Gamevar operators
From EDukeWiki
<operator>var <gamevar> <value>
<operator>varvar <gamevar> <value>
Gamevar operators are commands that perform various mathematical and bitwise logical operations on gamevars. The first argument must be a writable gamevar and is taken as the destination as well and the first operand (2address code).
For example:
setvar temp 1 // assigns a value of 1 to the gamevar temp. addvar temp 1 // adds 1 to temp, causing its value to become 2. mulvar temp 2 // multiplies temp by 2, causing its value to become 4.
Operator  C/C++  Math  Description  Notes  

set  =

=  assignment  
add  +

+  addition  
sub  

–  subtraction  
mul  *

×  multiplication  
div  /

÷  division with rounding toward 0 for nonnegative dividends  Ensure that <value> does not equal 0 at any time. The rounding behavior is undefined for negative dividends.  
mod  %

modulo, remainder  Ensure that <value> does not equal 0 at any time; sign of the result is that of left hand side operand (dividend).  
and  &

bitwise AND  The bits in the result are set only if they were set in both of the values being operated on. Ex. (all numbers are base2): 01001010 AND 11110100 is 01000000  
or  

bitwise OR  The bits in the result are set only if they were set in either of the values being operated on. Ex.: 01001010 OR 11110100 is 11111110  
xor  ^

bitwise XOR  The bits in the result are set if only one of the values being operated on has those bits set. Ex.: 01001010 XOR 11110100 is 10111110 
Commands with an additional "var" suffix take gamevars rather than constants or defined labels for their inputs.