1 files changed, 94 insertions, 0 deletions
diff --git a/test/std/utilities/time/time.cal/time.cal.ymd/time.cal.ymd.members/op.sys_days.pass.cpp b/test/std/utilities/time/time.cal/time.cal.ymd/time.cal.ymd.members/op.sys_days.pass.cpp
new file mode 100644
index 0000000000000..4e263bcccb6b0
--- /dev/null
+++ b/test/std/utilities/time/time.cal/time.cal.ymd/time.cal.ymd.members/op.sys_days.pass.cpp
@@ -0,0 +1,94 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <chrono>
+// class year_month_day;
+
+// constexpr operator sys_days() const noexcept;
+//
+// Returns: If ok(), returns a sys_days holding a count of days from the
+//   sys_days epoch to *this (a negative value if *this represents a date
+//   prior to the sys_days epoch). Otherwise, if y_.ok() && m_.ok() is true,
+//   returns a sys_days which is offset from sys_days{y_/m_/last} by the
+//   number of days d_ is offset from sys_days{y_/m_/last}.day(). Otherwise
+//   the value returned is unspecified.
+//
+// Remarks: A sys_days in the range [days{-12687428}, days{11248737}] which
+//   is converted to a year_month_day shall have the same value when
+//   converted back to a sys_days.
+//
+// [Example:
+//   static_assert(year_month_day{sys_days{2017y/January/0}}  == 2016y/December/31);
+//   static_assert(year_month_day{sys_days{2017y/January/31}} == 2017y/January/31);
+//   static_assert(year_month_day{sys_days{2017y/January/32}} == 2017y/February/1);
+// —end example]
+
+#include <chrono>
+#include <type_traits>
+#include <cassert>
+
+#include "test_macros.h"
+
+void RunTheExample()
+{
+    using namespace std::chrono;
+
+    static_assert(year_month_day{sys_days{year{2017}/January/0}}  == year{2016}/December/31);
+    static_assert(year_month_day{sys_days{year{2017}/January/31}} == year{2017}/January/31);
+    static_assert(year_month_day{sys_days{year{2017}/January/32}} == year{2017}/February/1);  
+}
+
+int main()
+{
+    using year           = std::chrono::year;
+    using month          = std::chrono::month;
+    using day            = std::chrono::day;
+    using sys_days       = std::chrono::sys_days;
+    using days           = std::chrono::days;
+    using year_month_day = std::chrono::year_month_day;
+
+    ASSERT_NOEXCEPT(sys_days(std::declval<year_month_day>()));
+    RunTheExample();
+
+    {
+    constexpr year_month_day ymd{year{1970}, month{1}, day{1}};
+    constexpr sys_days sd{ymd};
+
+    static_assert( sd.time_since_epoch() == days{0}, "");
+    static_assert( year_month_day{sd} == ymd, ""); // and back
+    }
+
+    {
+    constexpr year_month_day ymd{year{2000}, month{2}, day{2}};
+    constexpr sys_days sd{ymd};
+
+    static_assert( sd.time_since_epoch() == days{10957+32}, "");
+    static_assert( year_month_day{sd} == ymd, ""); // and back
+    }
+
+//  There's one more leap day between 1/1/40 and 1/1/70
+//  when compared to 1/1/70 -> 1/1/2000
+    {
+    constexpr year_month_day ymd{year{1940}, month{1}, day{2}};
+    constexpr sys_days sd{ymd};
+
+    static_assert( sd.time_since_epoch() == days{-10957}, "");
+    static_assert( year_month_day{sd} == ymd, ""); // and back
+    }
+
+    {
+    year_month_day ymd{year{1939}, month{11}, day{29}};
+    sys_days sd{ymd};
+
+    assert( sd.time_since_epoch() == days{-(10957+34)});
+    assert( year_month_day{sd} == ymd); // and back
+    }
+
+}