Resolves: tdf#100452 class Date full (BCE,CE) proleptic Gregorian calendar

... implementing signed years with year 0 gap.
Date(31,12,-1) last day BCE
Date(1,1,1) first day CE

New class Date member functions:
* AddYears(sal_Int16) to be used instead of
aDate.SetYear(aDate.GetYear()+sal_Int16) to handle year 0 gap.
* convenience GetNextYear() to be used insted of GetYear()+1
* convenience GetPrevYear() to be used insted of GetYear()-1
* AddMonths(sal_Int32)
* operator=(const css::util::Date&)

New class DateTime member functions:
* operator=(const css::util::DateTime&)

Made some conversion ctors explicit, specifically Date(sal_Int32)

Adapted hopefully all places that used a sal_uInt16 year to use
sal_Int16 where appropriate.

Eliminated some quirks in date handling found on the fly.

Added era handling to i18npool icu calendar setting interface, which
missing was responsible for 0001-01-01 entered in Calc being set as
-0001-01-01, hence subtracting one day resulted in -0002-12-31.

Change-Id: I77b39fba9599ebd5067d7864f6c9ebe01f6f578f
Reviewed-on: https://gerrit.libreoffice.org/27049
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins <ci@libreoffice.org>

49 files changed, 523 insertions, 232 deletions

diff --git a/basic/source/runtime/methods.cxx b/basic/source/runtime/methods.cxx
index 296af1514bcd..2abca341ca68 100644
--- a/basic/source/runtime/methods.cxx
+++ b/basic/source/runtime/methods.cxx
@@ -4858,7 +4858,7 @@ sal_Int16 implGetDateYear( double aDate )
     long nDays = (long) aDate;
     nDays -= 2; // standardize: 1.1.1900 => 0.0
     aRefDate += nDays;
-    sal_Int16 nRet = (sal_Int16)( aRefDate.GetYear() );
+    sal_Int16 nRet = aRefDate.GetYear();
     return nRet;
 }
 
@@ -4917,7 +4917,7 @@ bool implDateSerial( sal_Int16 nYear, sal_Int16 nMonth, sal_Int16 nDay, double&
             {
                 nYearAdj = ( ( nMonth -12 ) / 12 );
             }
-            aCurDate.SetYear( aCurDate.GetYear() + nYearAdj );
+            aCurDate.AddYears( nYearAdj );
         }
 
         // adjust day value,
diff --git a/chart2/source/tools/NumberFormatterWrapper.cxx b/chart2/source/tools/NumberFormatterWrapper.cxx
index 52c6a5250a55..1151aa4aeaab 100644
--- a/chart2/source/tools/NumberFormatterWrapper.cxx
+++ b/chart2/source/tools/NumberFormatterWrapper.cxx
@@ -98,7 +98,8 @@ OUString NumberFormatterWrapper::getFormattedString( sal_Int32 nNumberFormatKey,
         return aText;
     }
     // i99104 handle null date correctly
-    sal_uInt16 nYear = 1899,nDay = 30,nMonth = 12;
+    sal_Int16 nYear = 1899;
+    sal_uInt16 nDay = 30,nMonth = 12;
     if ( m_aNullDate.hasValue() )
     {
         Date* pDate = m_pNumberFormatter->GetNullDate();
diff --git a/chart2/source/view/axes/DateHelper.cxx b/chart2/source/view/axes/DateHelper.cxx
index d8c872711c51..42a77cd045ec 100644
--- a/chart2/source/view/axes/DateHelper.cxx
+++ b/chart2/source/view/axes/DateHelper.cxx
@@ -37,27 +37,17 @@ bool DateHelper::IsInSameMonth( const Date& rD1, const Date& rD2 )
         && (rD1.GetMonth() == rD2.GetMonth());
 }
 
-Date DateHelper::GetDateSomeMonthsAway( const Date& rD, long nMonthDistance )
+Date DateHelper::GetDateSomeMonthsAway( const Date& rD, sal_Int32 nMonthDistance )
 {
     Date aRet(rD);
-    long nMonth = rD.GetMonth()+nMonthDistance;
-    long nNewMonth = nMonth%12;
-    long nNewYear = rD.GetYear() + nMonth/12;
-    if( nMonth <= 0 || !nNewMonth )
-        nNewYear--;
-    if( nNewMonth <= 0 )
-        nNewMonth += 12;
-    aRet.SetMonth( sal_uInt16(nNewMonth) );
-    aRet.SetYear( sal_uInt16(nNewYear) );
-    aRet.Normalize();
+    aRet.AddMonths( nMonthDistance );
     return aRet;
 }
 
-Date DateHelper::GetDateSomeYearsAway( const Date& rD, long nYearDistance )
+Date DateHelper::GetDateSomeYearsAway( const Date& rD, sal_Int32 nYearDistance )
 {
     Date aRet(rD);
-    aRet.SetYear( static_cast<sal_uInt16>(rD.GetYear()+nYearDistance) );
-    aRet.Normalize();
+    aRet.AddYears( static_cast<sal_Int16>(nYearDistance) );
     return aRet;
 }
 
diff --git a/chart2/source/view/inc/DateHelper.hxx b/chart2/source/view/inc/DateHelper.hxx
index 3142e90c9f1d..099985533853 100644
--- a/chart2/source/view/inc/DateHelper.hxx
+++ b/chart2/source/view/inc/DateHelper.hxx
@@ -31,8 +31,8 @@ public:
     static bool IsInSameYear( const Date& rD1, const Date& rD2 );
     static bool IsInSameMonth( const Date& rD1, const Date& rD2 );
 
-    static Date GetDateSomeMonthsAway( const Date& rD, long nMonthDistance );
-    static Date GetDateSomeYearsAway( const Date& rD, long nYearDistance );
+    static Date GetDateSomeMonthsAway( const Date& rD, sal_Int32 nMonthDistance );
+    static Date GetDateSomeYearsAway( const Date& rD, sal_Int32 nYearDistance );
     static bool IsLessThanOneMonthAway( const Date& rD1, const Date& rD2 );
     static bool IsLessThanOneYearAway( const Date& rD1, const Date& rD2 );
 
diff --git a/connectivity/source/drivers/dbase/DTable.cxx b/connectivity/source/drivers/dbase/DTable.cxx
index 52215a4eef80..4c39e43e6d22 100644
--- a/connectivity/source/drivers/dbase/DTable.cxx
+++ b/connectivity/source/drivers/dbase/DTable.cxx
@@ -1218,7 +1218,7 @@ bool ODbaseTable::CreateFile(const INetURLObject& aFile, bool& bCreateMemo)
 
     m_pFileStream->Seek(0L);
     (*m_pFileStream).WriteUChar( nDbaseType );                            // dBase format
-    (*m_pFileStream).WriteUChar( aDate.GetYear() % 100 );                 // current date
+    (*m_pFileStream).WriteUChar( aDate.GetYearUnsigned() % 100 );         // current date
 
 
     (*m_pFileStream).WriteUChar( aDate.GetMonth() );
diff --git a/editeng/source/items/flditem.cxx b/editeng/source/items/flditem.cxx
index 4f2c03e4b23e..11309d4a0521 100644
--- a/editeng/source/items/flditem.cxx
+++ b/editeng/source/items/flditem.cxx
@@ -396,7 +396,7 @@ void SvxDateField::Load( SvPersistStream & rStm )
 {
     sal_uInt16 nType, nFormat;
 
-    rStm.ReadUInt32( nFixDate );
+    rStm.ReadInt32( nFixDate );
     rStm.ReadUInt16( nType );
     rStm.ReadUInt16( nFormat );
 
