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Date: Fri, 12 Jul 2024 14:10:28 +0000
To: "Christoph M. Becker" <cmbecker69@gmx.de>
Cc: PHP Internals <internals@lists.php.net>
Subject: Re: [PHP-DEV] Breaking change of rounding behavior in PHP 8.4
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From: internals@gpb.moe ("Gina P. Banyard")

On Friday, 12 July 2024 at 12:24, Christoph M. Becker <cmbecker69@gmx.de> w=
rote:

> Hi all,
>=20
> there has been a "small" change in the rounding logic of
> _php_math_round()[1] a couple of months ago. A respective ticket,
> claiming the new behavior would be a bug[2] had been filed a while ago
> without proper triage so far. I'm bringing this to your attention,
> because I'm afraid that there will be (many) more bug reports about this
> in the future (note that the change only affects master, and only PHP
> 8.4.0alpha1 has been released yet, so it is probably not widespreadly
> tested yet). At the very least we should be sure that we want to keep
> this change, and document it well, to avoid discussions in every filed
> ticket.
>=20
> My personal stance on this is simple: floating point arithmetic is not
> exact per se, and changes to how PHP handles the details should only be
> introduced, if they clearly improve things. This change apparently
> improves some cases, but worsens others. Thus, I think the change
> should better be reverted, and if at all, postponed to PHP 9, since I
> neither regard this change as bug fix nor as a feature.
>=20
> What do you think?
>=20
> [1] https://github.com/php/php-src/pull/12222
>=20
> [2] https://github.com/php/php-src/issues/14332

I agree, this situation is extremely suboptimal.

My understanding as to why people declined the "Change the edge case of rou=
nd()" RFC [1] was because they were worried about the silent change in beha=
viour.
However, most people seem to have missed the fact, myself included, that re=
gardless of it being accepted or not there would have been changes to the b=
ehaviour.
As such we have the worst of both worlds, continuing to have incorrect floa=
ting point semantics for people that rely on proper IEEE 754 floating point=
s,
and yet we still have a silent change in behaviour due to the partial bugfi=
x.

Moreover, these fixes made the implementation of round() more complicated, =
for marginal benefits IMHO.=20

Best regards,

Gina P. Banyard

[1] https://wiki.php.net/rfc/change_the_edge_case_of_round