[libc++][format] Fixes times before epoch.

[Mordante]

Summary

The number of days should be rounded down, for both positive and
negative times since epoch. The original code truncated, which is
correct for positive values, but wrong for negative values.

Depends on D138826

[Mordante]

Rebased to test CI.

[Mordante]

Retrigger CI.

[h-vetinari]

35bit -> 32bit?

[Mordante]

libcxx/test/std/time/time.syn/formatter.file_time.pass.cpp

53

@h-vetinari you mean here? This should be 35. I probably should add a link to http://eel.is/c++draft/time.syn.

// convenience typedefs
using nanoseconds  = duration<signed integer type of at least 64 bits, nano>;
using microseconds = duration<signed integer type of at least 55 bits, micro>;
using milliseconds = duration<signed integer type of at least 45 bits, milli>;
using seconds      = duration<signed integer type of at least 35 bits>;
using minutes      = duration<signed integer type of at least 29 bits, ratio<  60>>;
using hours        = duration<signed integer type of at least 23 bits, ratio<3600>>;

[h-vetinari]

libcxx/test/std/time/time.syn/formatter.file_time.pass.cpp

53

My mistake, sorry. I thought 32 vs. 35 might be a numpad-off-by-one-row error. "35 bit minimum" sounded like "smallest/oldest representable", but from the standard you cited it, it's not the minimum as in representable time, but the minimum as in "we need at least 35 bits"...

Sorry for the noise.

[Mordante]

libcxx/test/std/time/time.syn/formatter.file_time.pass.cpp

53

No problem, I appreciate your feedback!

[ldionne]

libcxx/test/std/time/time.syn/formatter.file_time.pass.cpp

53

I agree, let's add a link to the wording.

libcxx/include/__chrono/convert_to_tm.h

__result.tm_yday =
        static_cast<chrono::sys_days>(chrono::year_month_day{__date.year(), chrono::January, chrono::day{1}}))
           .count();
 
   return __result;
 }
 
 template <class _Tm, class _Duration>
 _LIBCPP_HIDE_FROM_ABI _Tm __convert_to_tm(const chrono::sys_time<_Duration> __tp) {
-  chrono::sys_days __days = chrono::time_point_cast<chrono::days>(__tp);
+  chrono::sys_days __days = chrono::floor<chrono::days>(__tp);
   chrono::year_month_day __ymd{__days};
 
   _Tm __result = std::__convert_to_tm<_Tm>(chrono::year_month_day{__ymd}, chrono::weekday{__days});
 
   uint64_t __sec =
       chrono::duration_cast<chrono::seconds>(__tp - chrono::time_point_cast<chrono::seconds>(__days)).count();
   __sec %= 24 * 3600;
   __result.tm_hour = __sec / 3600;

libcxx/test/std/time/time.syn/formatter.file_time.pass.cpp

 
 template <class CharT>
 static void test_no_chrono_specs() {
   using namespace std::literals::chrono_literals;
 
   std::locale::global(std::locale(LOCALE_fr_FR_UTF_8));
 
   // Non localized output
+
+  check(SV("1425-08-04 22:06:56"), SV("{}"), file_seconds(-17'179'869'184s)); // 35 bit minimum
+  check(SV("1901-12-13 20:45:52"), SV("{}"), file_seconds(-2'147'483'648s));
+
+  check(SV("1969-12-31 00:00:00"), SV("{}"), file_seconds(-24h));
+  check(SV("1969-12-31 06:00:00"), SV("{}"), file_seconds(-18h));
+  check(SV("1969-12-31 12:00:00"), SV("{}"), file_seconds(-12h));
+  check(SV("1969-12-31 18:00:00"), SV("{}"), file_seconds(-6h));
+  check(SV("1969-12-31 23:59:59"), SV("{}"), file_seconds(-1s));
+
   check(SV("1970-01-01 00:00:00"), SV("{}"), file_seconds(0s));
   check(SV("2000-01-01 00:00:00"), SV("{}"), file_seconds(946'684'800s));
   check(SV("2000-01-01 01:02:03"), SV("{}"), file_seconds(946'688'523s));
 
