Question

I’m working with a system that uses the following permission scheme:

1 – Permission A

2 – Permission B

4 – Permission C

8 – Permission D

16 – Permission E

The permissions for a user is stored as the sum of the permission values. For example, if a user has permissions B, C, and D, 14 is the number that is stored. (2+4+8)

Is there a fast way to find out if the user has permission D that doesn’t involve a full expansion of the permission string? (Taking a power of two until greater than the stored number, subtracting off that power, until the target number is reached)

Answer 1

http://php.net/manual/en/language.operators.bitwise.php

$has_D = $perms & 8;

or

$has_Nth_perm = $perms & (1 << ($n-1));

or

function has_nth_perm($perms, $n) {
    return $perms & (1 << ($n-1));
}