Bitwise operations in PHP?

29
votes

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?

2
phpbit-manipulation
Very little in PHP uses bitwise operations outside of optimization tricks as well as configuration such as php.net/manual/en/function.error-reporting.php – Ignacio Vazquez-Abrams
Check below link for more details phpchef.com/posts/php-bitwise-operators – Abutouq

2 Answers

47
votes

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

18
votes

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.