@@ -407,7 +407,7 @@ void SvxDateField::Load( SvPersistStream & rStm )
 
 void SvxDateField::Save( SvPersistStream & rStm )
 {
-    rStm.WriteUInt32( nFixDate );
+    rStm.WriteInt32( nFixDate );
     rStm.WriteUInt16( eType );
     rStm.WriteUInt16( eFormat );
 }
diff --git a/editeng/source/uno/unofield.cxx b/editeng/source/uno/unofield.cxx
index 6a26bcddf741..5a0dddd48186 100644
--- a/editeng/source/uno/unofield.cxx
+++ b/editeng/source/uno/unofield.cxx
@@ -176,7 +176,7 @@ static SvxFileFormat setFileNameDisplayFormat( sal_Int16 nFormat )
     }
 }
 
-static util::DateTime getDate( sal_uLong nDate )
+static util::DateTime getDate( sal_Int32 nDate )
 {
     util::DateTime aDate;
     memset( &aDate, 0, sizeof( util::DateTime ) );
diff --git a/i18npool/inc/calendar_gregorian.hxx b/i18npool/inc/calendar_gregorian.hxx
index 4f333815a918..4a16c00c3eb6 100644
--- a/i18npool/inc/calendar_gregorian.hxx
+++ b/i18npool/inc/calendar_gregorian.hxx
@@ -116,9 +116,9 @@ private:
 
     /** Submit fieldSetValue array according to fieldSet. */
     void submitFields() throw(css::uno::RuntimeException);
-    /** Submit fieldSetValue array according to fieldSet, plus YMDhms if >=0,
+    /** Submit fieldSetValue array according to fieldSet, plus EYMDhms if >=0,
         plus zone and DST if != 0 */
-    void submitValues( sal_Int32 nYear, sal_Int32 nMonth, sal_Int32 nDay, sal_Int32 nHour, sal_Int32 nMinute, sal_Int32 nSecond, sal_Int32 nMilliSecond, sal_Int32 nZone, sal_Int32 nDST) throw(css::uno::RuntimeException);
+    void submitValues( sal_Int32 nEra, sal_Int32 nYear, sal_Int32 nMonth, sal_Int32 nDay, sal_Int32 nHour, sal_Int32 nMinute, sal_Int32 nSecond, sal_Int32 nMilliSecond, sal_Int32 nZone, sal_Int32 nDST) throw(css::uno::RuntimeException);
     /** Set fields internally. */
     void setValue() throw(css::uno::RuntimeException);
     /** Obtain combined field values for timezone offset (minutes+secondmillis)
diff --git a/i18npool/source/calendar/calendar_gregorian.cxx b/i18npool/source/calendar/calendar_gregorian.cxx
index fc470e109e8e..275b24dff0ed 100644
--- a/i18npool/source/calendar/calendar_gregorian.cxx
+++ b/i18npool/source/calendar/calendar_gregorian.cxx
@@ -491,12 +491,14 @@ void Calendar_gregorian::submitFields() throw(css::uno::RuntimeException)
         body->set( fieldNameConverter( CalendarFieldIndex::DST_OFFSET), nDSTOffset);
 }
 
-void Calendar_gregorian::submitValues( sal_Int32 nYear,
+void Calendar_gregorian::submitValues( sal_Int32 nEra, sal_Int32 nYear,
         sal_Int32 nMonth, sal_Int32 nDay, sal_Int32 nHour, sal_Int32 nMinute,
         sal_Int32 nSecond, sal_Int32 nMilliSecond, sal_Int32 nZone, sal_Int32 nDST )
             throw(css::uno::RuntimeException)
 {
     submitFields();
+    if (nEra >= 0)
+        body->set( UCAL_ERA, nEra);
     if (nYear >= 0)
         body->set( UCAL_YEAR, nYear);
     if (nMonth >= 0)
@@ -567,12 +569,18 @@ void Calendar_gregorian::setValue() throw(RuntimeException)
 
     bool bNeedZone = !(fieldSet & (1 << CalendarFieldIndex::ZONE_OFFSET));
     bool bNeedDST  = !(fieldSet & (1 << CalendarFieldIndex::DST_OFFSET));
-    sal_Int32 nZone1, nDST1, nYear, nMonth, nDay, nHour, nMinute, nSecond, nMilliSecond, nZone0, nDST0;
+    sal_Int32 nZone1, nDST1, nEra, nYear, nMonth, nDay, nHour, nMinute, nSecond, nMilliSecond, nZone0, nDST0;
     nZone1 = nDST1 = nZone0 = nDST0 = 0;
-    nYear = nMonth = nDay = nHour = nMinute = nSecond = nMilliSecond = -1;
+    nEra = nYear = nMonth = nDay = nHour = nMinute = nSecond = nMilliSecond = -1;
     if ( bNeedZone || bNeedDST )
     {
         UErrorCode status;
+        if ( !(fieldSet & (1 << CalendarFieldIndex::ERA)) )
+        {
+            nEra = body->get( UCAL_ERA, status = U_ZERO_ERROR);
+            if ( !U_SUCCESS(status) )
+                nEra = -1;
+        }
         if ( !(fieldSet & (1 << CalendarFieldIndex::YEAR)) )
         {
             nYear = body->get( UCAL_YEAR, status = U_ZERO_ERROR);
@@ -629,7 +637,7 @@ void Calendar_gregorian::setValue() throw(RuntimeException)
         }
 
         // Submit values to obtain a time zone and DST corresponding to the date/time.
-        submitValues( nYear, nMonth, nDay, nHour, nMinute, nSecond, nMilliSecond, nZone0, nDST0);
+        submitValues( nEra, nYear, nMonth, nDay, nHour, nMinute, nSecond, nMilliSecond, nZone0, nDST0);
 
         DUMP_ICU_CAL_MSG(("%s\n","setValue() in bNeedZone||bNeedDST after submitValues()"));
         DUMP_I18N_CAL_MSG(("%s\n","setValue() in bNeedZone||bNeedDST after submitValues()"));
@@ -680,7 +688,7 @@ void Calendar_gregorian::setValue() throw(RuntimeException)
                 lcl_setCombinedOffsetFieldValues( nDST2, fieldSetValue,
                         fieldValue, CalendarFieldIndex::DST_OFFSET,
                         CalendarFieldIndex::DST_OFFSET_SECOND_MILLIS);
-            submitValues( nYear, nMonth, nDay, nHour, nMinute, nSecond, nMilliSecond, nZone2, nDST2);
+            submitValues( nEra, nYear, nMonth, nDay, nHour, nMinute, nSecond, nMilliSecond, nZone2, nDST2);
             DUMP_ICU_CAL_MSG(("%s\n","setValue() after Zone/DST glitch resubmit"));
             DUMP_I18N_CAL_MSG(("%s\n","setValue() after Zone/DST glitch resubmit"));
 
@@ -726,7 +734,7 @@ void Calendar_gregorian::setValue() throw(RuntimeException)
             }
             if (bResubmit)
             {
-                submitValues( nYear, nMonth, nDay, nHour, nMinute, nSecond, nMilliSecond, nZone3, nDST3);
+                submitValues( nEra, nYear, nMonth, nDay, nHour, nMinute, nSecond, nMilliSecond, nZone3, nDST3);
                 DUMP_ICU_CAL_MSG(("%s\n","setValue() after Zone/DST glitch 2nd resubmit"));
                 DUMP_I18N_CAL_MSG(("%s\n","setValue() after Zone/DST glitch 2nd resubmit"));
             }
diff --git a/include/editeng/flditem.hxx b/include/editeng/flditem.hxx
index 649167a20118..fd01faed6d83 100644
--- a/include/editeng/flditem.hxx
+++ b/include/editeng/flditem.hxx
@@ -106,7 +106,7 @@ enum SvxDateFormat {    SVXDATEFORMAT_APPDEFAULT = 0,   // Set as in App
 
 class EDITENG_DLLPUBLIC SvxDateField : public SvxFieldData
 {
-    sal_uInt32              nFixDate;
+    sal_Int32               nFixDate;
     SvxDateType             eType;
     SvxDateFormat           eFormat;
 
