Bitfun: Popcount, Sideways sum, Hamming weight
I was going through some simple coding puzzles yesterday night and became fascinated by this seemingly interesting function:
int CountBits (unsigned int x ) {
static unsigned int mask[] = {
0x55555555,
0x33333333,
0x0F0F0F0F,
0x00FF00FF,
0x0000FFFF
};
int i ;
int shift ; /* Number of positions to shift to right*/
for (i = 0, shift = 1; i < 5; i++, shift *= 2)
x = (x & mask[i]) + ((x >> shift) & mask[i]);
return x;
}
