Switch internal year calculations to long long

include/fmt/chrono.h

@@ -1450,8 +1450,8 @@ template <typename OutputIt, typename Char> class tm_writer {
                "tm_mon not in range [0, 11]");
     return to_unsigned(tm_.tm_mon);
   }
-  auto tm_year() const noexcept -> int {
-    return 1900 + tm_.tm_year;
+  auto tm_year() const noexcept -> long long {
+    return 1900ll + static_cast<long long>(tm_.tm_year);
   }
   auto tm_wday() const noexcept -> unsigned {
     FMT_ASSERT(tm_.tm_wday >= 0 && tm_.tm_wday <= 6,
@@ -1469,11 +1469,11 @@ template <typename OutputIt, typename Char> class tm_writer {
     return hour == 0 ? 12 : hour;
   }
 
-  FMT_CONSTEXPR const Char* tm_day_of_week() const noexcept {
+  FMT_CONSTEXPR const Char* tm_day_of_week_name() const noexcept {
     auto wday = tm_wday();
     return (wday >= 0 && wday <= 6) ? day_of_week[wday] : invalid;
   }
-  FMT_CONSTEXPR const Char* tm_month() const noexcept {
+  FMT_CONSTEXPR const Char* tm_mon_name() const noexcept {
     auto mon = tm_mon();
     return (mon >= 0 && mon <= 11) ? month[mon] : invalid;
   }
@@ -1482,21 +1482,20 @@ template <typename OutputIt, typename Char> class tm_writer {
   // do if the year is negative or exceeds 9999. Use the convention that %C
   // concatenated with %y yields the same output as %Y, and that %Y contains at
   // least 4 characters, with more only if necessary.
-  auto split_year_lower(int year) const noexcept -> unsigned {
+  auto split_year_lower(const long long year) const noexcept -> unsigned {
     auto l = year % 100;
     if (l < 0) l = -l;  // l in [0, 99]
-    return to_unsigned(l);
+    return static_cast<unsigned>(l);
   }
 
   // Algorithm:
   // https://en.wikipedia.org/wiki/ISO_week_date#Calculating_the_week_number_from_a_month_and_day_of_the_month_or_ordinal_date
-  auto iso_year_weeks(const int year) const noexcept -> unsigned {
-    const long long curr_year = year;
+  auto iso_year_weeks(const long long curr_year) const noexcept -> unsigned {
     const long long prev_year = curr_year - 1;
-    const int curr_p = static_cast<int>(
+    const unsigned curr_p = static_cast<unsigned>(
         (curr_year + curr_year / 4 - curr_year / 100 + curr_year / 400) %
         days_per_week);
-    const int prev_p = static_cast<int>(
+    const unsigned prev_p = static_cast<unsigned>(
         (prev_year + prev_year / 4 - prev_year / 100 + prev_year / 400) %
         days_per_week);
     return 52u + ((curr_p == 4 || prev_p == 3) ? 1u : 0u);
@@ -1506,7 +1505,7 @@ template <typename OutputIt, typename Char> class tm_writer {
     return (tm_yday + 11 - (tm_wday == 0 ? days_per_week : tm_wday)) /
            days_per_week;
   }
-  auto tm_iso_week_year() const noexcept -> int {
+  auto tm_iso_week_year() const noexcept -> long long {
     const auto year = tm_year();
     const unsigned w = iso_week_num(tm_yday(), tm_wday());
     if (w < 1) return year - 1;
@@ -1528,24 +1527,23 @@ template <typename OutputIt, typename Char> class tm_writer {
     *out_++ = *d;
   }
 
-  void write_year_extended(int year) {
+  void write_year_extended(long long year) {
     // At least 4 characters.
     int width = 4;
     if (year < 0) {
       *out_++ = '-';
       year = 0 - year;
       --width;
     }
-    uint32_or_64_or_128_t<int> n =
-        to_unsigned(to_nonnegative_int(year, max_value<int>()));
+    uint32_or_64_or_128_t<long long> n = to_unsigned(year);
     const int num_digits = count_digits(n);
     if (width > num_digits) out_ = std::fill_n(out_, width - num_digits, '0');
     out_ = format_decimal<Char>(out_, n, num_digits).end;
   }
-  void write_year(int year) {
+  void write_year(long long year) {
     if (year >= 0 && year < 10000) {
-      write2(to_unsigned(year / 100));
-      write2(to_unsigned(year % 100));
+      write2(static_cast<unsigned>(year / 100));
+      write2(static_cast<unsigned>(year % 100));
     } else
       write_year_extended(year);
   }
@@ -1569,13 +1567,13 @@ template <typename OutputIt, typename Char> class tm_writer {
 
   void on_abbr_weekday() {
     if (is_classic_)
-      out_ = write(out_, basic_string_view<Char>(tm_day_of_week(), 3));
+      out_ = write(out_, basic_string_view<Char>(tm_day_of_week_name(), 3));
     else
       format_localized('a');
   }
   void on_full_weekday() {
     if (is_classic_)
-      out_ = write(out_, tm_day_of_week());
+      out_ = write(out_, tm_day_of_week_name());
     else
       format_localized('A');
   }
@@ -1591,13 +1589,13 @@ template <typename OutputIt, typename Char> class tm_writer {
 
   void on_abbr_month() {
     if (is_classic_)
-      out_ = write(out_, basic_string_view<Char>(tm_month(), 3));
+      out_ = write(out_, basic_string_view<Char>(tm_mon_name(), 3));
     else
       format_localized('b');
   }
   void on_full_month() {
     if (is_classic_)
-      out_ = write(out_, tm_month());
+      out_ = write(out_, tm_mon_name());
     else
       format_localized('B');
   }
@@ -1651,7 +1649,8 @@ template <typename OutputIt, typename Char> class tm_writer {
       write_year_extended(year);
       year = 0;
     }
-    write_digit2_separated(buf + 2, year % 100, tm_mon() + 1, tm_mday(), '-');
+    write_digit2_separated(buf + 2, static_cast<unsigned>(year % 100),
+                           tm_mon() + 1, tm_mday(), '-');
     out_ = copy_str<Char>(std::begin(buf) + offset, std::end(buf), out_);
   }
 
@@ -1677,7 +1676,7 @@ template <typename OutputIt, typename Char> class tm_writer {
       *out_++ = '-';
       *out_++ = '0';
     } else if (upper >= 0 && upper < 100) {
-      write2(to_unsigned(upper));
+      write2(static_cast<unsigned>(upper));
     } else {
       out_ = write<Char>(out_, upper);
     }

test/chrono-test.cc

@@ -96,6 +96,13 @@ TEST(chrono_test, format_tm) {
   EXPECT_EQ(fmt::format("{:%Y}", tm), "0027");
   EXPECT_EQ(fmt::format("{:%C%y}", tm), "0027");
 
+  // Overflow year
+  tm.tm_year = 2147483647;
+  EXPECT_EQ(fmt::format("{:%Y}", tm), "2147485547");
+
+  tm.tm_year = -2147483648;
+  EXPECT_EQ(fmt::format("{:%Y}", tm), "-2147481748");
+
   // for week on the year
   // https://www.cl.cam.ac.uk/~mgk25/iso-time.html
   std::vector<std::tm> tm_list = {