@@ -118,7 +118,7 @@ public:
                                 SvxDateType eType = SVXDATETYPE_VAR,
                                 SvxDateFormat eFormat = SVXDATEFORMAT_STDSMALL );
 
-    sal_uInt32              GetFixDate() const { return nFixDate; }
+    sal_Int32               GetFixDate() const { return nFixDate; }
     void                    SetFixDate( const Date& rDate ) { nFixDate = rDate.GetDate(); }
 
     SvxDateType             GetType() const { return eType; }
diff --git a/include/svl/zforlist.hxx b/include/svl/zforlist.hxx
index de78ae51b484..e28b4aeb2cfd 100644
--- a/include/svl/zforlist.hxx
+++ b/include/svl/zforlist.hxx
@@ -333,7 +333,7 @@ public:
     /// Change language/country, also input and format scanner
     void ChangeIntl( LanguageType eLnge );
     /// Change the reference null date
-    void ChangeNullDate(sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear);
+    void ChangeNullDate(sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear);
     /// Change standard precision
     void ChangeStandardPrec(short nPrec);
     /// Set zero value suppression
diff --git a/include/svtools/calendar.hxx b/include/svtools/calendar.hxx
index 144f78250821..3814d11a702b 100644
--- a/include/svtools/calendar.hxx
+++ b/include/svtools/calendar.hxx
@@ -146,7 +146,7 @@ calls or by ending a selection.
 
 #define DIB_BOLD                    ((sal_uInt16)0x0001)
 
-typedef std::set<sal_uInt32> IntDateSet;
+typedef std::set<sal_Int32> IntDateSet;
 
 
 class SVT_DLLPUBLIC Calendar : public Control
@@ -188,8 +188,8 @@ private:
     long            mnDayHeight;
     long            mnWeekWidth;
     WinBits         mnWinStyle;
-    sal_uInt16      mnFirstYear;
-    sal_uInt16      mnLastYear;
+    sal_Int16       mnFirstYear;
+    sal_Int16       mnLastYear;
     bool            mbCalc:1,
                     mbFormat:1,
                     mbDrag:1,
@@ -224,9 +224,9 @@ private:
     SVT_DLLPRIVATE sal_uInt16   ImplHitTest( const Point& rPos, Date& rDate ) const;
     SVT_DLLPRIVATE void         ImplDrawSpin(vcl::RenderContext& rRenderContext);
     SVT_DLLPRIVATE void         ImplDrawDate(vcl::RenderContext& rRenderContext, long nX, long nY,
-                                             sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear,
+                                             sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear,
                                              DayOfWeek eDayOfWeek,
-                                             bool bOther, sal_uLong nToday);
+                                             bool bOther, sal_Int32 nToday);
     SVT_DLLPRIVATE void         ImplDraw(vcl::RenderContext& rRenderContext);
     SVT_DLLPRIVATE void         ImplUpdateDate( const Date& rDate );
     SVT_DLLPRIVATE void         ImplUpdateSelection( IntDateSet* pOld );
diff --git a/include/tools/date.hxx b/include/tools/date.hxx
index 1dfb13098028..bab1efd833f8 100644
--- a/include/tools/date.hxx
+++ b/include/tools/date.hxx
@@ -27,15 +27,32 @@
 enum DayOfWeek { MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY,
                  SATURDAY, SUNDAY };
 
-// TODO FIXME: make it handle signed year?
+/** Represents a date in the proleptic Gregorian calendar.
+
+    Largest representable date is 32767-12-31 = 327671231
+
+    Smallest representable date is -32768-01-01 = -327680101
+
+    Due to possible conversions to css::util::Date, which has a short
+    Year member variable, these limits are fix.
+
+    Year value 0 is unused. The year before year 1 CE is year 1 BCE, which is
+    the traditional proleptic Gregorian calendar.
+
+    This is not how ISO 8601:2000 defines things (but ISO 8601:1998 Draft
+    Revision did), but it enables class Date to be used for writing XML files
+    as XML Schema Part 2 in D.3.2 No Year Zero says
+    "The year "0000" is an illegal year value.", see
+    https://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#noYearZero
+    and furthermore the note for 3.2.7 dateTime
+    https://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#dateTime
+
+ */
 class SAL_WARN_UNUSED TOOLS_DLLPUBLIC Date
 {
 private:
-    sal_uInt32      nDate;
-    void            setDateFromDMY( sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear )
-                        { nDate = (   sal_uInt32( nDay   % 100 ) ) +
-                                  ( ( sal_uInt32( nMonth % 100 ) ) * 100 ) +
-                                  ( ( sal_uInt32( nYear  % 10000 ) ) * 10000); }
+    sal_Int32       mnDate;
+    void            setDateFromDMY( sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear );
 
 public:
     enum DateInitSystem
@@ -43,37 +60,61 @@ public:
         SYSTEM
     };
 
-    // TODO temporary until all uses are inspected and resolved
     enum DateInitEmpty
     {
         EMPTY
     };
 
-                    Date( DateInitEmpty)
-                        { nDate = 0; }
-                    Date( DateInitSystem );
-                    Date( sal_uInt32 _nDate ) { Date::nDate = _nDate; }
-                    Date( const Date& rDate )
-                        { nDate = rDate.nDate; }
-                    Date( sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear )
+                    explicit Date( DateInitEmpty ) : mnDate(0) {}
+                    explicit Date( DateInitSystem );
+                    explicit Date( sal_Int32 nDate ) : mnDate(nDate) {}
+                    Date( const Date& rDate ) : mnDate(rDate.mnDate) {}
+                    Date( sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear )
                         { setDateFromDMY(nDay, nMonth, nYear); }
-                    Date( const css::util::Date& _rDate )
+                    Date( const css::util::Date& rUDate )
                     {
-                        SAL_WARN_IF(_rDate.Year < 0, "tools.datetime", "Negative year in css::util::Date to ::Date conversion");
-                        setDateFromDMY(_rDate.Day, _rDate.Month, _rDate.Year);
+                        setDateFromDMY(rUDate.Day, rUDate.Month, rUDate.Year);
                     }
                     Date( const css::util::DateTime& _rDateTime );
 
