gistfile1.txt

roles

role   | description
-------------------------
15     | admin
5      | user
9      | guest


rights

right  | description
-------------------------
2		   | can add posts
4		   | can del posts
8		   | can comment
16		 | can edit
32		 | can fly
64		 | can eat

15 = 1|2|4|8
15 & (2 or 4 or 8) !== 0 ==> has access
15 & (16 or 32 or 64 or ...) === 0 ==> hasn't access

5 = 1|4
5 & (4) !== 0
5 & (2,8,16,32, ...) === 0

9 = 1|8

function check($role,$right){
	return !!($role & $right);
}

check(15,2) => true
check(15,16) => false