Editing Mask (computing) (section)

===Toggling bit values===
So far the article has covered how to turn bits on and turn bits off, but not both at once. Sometimes it does not really matter what the value is, but it must be made the opposite of what it currently is. This can be achieved using the [[Exclusive or|<code>XOR</code> (exclusive or)]] operation. <code>XOR</code> returns <code>1</code> [[if and only if]] an [[odd number]] of bits are <code>1</code>. Therefore, if two corresponding bits are <code>1</code>, the result will be a <code>0</code>, but if only one of them is <code>1</code>, the result will be <code>1</code>. Therefore inversion of the values of bits is done by <code>XOR</code>ing them with a <code>1</code>. If the original bit was <code>1</code>, it returns <code>1 XOR 1 = 0</code>. If the original bit was <code>0</code> it returns <code>0 XOR 1 = 1</code>. Also note that <code>XOR</code> masking is bit-safe, meaning that it will not affect unmasked bits because <code>Y XOR 0 = Y</code>, just like an <code>OR</code>.

Example: Toggling bit values
     10011101   10010101
 XOR '''00001111   11111111'''
   = 10010010   01101010

To write arbitrary 1s and 0s to a subset of bits, first write 0s to that subset, then set the high bits:

   register = (register & ~bitmask) | value;