-    void            SetDate( sal_uInt32 nNewDate ) { nDate = nNewDate; }
-    sal_uInt32      GetDate() const { return nDate; }
+    void            SetDate( sal_Int32 nNewDate );
+    sal_Int32       GetDate() const { return mnDate; }
+    /** Type safe access for values that are guaranteed to be unsigned, like Date::SYSTEM. */
+    sal_uInt32      GetDateUnsigned() const { return static_cast<sal_uInt32>(mnDate < 0 ? -mnDate : mnDate); }
     css::util::Date GetUNODate() const { return css::util::Date(GetDay(), GetMonth(), GetYear()); }
 
     void            SetDay( sal_uInt16 nNewDay );
     void            SetMonth( sal_uInt16 nNewMonth );
-    void            SetYear( sal_uInt16 nNewYear );
-    sal_uInt16      GetDay() const { return (sal_uInt16)(nDate % 100); }
-    sal_uInt16      GetMonth() const { return (sal_uInt16)((nDate / 100) % 100); }
-    sal_uInt16      GetYear() const { return (sal_uInt16)(nDate / 10000); }
+    void            SetYear( sal_Int16 nNewYear );
+    sal_uInt16      GetDay() const
+                    {
+                        return mnDate < 0 ?
+                            static_cast<sal_uInt16>(-mnDate % 100) :
+                            static_cast<sal_uInt16>( mnDate % 100);
+                    }
+    sal_uInt16      GetMonth() const
+                    {
+                        return mnDate < 0 ?
+                            static_cast<sal_uInt16>((-mnDate / 100) % 100) :
+                            static_cast<sal_uInt16>(( mnDate / 100) % 100);
+                    }
+    sal_Int16       GetYear() const { return static_cast<sal_Int16>(mnDate / 10000); }
+    /** Type safe access for values that are guaranteed to be unsigned, like Date::SYSTEM. */
+    sal_uInt16      GetYearUnsigned() const { return static_cast<sal_uInt16>((mnDate < 0 ? -mnDate : mnDate) / 10000); }
+    sal_Int16       GetNextYear() const { sal_Int16 nY = GetYear(); return nY == -1 ? 1 : nY + 1; }
+    sal_Int16       GetPrevYear() const { sal_Int16 nY = GetYear(); return nY == 1 ? -1 : nY - 1; }
+
+    /** Add years skipping year 0 and truncating at limits. If the original
+        date was on Feb-29 and the resulting date is not a leap year, the
+        result is adjusted to Feb-28.
+    */
+    void            AddYears( sal_Int16 nAddYears );
+
+    /** Add months skipping year 0 and truncating at limits. If the original
+        date was on Feb-29 or day 31 and the resulting date is not a leap year
+        or a month with less days, the result is adjusted to Feb-28 or day 30.
+    */
+    void            AddMonths( sal_Int32 nAddMonths );
 
     /** Obtain the day of the week for the date.
 
@@ -146,24 +187,26 @@ public:
     bool            Normalize();
 
     bool            IsBetween( const Date& rFrom, const Date& rTo ) const
-                        { return ((nDate >= rFrom.nDate) &&
-                                 (nDate <= rTo.nDate)); }
+                        { return ((mnDate >= rFrom.mnDate) &&
+                                 (mnDate <= rTo.mnDate)); }
 
     bool            operator ==( const Date& rDate ) const
-                        { return (nDate == rDate.nDate); }
+                        { return (mnDate == rDate.mnDate); }
     bool            operator !=( const Date& rDate ) const
-                        { return (nDate != rDate.nDate); }
+                        { return (mnDate != rDate.mnDate); }
     bool            operator  >( const Date& rDate ) const
-                        { return (nDate > rDate.nDate); }
+                        { return (mnDate > rDate.mnDate); }
     bool            operator  <( const Date& rDate ) const
-                        { return (nDate < rDate.nDate); }
+                        { return (mnDate < rDate.mnDate); }
     bool            operator >=( const Date& rDate ) const
-                        { return (nDate >= rDate.nDate); }
+                        { return (mnDate >= rDate.mnDate); }
     bool            operator <=( const Date& rDate ) const
-                        { return (nDate <= rDate.nDate); }
+                        { return (mnDate <= rDate.mnDate); }
 
     Date&           operator =( const Date& rDate )
-                        { nDate = rDate.nDate; return *this; }
+                        { mnDate = rDate.mnDate; return *this; }
+    Date&           operator =( const css::util::Date& rUDate )
+                        { setDateFromDMY( rUDate.Day, rUDate.Month, rUDate.Year); return *this; }
     Date&           operator +=( long nDays );
     Date&           operator -=( long nDays );
     Date&           operator ++();
@@ -178,14 +221,14 @@ public:
         Internally sanitizes nMonth to values 1 <= nMonth <= 12, does not
         normalize values.
      */
-    static sal_uInt16 GetDaysInMonth( sal_uInt16 nMonth, sal_uInt16 nYear );
+    static sal_uInt16 GetDaysInMonth( sal_uInt16 nMonth, sal_Int16 nYear );
 
     /// Internally normalizes values.
-    static long DateToDays( sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear );
+    static long DateToDays( sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear );
     /// Semantically identical to IsValidDate() member method.
-    static bool IsValidDate( sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear );
+    static bool IsValidDate( sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear );
     /// Semantically identical to Normalize() member method.
-    static bool Normalize( sal_uInt16 & rDay, sal_uInt16 & rMonth, sal_uInt16 & rYear );
+    static bool Normalize( sal_uInt16 & rDay, sal_uInt16 & rMonth, sal_Int16 & rYear );
 
  private:
     /// An accelerated form of DateToDays on this date
diff --git a/include/tools/datetime.hxx b/include/tools/datetime.hxx
index 66826dff58e1..9e1f5f3fe6ea 100644
--- a/include/tools/datetime.hxx
+++ b/include/tools/datetime.hxx
@@ -34,14 +34,13 @@ public:
         SYSTEM
     };
 
-    // TODO temporary until all uses are inspected and resolved
     enum DateTimeInitEmpty
     {
         EMPTY
     };
 
-                    DateTime( DateTimeInitEmpty ) : Date( Date::EMPTY ), Time( Time::EMPTY ) {}
-                    DateTime( DateTimeInitSystem ) : Date( Date::SYSTEM ), Time( Time::SYSTEM ) {}
+                    explicit DateTime( DateTimeInitEmpty ) : Date( Date::EMPTY ), Time( Time::EMPTY ) {}
+                    explicit DateTime( DateTimeInitSystem ) : Date( Date::SYSTEM ), Time( Time::SYSTEM ) {}
                     DateTime( const DateTime& rDateTime ) :
                         Date( rDateTime ), Time( rDateTime ) {}
                     DateTime( const Date& rDate ) : Date( rDate ), Time(0) {}
@@ -103,6 +102,7 @@ public:
                         { return (const Date&) rDateTime - rDate; }
 
     DateTime&       operator =( const DateTime& rDateTime );
+    DateTime&       operator =( const css::util::DateTime& rUDateTime );
 
     void            GetWin32FileDateTime( sal_uInt32 & rLower, sal_uInt32 & rUpper );
     static DateTime CreateFromWin32FileDateTime( sal_uInt32 rLower, sal_uInt32 rUpper );
diff --git a/include/vcl/field.hxx b/include/vcl/field.hxx
index d07624e8a92c..d277a0a55b59 100644
--- a/include/vcl/field.hxx
+++ b/include/vcl/field.hxx
@@ -336,12 +336,12 @@ public:
     void                    SetEmptyDate();
     bool                    IsEmptyDate() const;
 
-    void                    ResetLastDate() { maLastDate = Date( 0, 0, 0 ); }
+    void                    ResetLastDate() { maLastDate = Date( Date::EMPTY ); }
 
     static void             ExpandCentury( Date& rDate );
     static void             ExpandCentury( Date& rDate, sal_uInt16 nTwoDigitYearStart );
 
-    static Date             GetInvalidDate() { return Date( 0, 0, 0 ); }
+    static Date             GetInvalidDate() { return Date( Date::EMPTY ); }
 
     /** enables or disables the enforcement of valid values
 
diff --git a/sc/inc/docoptio.hxx b/sc/inc/docoptio.hxx
index a5f3bbfdc298..529135bb9a37 100644
--- a/sc/inc/docoptio.hxx
+++ b/sc/inc/docoptio.hxx
@@ -73,9 +73,9 @@ public:
     double GetIterEps() const               { return fIterEps; }
     void   SetIterEps( double fEps )        { fIterEps = fEps; }
 
