LeetCode "Number of 1 Bits"

Counting number of enabled bits in uint32_t.. Here is a O(lg32) solution. Very smart, like bottom-up parallel tree post-order traversal.

Solution from discussion of LC:

int hammingWeight(uint32_t n) 
{
    n = ((n >> (1 << 0)) & 0x55555555) + (n & 0x55555555);
    n = ((n >> (1 << 1)) & 0x33333333) + (n & 0x33333333);
    n = ((n >> (1 << 2)) & 0x0F0F0F0F) + (n & 0x0F0F0F0F);
    n = ((n >> (1 << 3)) & 0x00FF00FF) + (n & 0x00FF00FF);
    return ((n >> (1 << 4)) & 0xFFFF) + (n & 0xFFFF);
}