[libcxx-commits] [libcxx] a4814bd - [libc++][chrono] Fixes formatter duration.

[Mark de Wever via libcxx-commits]

Author: Mark de Wever
Date: 2023-07-15T12:02:03+02:00
New Revision: a4814bdc5371c480b66f655b4a5a68b7ed07000a

URL: https://github.com/llvm/llvm-project/commit/a4814bdc5371c480b66f655b4a5a68b7ed07000a
DIFF: https://github.com/llvm/llvm-project/commit/a4814bdc5371c480b66f655b4a5a68b7ed07000a.diff

LOG: [libc++][chrono] Fixes formatter duration.

@EricWF spotted this issue in the post-commit review comments of
D134742. However the suggestion to just use chrono calculations can
result in similar issues when using small fractional seconds.

Reviewed By: EricWF, #libc

Differential Revision: https://reviews.llvm.org/D138826

Added: 
    

Modified: 
    libcxx/include/__chrono/convert_to_tm.h
    libcxx/test/std/time/time.syn/formatter.duration.pass.cpp

Removed: 
    


################################################################################
diff  --git a/libcxx/include/__chrono/convert_to_tm.h b/libcxx/include/__chrono/convert_to_tm.h
index f4dcddece74cd7..cc97bfd005a1b6 100644
--- a/libcxx/include/__chrono/convert_to_tm.h
+++ b/libcxx/include/__chrono/convert_to_tm.h
@@ -31,6 +31,7 @@
 #include <__config>
 #include <__format/format_error.h>
 #include <__memory/addressof.h>
+#include <__type_traits/is_convertible.h>
 #include <cstdint>
 #include <ctime>
 #include <limits>
@@ -116,12 +117,23 @@ _LIBCPP_HIDE_FROM_ABI _Tm __convert_to_tm(const _ChronoT& __value) {
     //   ...  However, if a flag refers to a "time of day" (e.g. %H, %I, %p,
     //   etc.), then a specialization of duration is interpreted as the time of
     //   day elapsed since midnight.
-    uint64_t __sec = chrono::duration_cast<chrono::seconds>(__value).count();
-    __sec %= 24 * 3600;
-    __result.tm_hour = __sec / 3600;
-    __sec %= 3600;
-    __result.tm_min = __sec / 60;
-    __result.tm_sec = __sec % 60;
+
+    // Not all values can be converted to hours, it may run into ratio
+    // conversion errors. In that case the conversion to seconds works.
+    if constexpr (is_convertible_v<_ChronoT, chrono::hours>) {
+      auto __hour      = chrono::floor<chrono::hours>(__value);
+      auto __sec       = chrono::duration_cast<chrono::seconds>(__value - __hour);
+      __result.tm_hour = __hour.count() % 24;
+      __result.tm_min  = __sec.count() / 60;
+      __result.tm_sec  = __sec.count() % 60;
+    } else {
+      uint64_t __sec = chrono::duration_cast<chrono::seconds>(__value).count();
+      __sec %= 24 * 3600;
+      __result.tm_hour = __sec / 3600;
+      __sec %= 3600;
+      __result.tm_min = __sec / 60;
+      __result.tm_sec = __sec % 60;
+    }
   } else if constexpr (same_as<_ChronoT, chrono::day>)
     __result.tm_mday = static_cast<unsigned>(__value);
   else if constexpr (same_as<_ChronoT, chrono::month>)

diff  --git a/libcxx/test/std/time/time.syn/formatter.duration.pass.cpp b/libcxx/test/std/time/time.syn/formatter.duration.pass.cpp
index c3fd0f2315a453..0ba8abdb87bb23 100644
--- a/libcxx/test/std/time/time.syn/formatter.duration.pass.cpp
+++ b/libcxx/test/std/time/time.syn/formatter.duration.pass.cpp
@@ -1152,6 +1152,22 @@ static void test() {
   check_exception("End of input while parsing the modifier E", SV("{:%E"), 0ms);
   check_exception("End of input while parsing the modifier O", SV("{:%O"), 0ms);
 
+  // Make sure the the required values work, based on their minimum number of required bits per [time.syn].
+  check(SV("23:47:16.854775807"),
+        SV("{:%T}"),
+        std::chrono::nanoseconds{0x7fff'ffff'ffff'ffffll}); // 64 bit signed value max
+  check(SV("23:35:09.481983"),
+        SV("{:%T}"),
+        std::chrono::microseconds{0x003f'ffff'ffff'ffffll});                                 // 55 bit signed value max
+  check(SV("06:20:44.415"), SV("{:%T}"), std::chrono::milliseconds{0x0000'fff'ffff'ffffll}); // 45 bit signed value max
+  check(SV("01:53:03"), SV("{:%T}"), std::chrono::seconds{0x0000'0003'ffff'ffffll});         // 35 bit signed value max
+  check(SV("12:15:00"), SV("{:%T}"), std::chrono::minutes{0x0fff'ffff});                     // 29 bit signed value max
+  check(SV("15:00:00"), SV("{:%T}"), std::chrono::hours{0x003f'ffff});                       // 23 bit signed value max
+  check(SV("00:00:00"), SV("{:%T}"), std::chrono::days{0x0ff'ffff});                         // 25 bit signed value max
+  check(SV("00:00:00"), SV("{:%T}"), std::chrono::weeks{0x003f'ffff});                       // 22 bit signed value max
+  check(SV("21:11:42"), SV("{:%T}"), std::chrono::months{0x0007'ffff});                      // 20 bit signed value max
+  check(SV("05:42:00"), SV("{:%T}"), std::chrono::years{0xffff});                            // 17 bit signed value max
+
   // Precision not allowed
   check_exception("Expected '%' or '}' in the chrono format-string", SV("{:.3}"), 0ms);
 }