If you insist, you could calculate the log2 as something like x |= x >> 1; x |= x >> 2; x |= x >> 4; x |= x >> 8; x |= x >> 16; ret

If you insist, you could calculate the log2 as something like x |= x >> 1; x |= x >> 2; x |= x >> 4; x |= x >> 8; x |= x >> 16; return popcount(x-1); but there isn't really much of an advantage to it. lzcnt/bsr are better.