-    void   GetDate( sal_uInt16& rD, sal_uInt16& rM, sal_uInt16& rY ) const
+    void   GetDate( sal_uInt16& rD, sal_uInt16& rM, sal_Int16& rY ) const
                                         { rD = nDay; rM = nMonth; rY = nYear;}
-    void   SetDate (sal_uInt16 nD, sal_uInt16 nM, sal_uInt16 nY)
+    void   SetDate (sal_uInt16 nD, sal_uInt16 nM, sal_Int16 nY)
                                         { nDay = nD; nMonth = nM; nYear = nY; }
     sal_uInt16 GetTabDistance() const { return nTabDistance;}
     void   SetTabDistance( sal_uInt16 nTabDist ) {nTabDistance = nTabDist;}
diff --git a/sc/source/core/data/conditio.cxx b/sc/source/core/data/conditio.cxx
index 684498c8616c..cf7af863c188 100644
--- a/sc/source/core/data/conditio.cxx
+++ b/sc/source/core/data/conditio.cxx
@@ -1692,7 +1692,7 @@ bool ScCondDateFormatEntry::IsValid( const ScAddress& rPos ) const
         case condformat::LASTMONTH:
             if( rActDate.GetMonth() == 1 )
             {
-                if( aCellDate.GetMonth() == 12 && rActDate.GetYear() == aCellDate.GetYear() + 1 )
+                if( aCellDate.GetMonth() == 12 && rActDate.GetYear() == aCellDate.GetNextYear() )
                     return true;
             }
             else if( rActDate.GetYear() == aCellDate.GetYear() )
@@ -1721,7 +1721,7 @@ bool ScCondDateFormatEntry::IsValid( const ScAddress& rPos ) const
             }
             break;
         case condformat::LASTYEAR:
-            if( rActDate.GetYear() == aCellDate.GetYear() + 1 )
+            if( rActDate.GetYear() == aCellDate.GetNextYear() )
                 return true;
             break;
         case condformat::THISYEAR:
diff --git a/sc/source/core/data/poolhelp.cxx b/sc/source/core/data/poolhelp.cxx
index 40bae0aa690f..b469155f6968 100644
--- a/sc/source/core/data/poolhelp.cxx
+++ b/sc/source/core/data/poolhelp.cxx
@@ -78,7 +78,8 @@ void ScPoolHelper::UseDocOptions() const
 {
     if (pFormTable)
     {
-        sal_uInt16 d,m,y;
+        sal_uInt16 d,m;
+        sal_Int16 y;
         aOpt.GetDate( d,m,y );
         pFormTable->ChangeNullDate( d,m,y );
         pFormTable->ChangeStandardPrec( (sal_uInt16)aOpt.GetStdPrecision() );
@@ -102,7 +103,8 @@ SvNumberFormatter* ScPoolHelper::CreateNumberFormatter() const
     p->SetColorLink( LINK(m_pSourceDoc, ScDocument, GetUserDefinedColor) );
     p->SetEvalDateFormat(NF_EVALDATEFORMAT_INTL_FORMAT);
 
-    sal_uInt16 d,m,y;
+    sal_uInt16 d,m;
+    sal_Int16 y;
     aOpt.GetDate(d, m, y);
     p->ChangeNullDate(d, m, y);
     p->ChangeStandardPrec(aOpt.GetStdPrecision());
diff --git a/sc/source/core/tool/chgviset.cxx b/sc/source/core/tool/chgviset.cxx
index 50a784f8b390..938c26591e62 100644
--- a/sc/source/core/tool/chgviset.cxx
+++ b/sc/source/core/tool/chgviset.cxx
@@ -146,7 +146,7 @@ void ScChangeViewSettings::AdjustDateMode( const ScDocument& rDoc )
                 aFirstDateTime.SetTime( 0 );
             }
             aLastDateTime = Date( Date::SYSTEM );
-            aLastDateTime.SetYear( aLastDateTime.GetYear() + 100 );
+            aLastDateTime.AddYears( 100 );
         }
         break;
         default:
diff --git a/sc/source/core/tool/docoptio.cxx b/sc/source/core/tool/docoptio.cxx
index c8ee49a93795..a84f8ae15a48 100644
--- a/sc/source/core/tool/docoptio.cxx
+++ b/sc/source/core/tool/docoptio.cxx
@@ -212,7 +212,8 @@ ScDocCfg::ScDocCfg() :
     Sequence<Any> aValues;
     const Any* pValues = nullptr;
 
-    sal_uInt16 nDateDay, nDateMonth, nDateYear;
+    sal_uInt16 nDateDay, nDateMonth;
+    sal_Int16 nDateYear;
     GetDate( nDateDay, nDateMonth, nDateYear );
 
     aNames = GetCalcPropertyNames();
@@ -246,7 +247,7 @@ ScDocCfg::ScDocCfg() :
                         if (pValues[nProp] >>= nIntVal) nDateMonth = (sal_uInt16) nIntVal;
                         break;
                     case SCCALCOPT_DATE_YEAR:
-                        if (pValues[nProp] >>= nIntVal) nDateYear = (sal_uInt16) nIntVal;
+                        if (pValues[nProp] >>= nIntVal) nDateYear = (sal_Int16) nIntVal;
                         break;
                     case SCCALCOPT_DECIMALS:
                         if (pValues[nProp] >>= nIntVal) SetStdPrecision( (sal_uInt16) nIntVal );
@@ -310,7 +311,8 @@ IMPL_LINK_NOARG_TYPED(ScDocCfg, CalcCommitHdl, ScLinkConfigItem&, void)
     Sequence<Any> aValues(aNames.getLength());
     Any* pValues = aValues.getArray();
 
-    sal_uInt16 nDateDay, nDateMonth, nDateYear;
+    sal_uInt16 nDateDay, nDateMonth;
+    sal_Int16 nDateYear;
     GetDate( nDateDay, nDateMonth, nDateYear );
 
     for(int nProp = 0; nProp < aNames.getLength(); nProp++)
diff --git a/sc/source/core/tool/interpr2.cxx b/sc/source/core/tool/interpr2.cxx
index fe4331431c02..cc735270d4fd 100644
--- a/sc/source/core/tool/interpr2.cxx
+++ b/sc/source/core/tool/interpr2.cxx
@@ -807,7 +807,8 @@ void ScInterpreter::ScGetDateDif()
         }
 
         // split dates in day, month, year for use with formats other than "d"
-        sal_uInt16 d1, m1, y1, d2, m2, y2;
+        sal_uInt16 d1, m1, d2, m2;
+        sal_Int16 y1, y2;
         Date aDate1( *( pFormatter->GetNullDate()));
         aDate1 += (long) ::rtl::math::approxFloor( nDate1 );
         y1 = aDate1.GetYear();
@@ -819,6 +820,12 @@ void ScInterpreter::ScGetDateDif()
         m2 = aDate2.GetMonth();
         d2 = aDate2.GetDay();
 
