code.c

int most_significant_bit_position(size_t value) {
  // int count = 0;
  // while (value != 0) {
  //   value >>= 1;
  //   count++;
  // }
  // return count;
  assert(value > 0);
  value = (uint64_t) value;
  int count = 0;
  printf("----\n");
  printf("value: %zx, count: %d\n", value, count);
  if ((value & 0x00000000FFFFFFFF) == 0) {
    count += 32;
    value = value >> 32;
  }
  if ((value & 0x000000000000FFFF) == 0) {
    count += 16;
    value = value >> 16;
  }
  if ((value & 0x00000000000000FF) == 0) {
    count += 8;
    value = value >> 8;
  }
  if ((value & 0x000000000000000F) == 0) {
    count += 4;
    value = value >> 4;
  }
  if ((value & 0x0000000000000003) == 0) {
    count += 2;
    value = value >> 2;
  }
  if ((value & 0x0000000000000001) == 0) {
    count += 1;
  }
  printf("value: %zx, count: %d\n", value, count);
  printf("returning: 64-count: %d\n", 64-count);
  return 64 - count;
}