Wrong scale for BcMath\Number::div result with big numbers

[Sandritsch91]

Description

The following code:

<?php
// $n1 > 10^10 results in wrong scale
$n1 = new \BcMath\Number('100000000000');
$n2 = new \BcMath\Number('1');
echo $n2->div($n1);

Resulted in this output:

0

But I expected this output instead:

0.00000000001

3v4l.org

PHP Version

PHP 8.4.3

Operating System

Windows 11 Pro 24H2, Linux

[cmb69]

For the given script above, I would say that this is a deliberate design decision (see https://wiki.php.net/rfc/support_object_type_in_bcmath for details). You either need to specify the scale explicitly when calling the method, or rely on the larger scale of either Number; see e.g. https://3v4l.org/pIiCN#v8.4.3.

However, the third output contradicts that. Something doesn't look quite right here.

[SakiTakamachi]

@Sandritsch91
This is the intended behavior.

If do not explicitly specify a scale for div(), or if use an operator, the scale of the result is expanded to the scale of the dividend + 10 (max).

In the example code, even if expand to the maximum, the result is 0, so no expansion takes place.

In the second example of code in your URL, if expand the scale to its maximum, the last digit will be a 1, which gives you 0.0000000001.

If the dividend was 1.0 instead of 1, expanding the scale to the maximum would result in a result scale of 11, so your first example would become:

https://3v4l.org/NrXYa#v8.4.3

@cmb69
Perhaps you misread a zero? The third output looks correct.

[cmb69]

Ah, I've missed

However, in cases such as indivisible division, the BcMath\Number::scale of the result is expanded. Expansion is done only as needed, up to a maximum of +10.

So indeed, not a bug.