What is the most hard to understand piece of C++ code you know?

The inverse square root implementation in Quake 3:

float InvSqrt (float x){
    float xhalf = 0.5f*x;
    int i = *(int*)&x;
    i = 0x5f3759df - (i>>1);
    x = *(float*)&i;
    x = x*(1.5f - xhalf*x*x);
    return x;
}

Update: How this works (thanks ryan_s)

I know it's C and not C++ but there is always the the International Obfuscated C Code Contest. I have seen some code there that would make your head spin.

Duff's Device (http://en.wikipedia.org/wiki/Duff%27s_device) give me nightmares:

strcpy(to, from, count)
char *to, *from;
int count;
{
    int n = (count + 7) / 8;
    switch (count % 8) {
    case 0: do { *to = *from++;
    case 7:      *to = *from++;
    case 6:      *to = *from++;
    case 5:      *to = *from++;
    case 4:      *to = *from++;
    case 3:      *to = *from++;
    case 2:      *to = *from++;
    case 1:      *to = *from++;
            } while (--n > 0);
    }
}

This was on reddit recently http://www.eelis.net/C++/analogliterals.xhtml

 assert((o-----o
        |     !
        !     !
        !     !
        !     !
        o-----o ).area == ( o---------o
                            |         !
                            !         !
                            o---------o ).area );