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Date: Fri, 12 Jul 2024 13:24:54 +0200
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To: PHP Internals <internals@lists.php.net>
Subject: [PHP-DEV] Breaking change of rounding behavior in PHP 8.4
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From: cmbecker69@gmx.de ("Christoph M. Becker")

Hi all,

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.

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.

What do you think?

[1] <https://github.com/php/php-src/pull/12222>
[2] <https://github.com/php/php-src/issues/14332>

Cheers,
Christoph