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 Description: | Most people don't see the potential of bitwise in Lua or even know it exists in Lua. This article aims to explain a bit about bitwise and how to use it. |
 Original Author: | Butt Face |
 Created: | 22th April 2008 |
What is a bitwise?
- Bitwise is a set of operators that act on the binary level of a number.
Available Operators
| OR
& AND
<< Bit shift left
>> Bit shift right
Example
local a, b, c, d, e = 1, 2, 4, 8, 16;
local sum = b | e; // 18
local value = e;
if( sum & value == value )then
// Our value is in the sum.
end
- This example may be very overwhelming for bitwise newcomers. But it is only meant to show a very basic use of bitwise operators.
Real world example
- You ask "When the hell would I ever use this in Lua?", well, you might use it to check if a player has access to do a certain thing.
// Each of these must be a power of 2
local kick = 1;
local ban = 2;
local pee = 4;
local weapons = 8;
local user_flags = kick | weapons; // 9
// Check if a user has access to kick
if( user_flags & kick == kick )then
// User has this flag.
end
How does it work?
Here's what happens when you use the OR operator in the previous example kick | weapons :
00000001 //This is 1 in binary
00001000 //And this is 8 in binary
-------- //Using the OR operator, if any of the bits are 1 they will be 1 in the result.
00001001 //This is 9 in binary.
And now for user_flags & kick :
00001001 //This is user_flags( 9 ) in binay
00000001 //And this is kick( 1 ) in binary
-------- //Using the AND operator, if both of the bits are 1 they will be in the result.
00000001 //This is the result of the operation (1) and it is equal to kick which was also 1.
Additional Notes
- Bitwise operators are only available in the Garry's Mod Lua environment, although there are modules that add bitwise functions.
- Hammer uses bitwise to store and retrieve spawnflags. To set them use ent:Fire( "spawnflags", "num" ) where "num" is the value of the flags you want.
- More information on bitwise operators can be found at http://en.wikipedia.org/wiki/Bitwise_operation
- A very helpful tutorial on bitwise (directed towards PHP, but can be easily applied to Lua as well) can be found at http://www.litfuel.net/tutorials/bitwise.htm
- The bitshift, << and >>, operators only seem to work with constants. To get around this, you can use the RunString function.
- This may not be true anymore, with the recent update(November 3rd), they now work with variables.
