His solution for 32-bit integers:

v = v - ((v >> 1) & 0x55555555); // reuse input as temporary v = (v & 0x33333333) + ((v >> 2) & 0x33333333); // temp c = ((v + (v >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; // count

Compare that to the algorithm from K&R C:

long count_bits(long n) { unsigned int c; // c accumulates the total bits set in v for (c = 0; n; c++) n &= n - 1; // clear the least significant bit set return c; }

K&R's solution makes sense to me. The other one is insane. Will try both in Go and see which wins.