PHP 8.4.2 wrong round()

[akademic]

Description

The following code:

<?php
$numerator = 7380;
$denominator = 28800;
$precision = 2;
$result = round(($numerator / $denominator) * 100, $precision);

echo $result;

Resulted in this output:

25.62

But I expected this output instead:

25.63

Without round we get 25.625, so after round it must be 25.63

PHP Version

PHP 8.4.2

Operating System

No response

[devnexen]

If that helps, see this one #17136

[remicollet]

I don't see anything wrong

$ php -r 'var_dump($a = 7380 / 28800 * 100, round($a, 2));'
float(25.624999999999996)
float(25.62)

25.624999999999996 is properly rounded to 25.62

PHP 8.4 is right here
Indeed 8.3 give a different result

Behavior change is documented
https://www.php.net/manual/en/migration84.other-changes.php

[remicollet]

Notice teh behavior have changed in 5.2.7 (yes, quite old)
as fixing https://bugs.php.net/bug.php?id=42294
sadly, cannot find the commit... lost during github migration....

[remicollet]

Floating arithmetic fun:

$ php84 -r 'var_dump($a=round(7380/28800*100,2));'
float(25.62)
$ php84 -r 'var_dump($a=round(7380*100/28800,2));'
float(25.63)

[cmb69]

My favorite is still 0.1 + 0.2 != 0.3.

[urmas-lipso]

also found this fun situation:
echo (10.075 / 0.05) . ' - ' . round(10.075 / 0.05) . ' - ' . round(201.5);
giving results
with 8.4.x 201.5 - 201 - 202
with 8.2.x and 8.3.x 201.5 - 202 - 202
note the different number in the middle

[TimWolla]

10.075 actually is 10.0749999999999992895 and 0.05 actually is 0.0500000000000000027756. The division between those is 201.499999999999971578, which is different than 201.5 (which is the next-higher float).

[urmas-lipso]

presumed something like this, but the problem is result being different for 8.3 and 8.4, that will cause problems while upgrading