fix UB in str2int

include/ProgramOptions.hxx

@@ -628,21 +628,33 @@ namespace po {
  template<typename T, typename forward_iterator_t>
  parsing_report<T> str2int(forward_iterator_t first, forward_iterator_t last) {
  static_assert(std::numeric_limits<T>::is_integer && std::numeric_limits<T>::is_signed, "str2uint only supports signed integral types");
+ static_assert(std::numeric_limits<T>::min() == -std::numeric_limits<T>::max() - 1, "type insufficient; doesn't employ two's complement");
+
+ using unsigned_t = typename std::make_unsigned<T>::type;
+ static_assert(std::numeric_limits<unsigned_t>::max() > std::numeric_limits<T>::max(), "type insufficient");
 
  for(; first != last && std::isspace(*first); ++first);
  const bool neg = expect(first, last, '-');
  if(!neg)
  expect(first, last, '+');
  if(first == last || !is_digit(*first))
  return error_code::conversion_error;
- using unsigned_t = typename std::make_unsigned<T>::type;
  const auto report = str2uint<unsigned_t>(first, last);
  if(!report)
  return report.error;
- unsigned_t max = neg ? static_cast<unsigned_t>(-std::numeric_limits<T>::min()) : static_cast<unsigned_t>(std::numeric_limits<T>::max());
- if(report > max)
- return error_code::out_of_range;
- return neg ? -static_cast<T>(report) : static_cast<T>(report);
+ if(neg) {
+ constexpr unsigned_t neg_max = static_cast<unsigned_t>(std::numeric_limits<T>::max()) + 1;
+ if(report > neg_max)
+ return error_code::out_of_range;
+ else if(report == neg_max)
+ return std::numeric_limits<T>::min();
+ else
+ return -static_cast<T>(report);
+ } else {
+ if(report > static_cast<unsigned_t>(std::numeric_limits<T>::max()))
+ return error_code::out_of_range;
+ return static_cast<T>(report);
+ }
  }
  template<typename T>
  parsing_report<T> str2int(std::string const& str) {