'How is -13 % 64 = -13 in PHP?

Derived from this question : (Java) How does java do modulus calculations with negative numbers?

Anywhere to force PHP to return positive 51?

update
Looking for a configuration setting to fix, instead hard-guessing

Or other math function like bcmath?

updated
Not entire convinced by that java answer, as it does not take account of negative modulus -13+(-64) =?

phpmathmodulus


Solution 1:[1]

Anyway, the post you referenced already gave the correct answer:

$r = $x % $n;
if ($r < 0)
{
    $r += abs($n);
}

Where $x = -13 and $n = 64.

Solution 2:[2]

The modulo operation should find the remainder of division of a number by another. But strictly speaking in most mainstream programming languages the modulo operation malfunctions if dividend or/and divisor are negative. This includes PHP, Perl, Python, Java, C, C++, etc.

Why I say malfunction? Because according to mathematic definition, a remainder must be zero or positive.

The simple solution is to handle the case yourself: 

if r < 0  then r = r + |divisor|;

|divisor| is the absolute value of divisor.

Another solution is to use a library (as @Gordon pointed). However I wouldn't use a library to handle a simple case like this.

Solution 3:[3]

I hate using if in this case when you can calculate it right away.

$r = ($x % $n + $n) % $n;

when $n is positive.

Solution 4:[4]

The PHP manual says that

The result of the modulus operator % has the same sign as the dividend — that is, the result of $a % $b will have the same sign as $a. For example

so this is not configurable. Use the options suggested in the question you linked to

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1
Solution 2 Nylon Smile
Solution 3 Anurat Chapanond
Solution 4 Gareth

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