+        // Close the year 0 gap to calculate year difference.
+        if (y1 < 0 && y2 > 0)
+            ++y1;
+        else if (y1 > 0 && y2 < 0)
+            ++y2;
+
         if (  aInterval.equalsIgnoreAsciiCase( "m" ) )
         {
             // Return number of months.
@@ -871,7 +878,7 @@ void ScInterpreter::ScGetDateDif()
             {
                 if (m2 == 1)
                 {
-                    aDate1.SetYear( y2 - 1 );
+                    aDate1.SetYear( y2 == 1 ? -1 : y2 - 1 );
                     aDate1.SetMonth( 12 );
                 }
                 else
diff --git a/sc/source/ui/cctrl/checklistmenu.cxx b/sc/source/ui/cctrl/checklistmenu.cxx
index 32e2e11364fa..93f9aef01da0 100644
--- a/sc/source/ui/cctrl/checklistmenu.cxx
+++ b/sc/source/ui/cctrl/checklistmenu.cxx
@@ -1442,7 +1442,7 @@ void ScCheckListMenuWindow::addDateMember(const OUString& rsName, double nVal, b
     Date aDate = *(pFormatter->GetNullDate());
     aDate += static_cast<long>(rtl::math::approxFloor(nVal));
 
-    sal_uInt16 nYear = aDate.GetYear();
+    sal_Int16 nYear = aDate.GetYear();
     sal_uInt16 nMonth = aDate.GetMonth();
     sal_uInt16 nDay = aDate.GetDay();
 
diff --git a/sc/source/ui/optdlg/tpcalc.cxx b/sc/source/ui/optdlg/tpcalc.cxx
index 9cf30a177009..a9834f4e69aa 100644
--- a/sc/source/ui/optdlg/tpcalc.cxx
+++ b/sc/source/ui/optdlg/tpcalc.cxx
@@ -112,7 +112,8 @@ VclPtr<SfxTabPage> ScTpCalcOptions::Create( vcl::Window* pParent, const SfxItemS
 
 void ScTpCalcOptions::Reset( const SfxItemSet* /* rCoreAttrs */ )
 {
-    sal_uInt16  d,m,y;
+    sal_uInt16  d,m;
+    sal_Int16   y;
 
     *pLocalOptions  = *pOldOptions;
 
diff --git a/sc/source/ui/unoobj/optuno.cxx b/sc/source/ui/unoobj/optuno.cxx
index 925af4e63c26..ff479fe92677 100644
--- a/sc/source/ui/unoobj/optuno.cxx
+++ b/sc/source/ui/unoobj/optuno.cxx
@@ -162,7 +162,8 @@ uno::Any ScDocOptionsHelper::getPropertyValue(
         break;
         case PROP_UNO_NULLDATE:
         {
-            sal_uInt16 nD, nM, nY;
+            sal_uInt16 nD, nM;
+            sal_Int16 nY;
             rOptions.GetDate( nD, nM, nY );
             util::Date aDate( nD, nM, nY );
             aRet <<= aDate;
diff --git a/sfx2/source/doc/objcont.cxx b/sfx2/source/doc/objcont.cxx
index ea1ea377a365..bac439a9247d 100644
--- a/sfx2/source/doc/objcont.cxx
+++ b/sfx2/source/doc/objcont.cxx
@@ -245,7 +245,7 @@ void SfxObjectShell::UpdateTime_Impl(
     if (aNow.GetDate()>=pImpl->nTime.GetDate())
     {
         // Get count of days last editing.
-        nDays = aNow.GetSecFromDateTime(pImpl->nTime.GetDate())/86400 ;
+        nDays = aNow.GetSecFromDateTime(Date(pImpl->nTime.GetDate()))/86400 ;
 
         if (nDays==0)
         {
diff --git a/solenv/gdb/libreoffice/tl.py b/solenv/gdb/libreoffice/tl.py
index 87e4924e0d99..2e096fc8d26c 100644
--- a/solenv/gdb/libreoffice/tl.py
+++ b/solenv/gdb/libreoffice/tl.py
@@ -112,10 +112,12 @@ class DateImpl(DateTimeImpl):
 
     @staticmethod
     def parse(val):
-        date = val['nDate']
-        d = date % 100
-        m = (date / 100) % 100
+        date = val['mnDate']
         y = date / 10000
+        if date < 0:
+            date = -date
+        m = (date / 100) % 100
+        d = date % 100
         return DateImpl(y, m, d)
 
 class DatePrinter(object):
diff --git a/svl/source/numbers/zforfind.cxx b/svl/source/numbers/zforfind.cxx
index 6154e2a9bb78..7fc7f8c079fd 100644
--- a/svl/source/numbers/zforfind.cxx
+++ b/svl/source/numbers/zforfind.cxx
@@ -3406,7 +3406,7 @@ void ImpSvNumberInputScan::InvalidateDateAcceptancePatterns()
 
 void ImpSvNumberInputScan::ChangeNullDate( const sal_uInt16 Day,
                                            const sal_uInt16 Month,
-                                           const sal_uInt16 Year )
+                                           const sal_Int16 Year )
 {
     if ( pNullDate )
     {
diff --git a/svl/source/numbers/zforfind.hxx b/svl/source/numbers/zforfind.hxx
index 7cabce77cf2a..5f62e281f10c 100644
--- a/svl/source/numbers/zforfind.hxx
+++ b/svl/source/numbers/zforfind.hxx
@@ -40,7 +40,7 @@ public:
     /// set reference date for offset calculation
     void ChangeNullDate( const sal_uInt16 nDay,
                          const sal_uInt16 nMonth,
-                         const sal_uInt16 nYear );
+                         const sal_Int16 nYear );
 
     /// convert input string to number
     bool IsNumberFormat( const OUString& rString,            /// input string
diff --git a/svl/source/numbers/zforlist.cxx b/svl/source/numbers/zforlist.cxx
index bd67e25e9c09..5ca78ed0b370 100644
--- a/svl/source/numbers/zforlist.cxx
+++ b/svl/source/numbers/zforlist.cxx
@@ -398,7 +398,7 @@ Color* SvNumberFormatter::GetUserDefColor(sal_uInt16 nIndex)
 
 void SvNumberFormatter::ChangeNullDate(sal_uInt16 nDay,
                                        sal_uInt16 nMonth,
-                                       sal_uInt16 nYear)
+                                       sal_Int16 nYear)
 {
     pFormatScanner->ChangeNullDate(nDay, nMonth, nYear);
     pStringScanner->ChangeNullDate(nDay, nMonth, nYear);
diff --git a/svl/source/numbers/zforscan.cxx b/svl/source/numbers/zforscan.cxx
index b208364d5e95..8025ae6fd1e0 100644
--- a/svl/source/numbers/zforscan.cxx
+++ b/svl/source/numbers/zforscan.cxx
@@ -446,7 +446,7 @@ void ImpSvNumberformatScan::SetDependentKeywords()
     InitCompatCur();
 }
 
-void ImpSvNumberformatScan::ChangeNullDate(sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear)
+void ImpSvNumberformatScan::ChangeNullDate(sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear)
 {
     if ( pNullDate )
         *pNullDate = Date(nDay, nMonth, nYear);
diff --git a/svl/source/numbers/zforscan.hxx b/svl/source/numbers/zforscan.hxx
index 82535fd1e84a..bf92049bae1f 100644
--- a/svl/source/numbers/zforscan.hxx
+++ b/svl/source/numbers/zforscan.hxx
@@ -44,7 +44,7 @@ public:
     ~ImpSvNumberformatScan();
     void ChangeIntl(); // Replaces Keywords
 
-    void ChangeNullDate(sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear); // Replaces reference date
+    void ChangeNullDate(sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear); // Replaces reference date
     void ChangeStandardPrec(sal_uInt16 nPrec); // Replaces standard precision
 
     sal_Int32 ScanFormat( OUString& rString ); // Call scan analysis
diff --git a/svtools/source/control/calendar.cxx b/svtools/source/control/calendar.cxx
index 575463bd3912..b89b9061fde0 100644
--- a/svtools/source/control/calendar.cxx
+++ b/svtools/source/control/calendar.cxx
@@ -453,8 +453,8 @@ void Calendar::ImplFormat()
     }
 
