1, 2, 4, 8, 16, 31, 64, 128, 256, 1024, etc... (you should recognize this pattern)

Now comes the part where you determine what "BITS" are on and which are off.

Let's call the variable that holds this value "permissions".

So, lets say that the value contained in $permissions is 9. this means that the permission with the value of 1 and the permission with the value of 8 are on.

this line will detect if the "1 BIT is on"

if ($permissions&1)

What it does is this. We do a binary AND of $permissions & 1. If the 1 Bit is on the expression will return an non zero value which evaluates as true. If the 1 Bit is off then 0 is returned and the expression evaluates as false.

The same can be done at any level

if ($permissions&8) will return true (actually 8) if the 4th bit is on and false (0) if it is off.

Hopefully that helps and is at least close to what you are looking for. Let me know if you have any questions.