Bitwise operations in PHP?

Question

I understand that bitwise operations are necessary for much low-level programming, such as writing device drivers, low-level graphics, communications protocol packet assembly and decoding. I have been doing PHP for several years now, and I have seen bitwise operations very rarely in PHP projects.

Can you give me examples of usage?

Answer 1

You could use it for bitmasks to encode combinations of things. Basically, it works by giving each bit a meaning, so if you have 00000000, each bit represents something, in addition to being a single decimal number as well. Let's say I have some preferences for users I want to store, but my database is very limited in terms of storage. I could simply store the decimal number and derive from this, which preferences are selected, e.g. 9 is 2^3 + 2^0 is 00001001, so the user has preference 1 and preference 4.

 00000000 Meaning       Bin Dec    | Examples  │││││││└ Preference 1  2^0   1    | Pref 1+2   is Dec   3 is 00000011  ││││││└─ Preference 2  2^1   2    | Pref 1+8   is Dec 129 is 10000001  │││││└── Preference 3  2^2   4    | Pref 3,4+6 is Dec  44 is 00101100  ││││└─── Preference 4  2^3   8    | all Prefs  is Dec 255 is 11111111  │││└──── Preference 5  2^4  16    |  ││└───── Preference 6  2^5  32    | etc ...  │└────── Preference 7  2^6  64    |  └─────── Preference 8  2^7 128    | 

Further reading

• http://www.weberdev.com/get_example-3809.html
• http://stu.mp/2004/06/a-quick-bitmask-howto-for-programmers.html
• Why should I use bitwise/bitmask in PHP?
• http://en.wikipedia.org/wiki/Mask_%28computing%29

Answer 2

Bitwise operations are extremely useful in credentials information. For example:

function is_moderator($credentials) { return $credentials & 4; }  function is_admin($credentials) { return $credentials & 8; } 

and so on...

This way, we can keep a simple integer in one database column to have all credentials in the system.