Why should I use bitwise/bitmask in PHP?

Question

I am working on a user-role / permission system in PHP for a script.

Below is a code using a bitmask method for permissions that I found on phpbuilder.com.

B

Answer 1

Edit: rereading the question, it looks like the user's permissions are coming back from your database in a bitfield. If that's the case, you are going to have to use bitwise operators. A user who's permission in the database is 5 has PERMISSION_READ and PERMISSION_DENIED because (PERMISSION_READ & 5) != 0, and (PERMISSION_DENIED & 5) != 0. He wouldn't have PERMISSION_ADD, because (PERMISSION_ADD & 5) == 0

Does that make sense? All the complex stuff in your bitwise example looks unnecessary.

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If you don't fully understand bitwise operations, then don't use them. It will only lead to lots of headaches. If you are comfortable with them, then use them where you feel they are appropriate. You (or whoever wrote the bitwise code) doesn't seem to fully grasp bitwise operations. There are several problems with it, like the fact that the pow() function is used, that would negate any kind of performance benefit. (Instead of pow(2, $n), you should use the bitwise 1 << $n, for example.)

That said, the two pieces of code do not seem to do the same things.