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(PHP 7)
intdiv — Integer division
$dividend 
    ,  int $divisor 
    )
   Returns the integer quotient of the division of dividend by divisor.
  
dividend Number to be divided.
divisor 
      Number which divides the dividend.
     
   The integer quotient of the division of dividend by divisor.
  
    If divisor is 0, a DivisionByZeroError
    exception is thrown. If the dividend is  PHP_INT_MIN 
    and the divisor is -1, then an
    ArithmeticError exception is thrown.
  
Example #1 intdiv() example
  <?php
var_dump ( intdiv ( 3 ,  2 ));
 var_dump ( intdiv (- 3 ,  2 ));
 var_dump ( intdiv ( 3 , - 2 ));
 var_dump ( intdiv (- 3 , - 2 ));
 var_dump ( intdiv ( PHP_INT_MAX ,  PHP_INT_MAX ));
 var_dump ( intdiv ( PHP_INT_MIN ,  PHP_INT_MIN ));
 var_dump ( intdiv ( PHP_INT_MIN , - 1 ));
 var_dump ( intdiv ( 1 ,  0 ));
 ?>   int(1) int(-1) int(-1) int(1) int(1) int(1)Fatal error: Uncaught ArithmeticError: Division of PHP_INT_MIN by -1 is not an integer in %s on line 8 Fatal error: Uncaught DivisionByZeroError: Division by zero in %s on line 9
[#1] polettog at gmail dot com [2015-07-31 09:34:23]
Without intdiv(), the following may be a good way (with $a and $b of type integer and not too big) :
<?php
(int)($a / $b)
?>
because in case of divisible integers, the result will be integer and there is no risk of float appearing round but below their represented value (like the case (0.1+0.7)*10).
$a and $b really needs to be of type integer though. 
If they are too big and indivisible, some precision will be lost during the conversion to float and the result may be inaccurate.
[#2] AmeenRoss [2015-07-11 13:15:50]
This does indeed seem to be equal to intdiv:
<?php
function intdiv_1($a, $b){
    return ($a - $a % $b) / $b;
}
?>
However, this isn't:
<?php
function intdiv_2($a, $b){
    return floor($a / $b);
}
?>
Consider an example where either of the parameters is negative:
<?php
$param1 = -10;
$param2 = 3;
print_r([
    'modulus' => intdiv_1($param1, $param2),
    'floor' => intdiv_2($param1, $param2),
]);
?>
[#3] Ts.Saltan [2015-06-16 20:53:37]
$a = 57;
$b = 3;
var_dump(
	intdiv($a,$b),
	intdiv_1($a,$b),
	intdiv_2($a,$b)
);
function intdiv_1($a, $b){
	return ($a-$a%$b)/$b;
}
function intdiv_2($a, $b){
	return floor($a/$b);
}
//intdiv($a, $b) == floor($a/$b) == ($a-$a%$b)/$b