+  check(SV("2038-01-19 03:14:07"), SV("{}"), file_seconds(2'147'483'647s));
+  check(SV("2514-05-30 01:53:03"), SV("{}"), file_seconds(17'179'869'183s)); // 35 bit maximum
+
   check(SV("2000-01-01 01:02:03.123"), SV("{}"), file_time<std::chrono::milliseconds>(946'688'523'123ms));
 
   std::locale::global(std::locale::classic());
 }
 
 template <class CharT>
 static void test_valid_values_year() {
   using namespace std::literals::chrono_literals;

libcxx/test/std/time/time.syn/formatter.local_time.pass.cpp

 
 template <class CharT>
 static void test_no_chrono_specs() {
   using namespace std::literals::chrono_literals;
 
   std::locale::global(std::locale(LOCALE_fr_FR_UTF_8));
 
   // Non localized output
+
+  check(SV("1425-08-04 22:06:56"), SV("{}"), std::chrono::local_seconds(-17'179'869'184s)); // 35 bit minimum
+  check(SV("1901-12-13 20:45:52"), SV("{}"), std::chrono::local_seconds(-2'147'483'648s));
+
+  check(SV("1969-12-31 00:00:00"), SV("{}"), std::chrono::local_seconds(-24h));
+  check(SV("1969-12-31 06:00:00"), SV("{}"), std::chrono::local_seconds(-18h));
+  check(SV("1969-12-31 12:00:00"), SV("{}"), std::chrono::local_seconds(-12h));
+  check(SV("1969-12-31 18:00:00"), SV("{}"), std::chrono::local_seconds(-6h));
+  check(SV("1969-12-31 23:59:59"), SV("{}"), std::chrono::local_seconds(-1s));
+
   check(SV("1970-01-01 00:00:00"), SV("{}"), std::chrono::local_seconds(0s));
   check(SV("2000-01-01 00:00:00"), SV("{}"), std::chrono::local_seconds(946'684'800s));
   check(SV("2000-01-01 01:02:03"), SV("{}"), std::chrono::local_seconds(946'688'523s));
 
+  check(SV("2038-01-19 03:14:07"), SV("{}"), std::chrono::local_seconds(2'147'483'647s));
+  check(SV("2514-05-30 01:53:03"), SV("{}"), std::chrono::local_seconds(17'179'869'183s)); // 35 bit maximum
+
   check(SV("2000-01-01 01:02:03.123"), SV("{}"), std::chrono::local_time<std::chrono::milliseconds>(946'688'523'123ms));
 
   std::locale::global(std::locale::classic());
 }
 
 template <class CharT>
 static void test_valid_values_year() {
   using namespace std::literals::chrono_literals;

libcxx/test/std/time/time.syn/formatter.sys_time.pass.cpp

 
 template <class CharT>
 static void test_no_chrono_specs() {
   using namespace std::literals::chrono_literals;
 
   std::locale::global(std::locale(LOCALE_fr_FR_UTF_8));
 
   // Non localized output
+
+  check(SV("1425-08-04 22:06:56"), SV("{}"), std::chrono::sys_seconds(-17'179'869'184s)); // 35 bit minimum
+  check(SV("1901-12-13 20:45:52"), SV("{}"), std::chrono::sys_seconds(-2'147'483'648s));
+
+  check(SV("1969-12-31 00:00:00"), SV("{}"), std::chrono::sys_seconds(-24h));
+  check(SV("1969-12-31 06:00:00"), SV("{}"), std::chrono::sys_seconds(-18h));
+  check(SV("1969-12-31 12:00:00"), SV("{}"), std::chrono::sys_seconds(-12h));
+  check(SV("1969-12-31 18:00:00"), SV("{}"), std::chrono::sys_seconds(-6h));
+  check(SV("1969-12-31 23:59:59"), SV("{}"), std::chrono::sys_seconds(-1s));
+
   check(SV("1970-01-01 00:00:00"), SV("{}"), std::chrono::sys_seconds(0s));
   check(SV("2000-01-01 00:00:00"), SV("{}"), std::chrono::sys_seconds(946'684'800s));
   check(SV("2000-01-01 01:02:03"), SV("{}"), std::chrono::sys_seconds(946'688'523s));
 
+  check(SV("2038-01-19 03:14:07"), SV("{}"), std::chrono::sys_seconds(2'147'483'647s));
+  check(SV("2514-05-30 01:53:03"), SV("{}"), std::chrono::sys_seconds(17'179'869'183s)); // 35 bit maximum
+
   check(SV("2000-01-01 01:02:03.123"), SV("{}"), std::chrono::sys_time<std::chrono::milliseconds>(946'688'523'123ms));
 
   std::locale::global(std::locale::classic());
 }
 
 template <class CharT>
 static void test_valid_values_year() {
   using namespace std::literals::chrono_literals;