PHP Manual: Get modulus of an arbitrary precision number

string bcmod(string $num1, string $num2, intnull $scale = null)

Get the remainder of dividing num1 by num2. The result has the same sign as num1.

num1: The left operand, as a string.
num2: The right operand, as a string.
scale: This parameter is used to set the number of digits after the decimal place in the result. If null, it will default to the default scale set with bcscale, or fallback to the value of the bcmath.scale INI directive.

Returns the modulus as a string.

This function throws a ValueError in the following cases:

This function throws a DivisionByZeroError exception if num2 is 0.

Version	Description
8.0.0	`scale` is now nullable.
8.0.0	Dividing by `0` now throws a DivisionByZeroError exception instead of returning null.
7.2.0	`num1` and `num2` are no longer truncated to integer, so now the behavior of bcmod follows fmod rather than the `%` operator.
7.2.0	The `scale` parameter was added.

Example #1 bcmod example

<?php
bcscale(0);
echo bcmod( '5',  '3'); //  2
echo bcmod( '5', '-3'); //  2
echo bcmod('-5',  '3'); // -2
echo bcmod('-5', '-3'); // -2
?>

Example #2 bcmod with decimals

<?php
bcscale(1);
echo bcmod('5.7', '1.3'); // 0.5 as of PHP 7.2.0; 0 previously
?>

bcmod