Ref T308, using an optimized (faster) function for YYYYmmdd string parsing

Ref T309, found that QDateTime::fromString returns a QDateTime object with local timestamp. Using a optimized version returns UTC objects now.

- The bug was found writing a unit test for Ref T308
- Slack: https://swift-project.slack.com/archives/G7GD2UP9C/p1534848725000100

tests/blackmisc/teststringutils.cpp

@@ -18,6 +18,7 @@
 #include "blackmisc/stringutils.h"
 
 #include <QTest>
+#include <QTime>
 
 using namespace BlackMisc;
 
@@ -48,7 +49,7 @@ namespace BlackMiscTest
 
     void CTestStringUtils::testSplit()
     {
-        QString s = "line one\nline two\r\nline three\n";
+        const QString s = "line one\nline two\r\nline three\n";
         QStringList lines = splitLines(s);
         QVERIFY2(lines.size() == 3, "Test split string into lines: correct number of lines");
         QVERIFY2(lines[0] == "line one", "Test split string into lines: correct first line");
@@ -56,6 +57,76 @@ namespace BlackMiscTest
         QVERIFY2(lines[2] == "line three", "Test split string into lines: correct third line");
     }
 
+    void CTestStringUtils::testTimestampParsing()
+    {
+        const QStringList dts(
+        {
+            "2018-01-01 11:11:11",
+            "2012-05-09 03:04:05.777",
+            "2012-05-09 00:00:00.000",
+            "2015-12-31 03:04:05",
+            "1999-12-31 23:59:59.999",
+            "1975-01-01 14:13:17",
+            "1982-05-09 03:01:05.123",
+            "2000-05-02 00:04:00.000",
+            "2002-12-31 03:34:33",
+            "1992-11-01 21:59:29.999"
+        });
+
+        const int size = QString("yyyyMMddHHmmss").size();
+        for (const QString &dt : dts)
+        {
+            const QString c = removeDateTimeSeparators(dt);
+            const QDateTime dt1 = parseDateTimeStringOptimized(c);
+            const QDateTime dt2 = (c.length() == size) ?
+                                  fromStringUtc(c, "yyyyMMddHHmmss") :
+                                  fromStringUtc(c, "yyyyMMddHHmmsszzz");
+            QDateTime dt3 = (c.length() == size) ?
+                            QDateTime::fromString(c, "yyyyMMddHHmmss") :
+                            QDateTime::fromString(c, "yyyyMMddHHmmsszzz");
+            dt3.setUtcOffset(0);
+
+            const qint64 ms1 = dt1.toMSecsSinceEpoch();
+            const qint64 ms2 = dt2.toMSecsSinceEpoch();
+            const qint64 delta = ms1 - ms2;
+
+            QVERIFY2(dt1 == dt2, "Expect same results of QDateTime");
+            QVERIFY2(dt1 == dt3, "Expect same results of QDateTime");
+            QVERIFY2(delta == 0, "Expect same results timestamp");
+        }
+
+        // performance
+        int constexpr Loops = 10000;
+        QTime time;
+        time.start();
+        for (int i = 0; i < Loops; i++)
+        {
+            for (const QString &dt : dts)
+            {
+                const QString c = removeDateTimeSeparators(dt);
+                const QDateTime dateTime = parseDateTimeStringOptimized(c);
+                parseDateTimeStringOptimized(c);
+                Q_UNUSED(dateTime); // avoid optimizing out of call
+            }
+        }
+        const int elapsedOptimized = time.restart();
+
+        for (int i = 0; i < Loops; i++)
+        {
+            for (const QString &dt : dts)
+            {
+                const QString c = removeDateTimeSeparators(dt);
+                const QDateTime dateTime = (c.length() == size) ?
+                                           fromStringUtc(c, "yyyyMMddHHmmss") :
+                                           fromStringUtc(c, "yyyyMMddHHmmsszzz");
+                Q_UNUSED(dateTime); // avoid optimizing out of call
+            }
+        }
+        const int elapsedQt = time.restart();
+
+        qDebug() << "Parsing date/time, optimized" << elapsedOptimized << "vs. QDateTime: " << elapsedQt;
+        QVERIFY2(elapsedOptimized < elapsedQt, "Expect optimized being faster as QDateTim::fromString");
+    }
 }
 
 //! \endcond

tests/blackmisc/teststringutils.h

@@ -21,7 +21,6 @@
 
 namespace BlackMiscTest
 {
-
     //! Testing string utilities
     class CTestStringUtils : public QObject
     {
@@ -36,8 +35,8 @@ namespace BlackMiscTest
         void testContains();
         void testIndexOf();
         void testSplit();
+        void testTimestampParsing();
     };
-
 }
 
 //! \endcond