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Date: Mon, 12 Jan 2015 01:06:46 -0800
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To: Stanislav Malyshev <smalyshev@gmail.com>, Andrea Faulds <ajf@ajf.me>
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Subject: Re: [PHP-DEV] rand(), mt_rand() and limits
From: rasmus@lerdorf.com (Rasmus Lerdorf)

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On 01/11/2015 06:05 PM, Stanislav Malyshev wrote:
> Hi!
>=20
>> Also, FWIW, anyone who used the Suhosin patch couldn=E2=80=99t use sra=
nd()
>> because it disabled it.
>=20
> And? You can disable any function in PHP, that doesn't mean anything.
>=20
>> Because if we don=E2=80=99t break it, people will continue to rely on =
it, and
>> this binds our hands for future versions.
>=20
> Sorry, that doesn't sound even remotely like a good reason. It doesn't
> provide any benefit to the user, but produces problems for those who us=
e
> it. The gain for the users is zero, the added trouble - for those who
> use the feature - is substantial.
>=20
>> Also, those people will have their code break anyway if they upgrade
>> their OS and it changes its random number generator.
>=20
> If they used mt_rand that is not true. And OS RNG changes are not that
> frequent. E.g. the manual for srand on Mac (and, likely, all BSD) says:=

>=20
> The srand() function sets its argument seed as the seed for a new
> sequence of pseudo-random numbers to be returned by rand().
> These sequences are repeatable by calling srand() with the same seed va=
lue.
>=20
> The Linux manual says:
>=20
> The  srand()  function  sets  its  argument  as the seed for a new
> sequence of pseudo-random integers to be returned by rand().
> These sequences are repeatable by calling srand() with the same seed va=
lue.
>=20
> I would say the expectation here is pretty clear.

Yes, there is plenty of code out there that relies on srand()+rand()
returning a repeatable sequence of pseudo-random numbers. I have written
some myself. C devs are very familiar with this behaviour of srand.
There are tons of uses for this in game-related code. Think of something
like Minecraft world seeds. I bet Minecraft even uses this, or at least
the Java version of this, for generating its worlds. The worlds are
randomly generated, but if you get a particularly cool world you can
check the seed and give that seed to a friend and your friend can get
the same world generated. There are entire web sites dedicated to
sharing cool Minecraft seeds like this.

  https://www.google.com/search?q=3Dminecraft+seeds

-Rasmus


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