Edit report at https://bugs.php.net/bug.php?id=64450&edit=1
ID: 64450
Comment by: ab@php.net
Reported by: stefano dot baccianella at gmail dot com
Summary: mt_rand causes overflow within certain max value
Status: Wont fix
Type: Bug
Package: *General Issues
Operating System: Windows 7 64bit
PHP Version: 5.4.13
Assigned To: ab
Block user comment: N
Private report: N
New Comment:
Linux or BSD 64 bit i mean.
Previous Comments:
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[2013-03-26 19:44:39] ab@php.net
Well, Windows stands completely alongside. long on both x86 and x64 Windows is 32
bit, so no matter which PHP build is used. The code we deal with here only works
correct on system having sizeof(long) >= sizeof(double), that are for instance 64
bit Linux or BSD.
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[2013-03-26 08:11:43] stefano dot baccianella at gmail dot com
Yeah, true. I was misled by the fact that my system is 64bit but PHP for windows
is compiled on 32bit.
I think that an RFC for 5.6 should be enough.
Thank you
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[2013-03-25 23:22:53] ab@php.net
I'm not sure something like that would be accepted as the valid domain is clearly
documented and such a change is still a BC breach. What might work is a change
request including an RFC for 5.6, otherwise a PECL ext.
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[2013-03-25 20:47:13] stefano dot baccianella at gmail dot com
Ok, now it's clear.
Maybe as a minor fix I can suggest to check if MAX is greater than PHP_INT_MAX and
return a value instead of an error (FALSE value?) or an error with an explanation,
in both cases it's better than an overflow.
Thank you very much for your time
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[2013-03-25 20:40:52] ab@php.net
Please consider the following snippet
while(true) {
$max = pow(10, 13); // 10000000000000
$rand = mt_rand(0, $max);
if ($rand > PHP_INT_MAX) {
break;
}
}
It *seems* to work, but you'll never reach the break condition. On some systems that
might be PHP_INT_MAX*2, not sure. Thus, the whole range between pow(10, 13) and
PHP_INT_MAX will never be returned.
Additionally please be aware - we deal with a pseudo randomness here, it works as
expected in 32 bit range only with 32 bit long. The implementation seems to run
unexpected overflows on some places like pow(10, 12) you've reported, but it just
physically won't work with floats.
Thanks for reporting. A better solution is definitely needed for this functionality,
not just a bug fix.
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