Function log2_pot

dependence/eigen-3.4.0/bench/benchmark-blocking-sizes.cpp:76–80

};

uint8_t log2_pot(size_t x) {
  size_t l = 0;
  while (x >>= 1) l++;
  return l;
}

// Convert between size tripes and a compact form fitting in 12 bits
// where each size, which must be a POT, is encoded as its log2, on 4 bits