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Date: Tue, 1 Jun 2021 23:28:05 +0900
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To: PHP internals <internals@lists.php.net>
Cc: Nikita Popov <nikita.ppv@gmail.com>, Guilliam Xavier <guilliam.xavier@gmail.com>, 
	Dan Ackroyd <Danack@basereality.com>, Kamil Tekiela <tekiela246@gmail.com>, 
	Rowan Tommins <rowan.collins@gmail.com>, =?UTF-8?Q?Alexandru_P=C4=83tr=C4=83nescu?= <drealecs@gmail.com>
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Subject: [RFC] Under Discussion: Add Random class and RandomNumberGenerator interface
From: zeriyoshi@gmail.com (Go Kudo)

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Hello internals.
Thanks for continuing to participate in the discussion.

I've sorted out the proposal, and finished writing and implementing the RFC.
(Funny, I know.) I think it's time to start a discussion.

https://wiki.php.net/rfc/rng_extension
https://github.com/php/php-src/pull/7079

The main changes since last time are as follows:

- The ugly RANDOM_USER has been removed.
- RandomNumberGenerator interface has been added for user-defined RNGs.
- Random class is now final.
- Random class now accepts a RandomNumberGenerator interface other than
string as the first argument to the constructor.
- INI directive has been removed. In 32-bit environments, the result is
always truncated.

What I'm struggling with now is the behavior when calling nextInt() in a
32-bit environment using a 64-bit RNG. It currently returns a truncated
result, which means that the code loses compatibility with the result of
running on a 64-bit machine.
I was also considering throwing an exception, but which would be preferable?

I would like to answer a few unanswered questions.

> What is bias?

I' ve confirmed that the bias issue in mt_rand has already been fixed and
is no longer a problem.

This implementation copies most of it from mt_rand. Therefore, this problem
does not exist.

Therefore, an equivalent method to mt_getrandmax() is no longer provided.

> uint64 & right-shift

This is a specification of the RNG implementation. PHP does not have
unsigned integers, but RNG handles unsigned integers (to be precise, even
the sign bit is random).

As mentioned above, PHP does not have unsigned integers, which means that
using the results generated by RNGs may cause compatibility problems in the
future. To avoid this, a 1-bit right shift is always required (similar to
mt_rand()).

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