it is basically an alias gmp_mod.(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)
gmp_div_r — Remainder of the division of numbers
   Calculates remainder of the integer division of
   num1 by num2. The
   remainder has the sign of the num1 argument,
   if not zero.
  
num1The number being divided.
 A GMP object, an int,
 or a string that can be interpreted as a number following the same logic
 as if the string was used in gmp_init() with automatic
 base detection (i.e. when base is equal to 0).
num2
       The number that num1 is being divided by.
      
 A GMP object, an int,
 or a string that can be interpreted as a number following the same logic
 as if the string was used in gmp_init() with automatic
 base detection (i.e. when base is equal to 0).
rounding_mode
       See the gmp_div_q() function for description
       of the rounding_mode argument.
      
The remainder, as a GMP number.
Example #1 gmp_div_r() example
<?php
$div = gmp_div_r("105", "20");
echo gmp_strval($div) . "\n";
?>The above example will output:
5
