Improve this PHP bitfield class for settings/permissions?

Question

I have been trying to figure out the best way to use bitmask or bitfields in PHP for a long time now for different areas of my application for different user settings and pe

Answer 1

Here is my proposal:

value = $value;
    }

    public function getValue() {
        return $this->value;
    }

    public function get($n) {
                return $this->value & $n;
    }

    public function set($n, $new=true) {
        $this->value |= $n;
    }

    public function clear($n) {
        $this->value &= ~$n;
    }

}
?>

As you can see, I used 1, 2, 4, 8, etc (powers of 2) to simplify the calculations. If you map one permission to one bit you have:

0 0 0 0 0 0 0 1 = PERM_READ = 1
0 0 0 0 0 0 1 0 = PERM_WRITE = 2
0 0 0 0 0 1 0 0 = PERM_ADMIN = 4
etc...

Then you can use logic operations, for example you have this initially:

    0 0 0 0 0 0 0 1 = PERM_READ = 1

If you want to add permissions to write, you only need to use the bitwise OR operator:

    0 0 0 0 0 0 0 1 = PERM_READ = 1
OR  0 0 0 0 0 0 1 0 = PERM_WRITE = 2
=   0 0 0 0 0 0 1 1 = both bits enabled R & W

To remove one bit you have to use $value & ~$bit, for example remove the write bit:

    0 0 0 0 0 0 1 1 = both bits enabled R & W
AND 1 1 1 1 1 1 0 1 = Bitwise negated PERM_WRITE
=   0 0 0 0 0 0 0 1 = result, only the R bit

Finally, if you want to test if one bit is enabled the operation you have to AND $value against the PERM_XXX you want to test:

    0 0 0 0 0 0 1 1 = both bits enabled R & W
AND 0 0 0 0 0 0 1 0 = Want to test PERM_WRITE
=   0 0 0 0 0 0 1 0 = result

If the result is not zero you have the permission, otherwise you don't.