Restart Headers: Add Support for DOUBHEAD Keyword

In particular, implement logic for "datenum" of start point in
addition to elapsed time (in days) and "datenum" of current time
point (start + elapsed).

tests/test_DoubHEAD.cpp

@@ -0,0 +1,91 @@
+/*
+  Copyright 2018 Statoil IT
+
+  This file is part of the Open Porous Media project (OPM).
+
+  OPM is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  OPM is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#define BOOST_TEST_MODULE DoubHEAD_Vector
+
+#include <boost/test/unit_test.hpp>
+
+#include <opm/output/eclipse/DoubHEAD.hpp>
+
+#include <opm/output/eclipse/InteHEAD.hpp>
+
+#include <opm/parser/eclipse/Deck/Deck.hpp>
+#include <opm/parser/eclipse/Parser/Parser.hpp>
+#include <opm/parser/eclipse/Parser/ParseContext.hpp>
+#include <opm/parser/eclipse/EclipseState/Schedule/TimeMap.hpp>
+
+#include <chrono>
+#include <ctime>
+#include <initializer_list>
+#include <numeric>              // partial_sum()
+#include <ratio>
+#include <vector>
+
+namespace {
+    using Day = std::chrono::duration<double,
+        std::ratio_multiply<std::chrono::hours::period, std::ratio<24>>
+    >;
+
+    std::chrono::time_point<std::chrono::system_clock> startSimulation()
+    {
+        // 2015-04-09T00:00:00+0000
+        auto timePoint = std::tm{};
+
+        timePoint.tm_year = 115;     // 2015
+        timePoint.tm_mon  =   4 - 1; // April
+        timePoint.tm_mday =   9;     // 9th
+
+        return std::chrono::system_clock::from_time_t(
+            ::Opm::RestartIO::makeUTCTime(timePoint));
+    }
+
+    std::chrono::duration<double, std::chrono::seconds::period> tstep_123()
+    {
+        return Day{ 123 };
+    }
+
+    Opm::RestartIO::DoubHEAD::TimeStamp
+    makeTStamp(std::chrono::time_point<std::chrono::system_clock>          start,
+               std::chrono::duration<double, std::chrono::seconds::period> elapsed)
+    {
+        return { start, elapsed };
+    }
+} // Anonymous
+
+BOOST_AUTO_TEST_SUITE(Member_Functions)
+
+BOOST_AUTO_TEST_CASE(Time_Stamp)
+{
+    const auto dh = Opm::RestartIO::DoubHEAD{}
+        .timeStamp(makeTStamp(startSimulation(), tstep_123()));
+
+    const auto& v = dh.data();
+
+    // Elapsed time in days.
+    BOOST_CHECK_CLOSE(v[1 - 1], 123.0, 1.0e-10);
+
+    // DateNum(startSimulation()) ==
+    //     floor(365.25 * 2015) + day_of_year(=99)
+    BOOST_CHECK_CLOSE(v[161 - 1], 736077.0, 1.0e-10);
+
+    // Start + elapsed (days)
+    BOOST_CHECK_CLOSE(v[162 - 1], 736200.0, 1.0e-10);
+}
+
+BOOST_AUTO_TEST_SUITE_END()