CODEWITHSUNDEEP
c++booleanbitwise-operatorsboolean-operationsbitwise-xor
Ellie Dunstan
Ellie Dunstan

Reputation: 43

Understanding bitwise XOR (^) with boolean variables

I'm from a game programming background and I've just come across a bitwise XOR ^. I've seen examples of how it works with integers, but I'm a bit confused about the result with boolean values. I know a bool is either 0 or 1, but after testing I haven't been able to replicate the ^ result with simple operators. Could someone please explain to me what the following code snippet (specifically the ^) is doing? Many thanks.

bool body1awake = rigidbody1.isAwake;
bool body2awake = rigidbody2.isAwake;
if (body1awake ^ body2awake)
{
    if (body1awake) rigidbody2.SetAwake();
    else rigidbody1.SetAwake();
}

Upvotes: 2

Views: 909

Answers (2)

Bathsheba
Bathsheba

Reputation: 234665

As bool is a narrower type than an int, both arguments are implicitly converted to an int prior to the XOR being evaluated. true assumes the value 1, and false assumes the value 0.

If that result is non-zero then the if body runs, and that happens if and only if body1awake is not equal to body2awake.

So perhaps the equivalent

if (body1awake != body2awake)

would have been better. If the author thinks their way is faster then they need a stern talking to with compiler optimisations and as-if rule being introduced into the conversation.

Upvotes: 2

NathanOliver
NathanOliver

Reputation: 180500

Exclusive or of two bits is true when only one of them is set. If both are set or not set then it is false. Since bool basically represents a single bit (0 or 1 are its only values)

if (body1awake ^ body2awake)

means that the condition will be true on when body1awake != body2awake.

Upvotes: 3

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