Fix and test format %y

date.h

@@ -4676,7 +4676,7 @@ to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
                 }
                 else if (modified == CharT{})
                 {
-                    y %= 100;
+                    y = std::abs(y) % 100;
                     if (y < 10)
                         os << CharT{'0'};
                     os << y;

test/date_test/format/century.pass.cpp

@@ -26,14 +26,6 @@
 #include <sstream>
 #include <type_traits>
 
-using fortnights = std::chrono::duration<date::weeks::rep,
-                                         std::ratio_multiply<std::ratio<2>,
-                                                             date::weeks::period>>;
-
-using microfortnights = std::chrono::duration<std::int64_t,
-                                              std::ratio_multiply<fortnights::period,
-                                                                  std::micro>>;
-
 int
 main()
 {

test/date_test/format/two_dight_year.pass.cpp

@@ -0,0 +1,121 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date;
+    using namespace std::chrono;
+    std::ostringstream os;
+    os << format("%y", sys_days{jun/1/20001});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/20000});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/19999});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/2001});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/2000});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/1999});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/101});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/100});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/99});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/1});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/0});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-1});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-99});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-100});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-101});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-1999});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-2000});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-2001});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-19999});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-20000});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-20001});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/year::min()});
+    assert(os.str() == "68");
+}