Error in round() and number_format()

[joaopalopes24]

Description

I have this code:

<?php

addAmount(50.00, 'update', 112.99);

function addAmount(float $addedValue, ?string $type, float $baseAmount): string
{
    if ($addedValue) {
        $baseAmount += $type == 'fixed' ? $addedValue : $baseAmount / 100 * $addedValue;
    }


    var_dump(
        $baseAmount,
        round($baseAmount, 2),
        number_format(169.485, 2, '.', ''),
        number_format($baseAmount, 2, '.', ''),
    );

    return number_format($baseAmount, 2, '.', '');
}

In PHP 8.3, If I run this code, the result is:

float(169.48499999999999)
float(169.49)
string(6) "169.49"
string(6) "169.49"

But if I run this same code in PHP 8.4, the result is:

float(169.48499999999999)
float(169.48)
string(6) "169.49"
string(6) "169.48"

PHP Version

8.4.3

Operating System

Ubuntu 22.04

[iluuu1994]

/cc @SakiTakamachi

[cmb69]

From https://www.php.net/manual/en/migration84.other-changes.php#migration84.other-changes.functions.standard:

Fixed a bug caused by "pre-rounding" of the round() function. Previously, using "pre-rounding" to treat a value like 0.285 (actually 0.28499999999999998) as a decimal number and round it to 0.29. However, "pre-rounding" incorrectly rounds certain numbers, so this fix removes "pre-rounding" and changes the way numbers are compared, so that the values are correctly rounded as decimal numbers.

The maximum precision that can be handled by round() has been extended by one digit. For example, round(4503599627370495.5) returned in 4503599627370495.5, but now returns 4503599627370496.

So yes, there have been changes to rounding, but you shouldn't rely on either detail. After all, floating point values are not precise, and you never ever use them for monetary calculations anyway.

[SakiTakamachi]

@joaopalopes24

169.48499999999999 is less than 169.485, so it rounds to 169.48.

So 8.4 behavior is correct.

This was a bug in versions up to 8.3 and was fixed in 8.4.

https://www.php.net/manual/en/migration84.other-changes.php

However, this fix was not backported because it would cause a BC break in an edge case.

edit:
The label became strange due to a time lag, so I restored it.