Function Log2Floor64

tensorflow/core/lib/strings/ordered_code.cc:414–416

Returns floor(lg(n)). Returns -1 if n == 0.

#if defined(__GNUC__)
// Returns floor(lg(n)).  Returns -1 if n == 0.
static int Log2Floor64(uint64 n) {
  return n == 0 ? -1 : 63 ^ __builtin_clzll(n);
}
#else
// Portable slow version
static int Log2Floor32_Portable(uint32 n) {