Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:80389
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain ajf.me designates 192.64.116.200 as permitted sender)
Content-Type: text/plain; charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 8.1 \(1993\))
In-Reply-To: <54B30DB9.3000003@seld.be>
Date: Mon, 12 Jan 2015 00:05:51 +0000
Cc: PHP Internals List <internals@lists.php.net>
Content-Transfer-Encoding: quoted-printable
Message-ID: <76B8D342-43E7-42E6-AD82-FCF7C5CA8658@ajf.me>
References: <E472413E-7615-49F9-BE6C-AAA0088C3F53@ajf.me> <54B30DB9.3000003@seld.be>
To: Jordi Boggiano <j.boggiano@seld.be>,
 Yasuo Ohgaki <yohgaki@ohgaki.net>
Subject: Re: [PHP-DEV] rand(), mt_rand() and limits
From: ajf@ajf.me (Andrea Faulds)

Hey Yasuo and Jordi,

> On 11 Jan 2015, at 23:56, Jordi Boggiano <j.boggiano@seld.be> wrote:
>=20
> On 11/01/2015 22:12, Andrea Faulds wrote:
>>   * Make mt_srand() and srand() do nothing and produce a deprecation =
notice
>=20
> That is the only point with which I disagree. Looking at =
http://3v4l.org/FLHBV we see that while indeed across PHP versions the =
result has not always been the same, it generally is, and especially =
within one given version setting a seed means you get predictable =
results.
>=20
> This has benefits in some cases like fixtures generation where it =
might not be important if the output changes when you upgrade PHP, but =
you don't want entirely different fixtures every single time. Obviously =
if we could guarantee the algo won't change it would be even better.
>=20
> Bottom line is I think it's important to have the ability to set the =
seed yourself.

>=20
> On 11 Jan 2015, at 23:57, Yasuo Ohgaki <yohgaki@ohgaki.net> wrote:
>=20
> However, I object removal of srand.
> Game programmers need "the same random sequence" on occasion.
> There should be srand to get the same sequence for repeatable =
behaviors.
>=20
> rand()/srand() may be renamed to sys_rand()/sys_srand() (or whatever=20=

> suitable name for them) in case user needs system random sequence=20
> for whatever reasons. I don't insist to keep system's rand/srand, =
though.

I don=E2=80=99t disagree with having some mechanism for predictable =
random number generation from a seed, but I think the global random =
number generator is the wrong place to do it. It=E2=80=99s not =
guaranteed to be predictable, and everything uses it, so some library =
you=E2=80=99re using might advance it without you realising.

Much better would be to add a new, OOP API that gives you your own =
number generator (no global state) and requires explicitly specifying =
the algorithm (cross-version compatibility), with a guarantee that it =
won=E2=80=99t break in new PHP versions.

Something like this, maybe:

    $numgen =3D new RandomNumberGenerator(RAND_MERSENNE_TWISTER, =
time()); // could auto-seed with time()
    $randInt1 =3D $numgen->getInt(0, 100); // gets random integer and =
advances this generator
    list($randInt2, $numgen) =3D $numgen->newGetInt(0, 100); // gets =
random integer and returns a new, advanced generator
    $serialised =3D $numgen->serialiseState(); // Or maybe =
$numgen->getSeed() ?

Does that work?

--
Andrea Faulds
http://ajf.me/