10joipc$1jc43$1@dont-email.me> |
Michael Sanders <porkchop@invalid.foo> writes:
> On Wed, 07 Jan 2026 13:54:21 -0800, Keith Thompson wrote:
>> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
[...]
>>> Apples and oranges. Many applications that use random numbers
>>> need a stream of numbers that is deterministic and reproducible,
>>> which /dev/urandom is not.
>>
>> And neither is the non-conforming rand() on OpenBSD.
>>
>> The rand(1) man page on OpenBSD 7.8 says:
>>
>> Standards insist that this interface return deterministic
>> results. Unsafe usage is very common, so OpenBSD changed the
>> subsystem to return non-deterministic results by default.
>>
>> To satisfy portable code, srand() may be called to initialize
>> the subsystem. In OpenBSD the seed variable is ignored,
>> and strong random number results will be provided from
>> arc4random(3). In other systems, the seed variable primes a
>> simplistic deterministic algorithm.
>>
>> It does provide an srand_deterministic() function that behaves the way
>> srand() is supposed to.
>
> So then clang would use:
>
> #ifdef __OpenBSD__
> srand_deterministic(seed);
> #else
> srand(seed);
> #endif
>
> But I don't know (yet) that gcc does as well under OpenBSD.
I don't know what you mean when you say that clang "would use"
that code.
I'm not aware that either clang or gcc uses random numbers
internally. I don't know why they would.
You could certainly write the above code and compile it with either
gcc or clang (or any other C compiler on OpenBSD). I've confirmed
that gcc on OpenBSD does predefine the symbol __OpenBSD__. There
should be no relevant difference between gcc and clang; random
number generation is implemented in the library, not in the compiler.
If your point is that a programmer using either gcc or clang could
use the above code to get the required deterministic behavior
for rand(), I agree. (Though it shouldn't be necessary; IMHO the
OpenBSD folks made a very bad decision.)
Relatedly, the NetBSD implementation of rand() is conforming, but
of very low quality. The low-order bit alternates between 0 and
1 on successive rand() calls, the two low-order bits repeat with
a cycle of 4, and so on. Larry Jones wrote about it here in 2010:
The even/odd problem was caused at Berkeley by a well meaning
but clueless individual who increased the range of the generator
(which originally matched the sample implementation) by returning
the *entire* internal state rather than just the high-order
bits of it. BSD was very popular, so that defective generator
got around a lot, unfortunately.
And I've just discovered that the OpenBSD rand() returns alternating
odd and even results after a call to srand_determinstic().
It's disturbing that this has never been fixed.
--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */
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srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-22 08:48 +0000
Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-12-22 06:44 -0500
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-22 13:18 +0100
Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-12-22 12:13 -0500
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-22 18:41 +0100
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-22 20:45 +0200
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-22 21:16 +0000
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-22 22:19 +0100
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-22 22:57 +0100
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-23 11:18 +0200
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-23 10:54 +0100
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-23 13:50 +0200
Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-12-23 18:29 -0500
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-23 16:30 -0800
Re: srand(0) antispam@fricas.org (Waldek Hebisch) - 2025-12-23 17:54 +0000
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-24 00:08 +0200
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-24 02:02 +0000
Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-12-23 23:43 -0500
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-24 05:34 +0000
Re: srand(0) antispam@fricas.org (Waldek Hebisch) - 2025-12-24 09:00 +0000
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-24 12:12 +0200
Article of Melissa O'Nail (Was: srand(0)) Michael S <already5chosen@yahoo.com> - 2025-12-28 02:44 +0200
Re: Article of Melissa O'Nail antispam@fricas.org (Waldek Hebisch) - 2025-12-28 05:38 +0000
Re: Article of Melissa O'Nail Michael S <already5chosen@yahoo.com> - 2025-12-28 12:35 +0200
Re: Article of Melissa O'Nail Michael S <already5chosen@yahoo.com> - 2026-01-05 14:21 +0200
Re: Article of Melissa O'Nail antispam@fricas.org (Waldek Hebisch) - 2026-01-07 10:51 +0000
Re: Article of Melissa O'Nail Michael S <already5chosen@yahoo.com> - 2026-01-08 14:03 +0200
Re: Article of Melissa O'Nail Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-08 09:40 -0800
Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-08 09:26 -0800
Re: srand(0) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-12-24 13:48 -0800
Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-07 08:41 -0800
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-08 01:06 +0200
Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-02-03 05:26 -0800
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-02-03 16:37 +0200
Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-02-17 23:47 -0800
Re: srand(0) Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-02-18 11:21 +0000
Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-19 10:01 +0100
Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-02-19 14:33 -0500
Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-19 20:47 +0100
Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-02-20 16:01 -0500
Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-21 11:09 +0100
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-02-19 14:39 -0800
Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-20 09:16 +0100
Re: srand(0) Paul <nospam@needed.invalid> - 2026-02-23 08:32 -0500
Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-23 16:05 +0100
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-02-23 19:59 +0200
Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-23 20:06 +0100
Re: srand(0) Paul <nospam@needed.invalid> - 2026-02-23 15:24 -0500
Re: srand(0) Axel Reichert <mail@axel-reichert.de> - 2026-02-24 07:08 +0100
Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-24 10:24 +0100
Re: srand(0) Axel Reichert <mail@axel-reichert.de> - 2026-02-26 19:13 +0100
Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-24 05:22 -0600
Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-24 23:09 -0600
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-25 09:51 +0100
Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-25 04:24 -0600
Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-07 07:50 -0800
Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-07 07:46 -0800
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-07 18:14 +0200
Re: srand(0) Kaz Kylheku <046-301-5902@kylheku.com> - 2025-12-22 19:16 +0000
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-22 22:35 +0100
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 07:24 +0000
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-23 09:59 +0100
Re: srand(0) Michael Bäuerle <michael.baeuerle@stz-e.de> - 2025-12-23 11:09 +0100
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 14:49 +0000
Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2025-12-23 16:13 +0000
Re: srand(0) richard@cogsci.ed.ac.uk (Richard Tobin) - 2025-12-23 19:05 +0000
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-23 02:16 -0800
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 14:47 +0000
Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2025-12-23 16:08 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 15:44 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 07:17 +0000
Re: srand(0) David Brown <david.brown@hesbynett.no> - 2025-12-23 08:25 +0100
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 14:45 +0000
Re: srand(0) David Brown <david.brown@hesbynett.no> - 2025-12-23 19:15 +0100
Re: srand(0) John McCue <jmclnx@gmail.com.invalid> - 2025-12-23 00:39 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-23 02:17 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 14:55 +0000
Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-24 23:35 -0600
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-26 08:23 +0000
Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-26 14:48 -0600
Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-26 15:12 -0600
Re: srand(0) Ike Naar <ike@sdf.org> - 2025-12-23 06:49 +0000
Re: srand(0) John McCue <jmclnx@gmail.com.invalid> - 2025-12-23 20:37 +0000
Re: srand(0) Ike Naar <ike@sdf.org> - 2025-12-24 15:22 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 07:25 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-24 06:16 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 15:21 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-24 19:00 +0000
Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-25 03:07 -0600
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-25 19:31 +0000
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-25 21:14 +0100
Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-25 15:29 -0600
Re: srand(0) Paul <nospam@needed.invalid> - 2025-12-25 23:25 -0500
Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-25 23:41 -0600
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-26 05:42 +0000
Re: srand(0) Paul <nospam@needed.invalid> - 2025-12-26 01:52 -0500
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-26 07:56 +0000
Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-26 04:48 -0600
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-24 10:51 +0200
Re: srand(0) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-12-24 00:59 -0800
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 15:28 +0000
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-24 17:44 +0200
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 16:17 +0000
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-24 17:53 +0100
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 17:27 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 17:33 +0000
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-24 20:16 +0200
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-25 02:01 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-25 03:17 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-26 08:13 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-25 04:30 +0000
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-25 09:10 +0100
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-26 08:08 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-30 06:07 +0000
Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2025-12-30 18:42 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-31 02:01 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-31 03:10 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-31 03:28 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-31 09:37 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-01 07:32 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-01 19:02 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-01 19:20 +0000
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-01 21:53 +0200
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-01 23:50 +0000
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-02 14:32 +0200
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-02 16:18 +0200
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-02 20:52 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-02 20:46 +0000
Re: srand(0) Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2026-01-03 04:08 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-03 04:39 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-03 14:24 +0000
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-03 20:38 +0200
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-30 19:37 -0800
Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2025-12-31 17:24 +0000
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 15:17 -0800
Re: srand(0) Paul <nospam@needed.invalid> - 2025-12-31 12:30 -0500
Re: srand(0) bart <bc@freeuk.com> - 2025-12-31 18:42 +0000
Re: srand(0) Paul <nospam@needed.invalid> - 2025-12-31 15:07 -0500
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-31 22:18 +0200
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-31 20:55 +0000
Re: srand(0) bart <bc@freeuk.com> - 2025-12-31 22:57 +0000
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 16:00 -0800
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-01 01:03 +0000
Re: srand(0) bart <bc@freeuk.com> - 2026-01-01 14:05 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-01 19:03 +0000
Re: srand(0) bart <bc@freeuk.com> - 2026-01-01 20:28 +0000
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 15:29 -0800
Re: srand(0) highcrew <high.crew3868@fastmail.com> - 2026-01-01 00:31 +0100
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 16:05 -0800
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-31 15:29 +0200
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-31 20:52 +0000
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 15:14 -0800
Re: srand(0) Geoff <geoff@invalid.invalid> - 2026-01-05 20:00 -0800
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 15:03 -0800
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-30 19:35 -0800
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-31 04:51 +0000
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-31 15:15 +0200
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-31 20:51 +0000
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 15:00 -0800
Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-01 01:45 +0200
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 16:34 -0800
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-01 07:23 +0000
Re: srand(0) Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2026-01-01 02:01 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-01 02:29 +0000
Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-30 06:34 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-30 14:05 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-28 05:51 +0000
Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2025-12-24 17:08 +0000
Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-07 07:39 -0800
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-07 13:54 -0800
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-08 15:34 +0000
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-08 14:44 -0800
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-09 06:06 +0000
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-08 22:46 -0800
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-09 22:38 +0000
Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2026-01-09 23:27 +0000
Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-09 17:09 -0800
Re: srand(0) Kaz Kylheku <046-301-5902@kylheku.com> - 2026-01-10 19:44 +0000
Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-09 00:36 -0800
Re: srand(0) Bonita Montero <Bonita.Montero@gmail.com> - 2025-12-23 11:04 +0100
Re: srand(0) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-12-23 21:44 -0800
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 15:41 +0000
Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-24 18:04 +0100
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-25 05:41 +0000
Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-08 02:57 +0000
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