     // get DateInfo
-    sal_uInt16 nNewFirstYear = maFirstDate.GetYear();
-    sal_uInt16 nNewLastYear = GetLastDate().GetYear();
+    sal_Int16 nNewFirstYear = maFirstDate.GetYear();
+    sal_Int16 nNewLastYear = GetLastDate().GetYear();
     if ( mnFirstYear )
     {
         if ( nNewFirstYear < mnFirstYear )
@@ -670,9 +670,9 @@ void Calendar::ImplDrawSpin(vcl::RenderContext& rRenderContext )
 
 void Calendar::ImplDrawDate(vcl::RenderContext& rRenderContext,
                             long nX, long nY,
-                            sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear,
+                            sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear,
                             DayOfWeek eDayOfWeek,
-                            bool bOther, sal_uLong nToday )
+                            bool bOther, sal_Int32 nToday )
 {
     Color* pTextColor = nullptr;
     const OUString& rDay = maDayTexts[nDay - 1];
@@ -769,10 +769,10 @@ void Calendar::ImplDraw(vcl::RenderContext& rRenderContext)
     long nDeltaY;
     long nDayX;
     long nDayY;
-    sal_uLong nToday = Date(Date::SYSTEM).GetDate();
+    sal_Int32 nToday = Date(Date::SYSTEM).GetDate();
     sal_uInt16 nDay;
     sal_uInt16 nMonth;
-    sal_uInt16 nYear;
+    sal_Int16 nYear;
     Date aDate = GetFirstMonth();
     DayOfWeek eStartDay = ImplGetWeekStart();
 
@@ -1559,7 +1559,7 @@ void Calendar::RequestHelp( const HelpEvent& rHEvt )
                 if ( (nMonth == 12) && (nWeek == 1) )
                 {
                     aStr += ",  ";
-                    aStr += OUString::number(aDate.GetYear()+1);
+                    aStr += OUString::number(aDate.GetNextYear());
                 }
                 else if ( (nMonth == 1) && (nWeek > 50) )
                 {
@@ -1761,7 +1761,7 @@ Date Calendar::GetFirstMonth() const
     if ( maFirstDate.GetDay() > 1 )
     {
         if ( maFirstDate.GetMonth() == 12 )
-            return Date( 1, 1, maFirstDate.GetYear()+1 );
+            return Date( 1, 1, maFirstDate.GetNextYear() );
         else
             return Date( 1, maFirstDate.GetMonth()+1, maFirstDate.GetYear() );
     }
@@ -2155,7 +2155,7 @@ CalendarField::CalendarField(vcl::Window* pParent, WinBits nWinStyle)
     , mnCalendarStyle(0)
     , mpTodayBtn(nullptr)
     , mpNoneBtn(nullptr)
-    , maDefaultDate( 0, 0, 0 )
+    , maDefaultDate( Date::EMPTY )
     , mbToday(false)
     , mbNone(false)
 {
diff --git a/svx/source/dialog/ctredlin.cxx b/svx/source/dialog/ctredlin.cxx
index 677cc081497a..40de9bac9d45 100644
--- a/svx/source/dialog/ctredlin.cxx
+++ b/svx/source/dialog/ctredlin.cxx
@@ -170,8 +170,7 @@ void SvxRedlinTable::SetCalcView()
 void SvxRedlinTable::UpdateFilterTest()
 {
     Date aDateMax( Date::SYSTEM );
-    sal_uInt16 nYEAR=aDateMax.GetYear()+100;
-    aDateMax.SetYear(nYEAR);
+    aDateMax.AddYears(100);
     Date aDateMin(1,1,1989);
     tools::Time aTMin(0);
     tools::Time aTMax(23,59,59);
diff --git a/sw/inc/docufld.hxx b/sw/inc/docufld.hxx
index 4a0b91bd5224..f14b3b7b00b6 100644
--- a/sw/inc/docufld.hxx
+++ b/sw/inc/docufld.hxx
@@ -464,7 +464,7 @@ public:
     virtual SwField*        Copy() const override;
 
     const DateTime&         GetDateTime() const             { return aDateTime; }
-    inline const Date       GetDate() const                 { return aDateTime.GetDate(); }
+    inline const Date       GetDate() const                 { return Date(aDateTime.GetDate()); }
     inline const tools::Time GetTime() const                 { return aDateTime.GetTime(); }
 
     /// Author
diff --git a/sw/source/core/fields/flddat.cxx b/sw/source/core/fields/flddat.cxx
index 358a20740e0c..e6e11451df72 100644
--- a/sw/source/core/fields/flddat.cxx
+++ b/sw/source/core/fields/flddat.cxx
@@ -152,7 +152,7 @@ tools::Time SwDateTimeField::GetTime() const
 {
     double fDummy;
     double fFract = modf(GetValue(), &fDummy);
-    DateTime aDT((long)fDummy, 0);
+    DateTime aDT(Date(static_cast<sal_Int32>(fDummy)), 0);
     aDT += fFract;
     return static_cast<tools::Time>(aDT);
 }
diff --git a/sw/source/core/unocore/unocrsrhelper.cxx b/sw/source/core/unocore/unocrsrhelper.cxx
index 4e935d6fe8ea..462b19df73b6 100644
--- a/sw/source/core/unocore/unocrsrhelper.cxx
+++ b/sw/source/core/unocore/unocrsrhelper.cxx
@@ -1192,8 +1192,7 @@ void makeRedline( SwPaM& rPaM,
     aDateTimeValue = aPropMap.getUnpackedValueOrDefault("RedlineDateTime", aDateTimeValue);
     if( aDateTimeValue >>= aStamp )
     {
-       aRedlineData.SetTimeStamp(
-        DateTime( Date( aStamp.Day, aStamp.Month, aStamp.Year ), tools::Time( aStamp.Hours, aStamp.Minutes, aStamp.Seconds ) ) );
+        aRedlineData.SetTimeStamp( DateTime( aStamp));
     }
 
     SwRedlineExtraData_FormattingChanges* pRedlineExtraData = nullptr;
diff --git a/sw/source/core/unocore/unofield.cxx b/sw/source/core/unocore/unofield.cxx
index e2efdad70749..36bf54b9d291 100644
--- a/sw/source/core/unocore/unofield.cxx
+++ b/sw/source/core/unocore/unofield.cxx
@@ -1357,12 +1357,7 @@ throw (lang::IllegalArgumentException, uno::RuntimeException, std::exception)
                 DateTime aDateTime( DateTime::EMPTY );
                 if (m_pImpl->m_pProps->pDateTime)
                 {
-                    aDateTime.SetYear(m_pImpl->m_pProps->pDateTime->Year);
-                    aDateTime.SetMonth(m_pImpl->m_pProps->pDateTime->Month);
-                    aDateTime.SetDay(m_pImpl->m_pProps->pDateTime->Day);
-                    aDateTime.SetHour(m_pImpl->m_pProps->pDateTime->Hours);
-                    aDateTime.SetMin(m_pImpl->m_pProps->pDateTime->Minutes);
-                    aDateTime.SetSec(m_pImpl->m_pProps->pDateTime->Seconds);
+                    aDateTime = *(m_pImpl->m_pProps->pDateTime);
                 }
                 SwPostItField* pPostItField = new SwPostItField(
                     static_cast<SwPostItFieldType*>(pFieldType),
diff --git a/sw/source/filter/ww8/docxattributeoutput.cxx b/sw/source/filter/ww8/docxattributeoutput.cxx
index 4e55c49055fe..f4d2c8168410 100644
--- a/sw/source/filter/ww8/docxattributeoutput.cxx
+++ b/sw/source/filter/ww8/docxattributeoutput.cxx
@@ -4584,9 +4584,7 @@ void DocxAttributeOutput::WritePostponedFormControl(const SdrObject* pObject)
                 {
                     css::util::Date aUNODate;
                     aGrabBag[i].Value >>= aUNODate;
-                    aOriginalDate.SetDay(aUNODate.Day);
-                    aOriginalDate.SetMonth(aUNODate.Month);
-                    aOriginalDate.SetYear(aUNODate.Year);
+                    aOriginalDate = aUNODate;
                 }
                 else if (aGrabBag[i].Name == "CharFormat")
                     aGrabBag[i].Value >>= aCharFormat;
diff --git a/tools/CppunitTest_tools_test.mk b/tools/CppunitTest_tools_test.mk
index e90b52457244..aced4bf6698a 100644
--- a/tools/CppunitTest_tools_test.mk
+++ b/tools/CppunitTest_tools_test.mk
@@ -15,6 +15,7 @@ $(eval $(call gb_CppunitTest_use_external,tools_test,boost_headers))
 
