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Date: Fri, 17 Oct 2014 20:00:20 +0100
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To: PHP Internals <internals@lists.php.net>
Subject: Re: [PHP-DEV] [RFC] Big Integer Support
From: ajf@ajf.me (Andrea Faulds)


> On 10 Oct 2014, at 22:33, Andrea Faulds <ajf@ajf.me> wrote:
>=20
> The RFC can be found here: https://wiki.php.net/rfc/bigint
>=20
> The patch is, as I mentioned, incomplete. Additionally, there are =
quite a few matters left to be decided (see Open Questions). However, I =
think I should put this formally under discussion now.

I promise not to mail the list for every change I make to this RFC. ;)

But I do have quite a big one to announce. Previously, some issues with =
the GNU Multiple Precision Arithmetic Library (GMP) had been discovered. =
In particular, it is not liberally licensed (LGPL), it only has one set =
of custom allocators, which causes segfaults from other libraries which =
use it because PHP defines its own allocators, and it immediately calls =
an un-hookable abort() in certain failure cases.

I was unaware of any good alternatives, however today I was pointed by =
Chris Wright (DaveRandom) on StackOverflow towards a new possibility: =
LibTomMath. It is liberally licensed (dual-licensed as Public Domain and =
WTFPL), written in pure C, packaged for multiple platforms, and it lacks =
the immediate abort() problem to the best of my knowledge. Plus, it will =
not cause any segfaults when we use custom allocators, as I do not =
believe PHP uses any libraries which use LibTomMath at present. If =
you=92re worried about whether it=92s battle-tested, it=92s used by =
another dynamic language, Tcl.

Because it appears to solve all three major issues with GMP, I am =
currently porting my bigint branch to use it. This is possible because =
the entire implementation of bigints is abstracted, meaning you can swap =
out back-ends. If we wished to, we could quite simply allow the choice =
of GMP at compile-time, or indeed any other back-end.

I should note that LibTomMath certainly isn=92t perfect. I don=92t =
believe it is optimised to the same degree GMP is. That being said, =
again, it does seem to solve all the major problems I had with GMP. So I =
have few qualms in making the patch use it, especially given that it is =
easy to swap out the back-end.

I=92ve updated the RFC to reflect this new state of affairs: =
https://wiki.php.net/rfc/bigint

Thoughts?
--
Andrea Faulds
http://ajf.me/