#include <time.h>
#include <stdio.h>
#include <stdint.h>

int Log2FloorBASE(uint32_t n) {
  if (n == 0)
    return -1;
  int log = 0;
  uint32_t value = n;
  for (int i = 4; i >= 0; --i) {
    int shift = (1 << i);
    uint32_t x = value >> shift;
    if (x != 0) {
      value = x;
      log += shift;
    }
  }
  return log;
}

int Log2FloorNEW(uint64_t n) {
 if (!n) return -1;
 int log = 0;
 for (int i = 5; i >= 0; ++i) {
   int shift = 1 << i;
   if (n >> shift) {
     log += shift;
     if (!(n >>= shift)) break;
   }
 }
 return log;
}


int main() {
  time_t t = time(NULL);
  printf("base: %d\n", Log2FloorBASE(128));
  printf("  took: %ld seconds\n", time(NULL) - t);

  t = time(NULL);
  printf("new: %d\n", Log2FloorNEW(128));
  printf("  took: %ld seconds\n", time(NULL) - t);

  return 0;
}


$ g++ -o test test.cc && ./test
base: 7
  took: 0 seconds
new: 7
  took: 9 seconds