Hilarious [Or Not So Hilarious] Code Optimizations

Question

Raymond Chen has this to say on his recent post on code optimizations... Obvious optimizations - one that begs to be optimized - tend to be \"de-optimizations\" if you conside

Answer 1

My favorite example would be the XOR swap algorithm:

// swap these two values:
int x = 4;
int y = 2;

// original:
int temp = x;
x = y;
y = temp;

// optimized version:
x ^= y;
y ^= x;
x ^= y;

Yes, it uses no temporary variable, and can usually be done in three processor cycles, but it sure isn't obvious what it does!