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Date: Tue, 7 Sep 2021 10:28:19 +0200
Message-ID: <CAF+90c-j84_gXvnChewQoJbHnGLWgcHfszp=GgFF8_sAaPahdA@mail.gmail.com>
To: Go Kudo <zeriyoshi@gmail.com>
Cc: PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="0000000000004133c005cb638d3e"
Subject: Re: [PHP-DEV] [RFC] Random Extension 3.0
From: nikita.ppv@gmail.com (Nikita Popov)

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On Thu, Sep 2, 2021 at 5:10 PM Go Kudo <zeriyoshi@gmail.com> wrote:

> Hi Internals.
>
> Expanded from the previous RFC and changed it to an RFC that organizes the
> whole PHP random number generator. Also, the target version has been
> changed to 8.2.
>
> https://wiki.php.net/rfc/rng_extension
> https://github.com/php/php-src/pull/7453
>
> Hopefully you will get some good responses.
>

This RFC currently tries to keep some semblance of compatibility with the
existing mt_rand() algorithm by retaining the same implementation for
mapping the raw random number stream into a range. However, the algorithm
we use for that is not exactly state of the art and requires two full-width
divisions at minimum. There are more efficient scaling algorithms based on
fixed-point multiplication, which are "nearly divisionless" (
https://arxiv.org/pdf/1805.10941.pdf). The variant at
https://github.com/apple/swift/pull/39143 is entirely divisionless.

Doing this would improve performance (though I'm not sure by how much --
maybe once we add up our call overhead, it isn't important anymore?) but it
would provide a different sequence than mt_rand(). Something we might want
to consider.

Regards,
Nikita

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