Problem p03708 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define loop(n)                                                                \
  for (int ngtkana_is_genius = 0; ngtkana_is_genius < int(n);                  \
       ngtkana_is_genius++)
#define rep(i, begin, end) for (int i = int(begin); i < int(end); i++)
#define all(v) v.begin(), v.end()
#define rand(l, r) std::uniform_int_distribution<>(l, r)(mt)
#define lint long long
auto cmn = [](auto &a, auto b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
};
auto cmx = [](auto &a, auto b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
};
void debug_impl() { std::cerr << std::endl; }
template <typename Head, typename... Tail>
void debug_impl(Head head, Tail... tail) {
  std::cerr << " " << head;
  debug_impl(tail...);
}
#ifndef STOPIT
#define debug(...)                                                             \
  std::cerr << std::boolalpha << "[" << #__VA_ARGS__ << "]:";                  \
  debug_impl(__VA_ARGS__);                                                     \
  std::cerr << std::noboolalpha;
#else
#define debug 0;
#endif

auto remove_common_header(lint x, lint y) {
  auto mask = std::numeric_limits<lint>::max() >> (__builtin_clzll(x ^ y) - 1);
  return std::make_tuple(x & mask, y & mask, mask);
}

auto ceil2(lint x) {
  if (x == 0 || x == 1)
    return 1LL;
  return (std::numeric_limits<lint>::max() >> __builtin_clzll(x - 1) - 1) + 1;
}

template <typename Container, typename Value = typename Container::value_type,
          std::enable_if_t<!std::is_same<Container, std::string>::value,
                           std::nullptr_t> = nullptr>
std::istream &operator>>(std::istream &is, Container &v) {
  for (auto &x : v) {
    is >> x;
  }
  return is;
}

template <typename Container, typename Value = typename Container::value_type,
          std::enable_if_t<!std::is_same<Container, std::string>::value,
                           std::nullptr_t> = nullptr>
std::ostream &operator<<(std::ostream &os, Container const &v) {
  os << "{";
  for (auto it = v.begin(); it != v.end(); it++) {
    os << (it != v.begin() ? "," : "") << *it;
  }
  return os << "}";
}

int main() {
  std::cin.tie(0);
  std::cin.sync_with_stdio(false);
  lint a, b;
  std::cin >> a >> b;
  lint c;
  std::tie(a, b, c) = remove_common_header(a, b);
  (c /= 2) += 1;
  if (c < b) {
    b = c + ceil2(b + 1 - c) - 1;
  }
  assert(a <= c && c <= b && b < 2 * c);
  auto ret = (c - a) + std::min(c, b - a + 1);
  std::cout << ret << std::endl;
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#define loop(n)                                                                \
  for (int ngtkana_is_genius = 0; ngtkana_is_genius < int(n);                  \
       ngtkana_is_genius++)
#define rep(i, begin, end) for (int i = int(begin); i < int(end); i++)
#define all(v) v.begin(), v.end()
#define rand(l, r) std::uniform_int_distribution<>(l, r)(mt)
#define lint long long
auto cmn = [](auto &a, auto b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
};
auto cmx = [](auto &a, auto b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
};
void debug_impl() { std::cerr << std::endl; }
template <typename Head, typename... Tail>
void debug_impl(Head head, Tail... tail) {
  std::cerr << " " << head;
  debug_impl(tail...);
}
#ifndef STOPIT
#define debug(...)                                                             \
  std::cerr << std::boolalpha << "[" << #__VA_ARGS__ << "]:";                  \
  debug_impl(__VA_ARGS__);                                                     \
  std::cerr << std::noboolalpha;
#else
#define debug 0;
#endif

auto remove_common_header(lint x, lint y) {
  auto mask = std::numeric_limits<lint>::max() >> (__builtin_clzll(x ^ y) - 1);
  return std::make_tuple(x & mask, y & mask, mask);
}

auto ceil2(lint x) {
  if (x == 0 || x == 1)
    return 1LL;
  return (std::numeric_limits<lint>::max() >> __builtin_clzll(x - 1) - 1) + 1;
}

template <typename Container, typename Value = typename Container::value_type,
          std::enable_if_t<!std::is_same<Container, std::string>::value,
                           std::nullptr_t> = nullptr>
std::istream &operator>>(std::istream &is, Container &v) {
  for (auto &x : v) {
    is >> x;
  }
  return is;
}

template <typename Container, typename Value = typename Container::value_type,
          std::enable_if_t<!std::is_same<Container, std::string>::value,
                           std::nullptr_t> = nullptr>
std::ostream &operator<<(std::ostream &os, Container const &v) {
  os << "{";
  for (auto it = v.begin(); it != v.end(); it++) {
    os << (it != v.begin() ? "," : "") << *it;
  }
  return os << "}";
}

int main() {
  std::cin.tie(0);
  std::cin.sync_with_stdio(false);
  lint a, b;
  std::cin >> a >> b;
  if (a == b) {
    std::cout << 1 << std::endl;
    return 0;
  }
  lint c;
  std::tie(a, b, c) = remove_common_header(a, b);
  (c /= 2) += 1;
  if (c < b) {
    b = c + ceil2(b + 1 - c) - 1;
  }
  assert(a <= c && c <= b && b < 2 * c);
  auto ret = (c - a) + std::min(c, b - a + 1);
  std::cout << ret << std::endl;
  return 0;
}