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srand(0) set random seed to 0 instead random #10292
Description
Description
The following code:
<?php
function foo(): int
{
srand(0);
$bar = rand(0, 1023);
var_dump($bar);
return $bar;
}
var_dump(foo() === foo());Resulted in this output:
int(684)
int(684)
bool(true)
But I expected this output instead:
int(23)
int(756)
bool(false)
But this code:
<?php
function foo(): int
{
srand();
$bar = rand(0, 1023);
var_dump($bar);
return $bar;
}
var_dump(foo() === foo());Works fine:
int(722)
int(132)
bool(false)
https://www.php.net/manual/en/function.srand.php
Seeds the random number generator with seed or with a random value if seed is 0.
It's seems like srand(0) process 0 as new seed value instead 0 must reset seed to new random value.
PHP Version
PHP 8.2.0
Operating System
Win 11 build 25272 (insider)
Activity
hormus commentedon Jan 11, 2023
From php >= 4.3.0 expected result bool true
mt_srand(0) From php >= 7.1.0 expected result bool true
https://3v4l.org/JNHF8
damianwadley commentedon Jan 11, 2023
The srand page is a bit weird because it seems to try to document a function that doesn't exist anymore: it's mt_srand now, and that does not do the "with a random value if seed is 0" behavior. And given that 3v4l, it seems the original rand didn't actually do this?
Either way this seems like a documentation issue.
cmb69 commentedon Jan 11, 2023
The docs mention that
srand()is an alias ofmt_srand()as of PHP 7.1.0, and since the docs are currently supposed to document PHP 7.0 - 8.2, that looks okay.Anyhow, the problem is that the stubs are not matching the implementation; the stubs claim the default of
$seedwould be zero:php-src/ext/random/random.stub.php
Line 19 in 4427b2e
However, actually the implementation just checks whether an argument has been passed, or not:
php-src/ext/random/random.c
Line 691 in 4427b2e
So there is no default value.
So back to php-src. Documentation should be fixed afterwards.
cmb69 commentedon Jan 11, 2023
The big question is how to solve this: fix the stubs (resulting in a painful signature), or fix the implementation (resulting in a BC break). @kocsismate, thoughts?
cmb69 commentedon Jan 11, 2023
Ah, and since this is now part of ext/random, maybe @zeriyoshi and @TimWolla have thoughts on this as well.
TimWolla commentedon Jan 11, 2023
I do have thoughts on this: The only good reason to use
mt_rand()andmt_srand()in the first place since PHP 7.0 is getting a reproducible sequence, thus changing the long-standing behavior of0is a no-go in my book, especially since this would either also affect the OOP Mt19937 engine or result in differences between Mt19937 and mt_rand, which directly goes against the intended behavior.I suggest to change the actual default value to
null, like Mt19937's default isnullas well and makenullequivalent to a random uint32_t.adic3x commentedon Jan 11, 2023
https://www.php.net/manual/en/function.mt-srand.php
Ok, but it factually contradicts to signature of this function:
Where default value of $seed is 0. And I expect
mt_srand();andmt_srand(0);must works identically. For example, if I declare somefunction foo(int $ i = 0)thenfoo();andfoo(0);works identically.As for me
looks more intuitive. For example
substrtakes int or null:6 remaining items
Girgias commentedon Jan 12, 2023
No the documentation should reflect the actual implementation in this case. So the issue is more related to the docs lying currently.
kocsismate commentedon Jan 19, 2023
I agree with making the default value
null, but I think we should only fix this in master due to the BC break, shouldn't we? The BC break is very unfortunate, but we changed quite many similar signatures in the past, so this shouldn't be too big of an issue, especially because the documentation clearly states that the parameter is anintright now, and the description is correct about when the automatic seed is applied (when no parameter is given).Fix GH-10292 make the default value of the first parame of srand() an…
Fix phpGH-10292 1st param of mt_srand() has UNKNOWN default on PHP <8.3
Fix GH-10292 1st param of mt_srand() has UNKNOWN default on PHP <8.3
Merge branch 'PHP-8.1' into PHP-8.2
Merge branch 'PHP-8.2'