Reversing logic in condition

Let's say there's a function.
function foo($a, $b, $reverse = false) { if ($a > $b) return $a  $b; else return $a + $b; }
We need to make sure,
$reverse == true
the result of the logical operation was provided that it was, in lieu of($a > $b)
It's gone.!($a > $b)
♪ This operation needs to be introduced.

Special for cases like yours, there is an operator. https://ru.wikipedia.org/wiki/%D0%A1%D0%BB%D0%BE%D0%B6%D0%B5%D0%BD%D0%B8%D0%B5_%D0%BF%D0%BE_%D0%BC%D0%BE%D0%B4%D1%83%D0%BB%D1%8E_2 known as Excluding "or"♪
The result of the operation is true at that time and only then, When only one of the arguments is true.
In your case, it's very simple:
if ($a > $b ^ $reverse) return $a  $b; else return $a + $b;