 $(eval $(call gb_CppunitTest_add_exception_objects,tools_test, \
     tools/qa/cppunit/test_bigint \
+    tools/qa/cppunit/test_date \
     tools/qa/cppunit/test_fract \
     tools/qa/cppunit/test_inetmime \
     tools/qa/cppunit/test_pathutils \
diff --git a/tools/qa/cppunit/test_date.cxx b/tools/qa/cppunit/test_date.cxx
new file mode 100644
index 000000000000..0ee30089b7b5
--- /dev/null
+++ b/tools/qa/cppunit/test_date.cxx
@@ -0,0 +1,76 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <cppunit/TestFixture.h>
+#include <cppunit/extensions/HelperMacros.h>
+
+#include <tools/date.hxx>
+
+namespace tools
+{
+
+class DateTest : public CppUnit::TestFixture
+{
+public:
+    void testDate();
+
+    CPPUNIT_TEST_SUITE(DateTest);
+    CPPUNIT_TEST(testDate);
+    CPPUNIT_TEST_SUITE_END();
+};
+
+void DateTest::testDate()
+{
+    const Date aCE(1,1,1);          // first day CE
+    const Date aBCE(31,12,-1);      // last day BCE
+    const Date aMin(1,1,-32768);    // minimum date
+    const Date aMax(31,12,32767);   // maximum date
+    Date aDate(Date::EMPTY);
+    const long kMinDays = -11968265;
+    const long kMaxDays =  11967900;
+
+    // Last day BCE to first day CE is 1 day difference.
+    CPPUNIT_ASSERT_EQUAL( static_cast<long>(1), aCE - aBCE);
+    CPPUNIT_ASSERT_EQUAL( static_cast<long>(-1), aBCE - aCE);
+    aDate = aBCE;
+    CPPUNIT_ASSERT_EQUAL( aCE.GetDate(), (aDate += 1).GetDate());
+    aDate = aCE;
+    CPPUNIT_ASSERT_EQUAL( aBCE.GetDate(), (aDate -= 1).GetDate());
+
+    // The entire BCE and CE ranges cover that many days. Day 0 is -0001-12-31
+    CPPUNIT_ASSERT_EQUAL( kMaxDays, aMax - aBCE);
+    CPPUNIT_ASSERT_EQUAL( kMinDays, aMin - aBCE);
+
+    // Truncate at limits, not under-/overflow or wrap.
+    aDate = aMin;
+    CPPUNIT_ASSERT_EQUAL( aMin.GetDate(), (aDate -= 1).GetDate());
+    aDate = aMax;
+    CPPUNIT_ASSERT_EQUAL( aMax.GetDate(), (aDate += 1).GetDate());
+    aDate = aBCE;
+    CPPUNIT_ASSERT_EQUAL( aMin.GetDate(), (aDate += (kMinDays-10)).GetDate());
+    aDate = aBCE;
+    CPPUNIT_ASSERT_EQUAL( aMax.GetDate(), (aDate += (kMaxDays+10)).GetDate());
+
+    // Year -1 is a leap year.
+    aDate = Date(28,2,-1);
+    CPPUNIT_ASSERT_EQUAL( Date(29,2,-1).GetDate(), (aDate += 1).GetDate());
+    aDate = Date(1,3,-1);
+    CPPUNIT_ASSERT_EQUAL( Date(29,2,-1).GetDate(), (aDate -= 1).GetDate());
+    // Year -5 is a leap year.
+    aDate = Date(28,2,-5);
+    CPPUNIT_ASSERT_EQUAL( Date(29,2,-5).GetDate(), (aDate += 1).GetDate());
+    aDate = Date(1,3,-5);
+    CPPUNIT_ASSERT_EQUAL( Date(29,2,-5).GetDate(), (aDate -= 1).GetDate());
+}
+
+CPPUNIT_TEST_SUITE_REGISTRATION(DateTest);
+
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */
diff --git a/tools/source/datetime/datetime.cxx b/tools/source/datetime/datetime.cxx
index cc0fc13a9ae6..d24f6f818184 100644
--- a/tools/source/datetime/datetime.cxx
+++ b/tools/source/datetime/datetime.cxx
@@ -25,6 +25,13 @@ DateTime::DateTime( const css::util::DateTime& rDateTime )
 {
 }
 
+DateTime& DateTime::operator =( const css::util::DateTime& rUDateTime )
+{
+    Date::operator=( Date( rUDateTime.Day, rUDateTime.Month, rUDateTime.Year));
+    Time::operator=( Time( rUDateTime));
+    return *this;
+}
+
 bool DateTime::IsBetween( const DateTime& rFrom, const DateTime& rTo ) const
 {
     if ( (*this >= rFrom) && (*this <= rTo) )
diff --git a/tools/source/datetime/tdate.cxx b/tools/source/datetime/tdate.cxx
index 78b1ec63ac70..e4556be8c1c0 100644
--- a/tools/source/datetime/tdate.cxx
+++ b/tools/source/datetime/tdate.cxx
@@ -29,36 +29,64 @@
 static const sal_uInt16 aDaysInMonth[12] = { 31, 28, 31, 30, 31, 30,
                                              31, 31, 30, 31, 30, 31 };
 
-// The number of days we internally handle.
+// Once upon a time the number of days we internally handled was limited to
+// MAX_DAYS 3636532. That changed with a full 16-bit year.
 // Assuming the first valid positive date in a proleptic Gregorian calendar is
-// 0001-01-01, this results in an end date of 9957-06-26.
+// 0001-01-01, this resulted in an end date of 9957-06-26.
 // Hence we documented that years up to and including 9956 are handled.
 /* XXX: it is unclear history why this value was chosen, the representable
  * 9999-12-31 would be 3652060 days from 0001-01-01. Even 9998-12-31 to
- * distinguish from a maximum possible date would be 3651695. Better keep the
- * value in case something somewhere relies on it or there is another reason
- * beyond..
- * At least connectivity/source/commontools/dbconversion.cxx has the same
- * value to calculate with css::util::Date */
-#define MAX_DAYS    3636532
+ * distinguish from a maximum possible date would be 3651695.
+ * There is connectivity/source/commontools/dbconversion.cxx that still has the
+ * same value to calculate with css::util::Date */
+/* XXX can that dbconversion cope with years > 9999 or negative years at all?
+ * Database fields may be limited to positive 4 digits. */
+
+static const long MIN_DAYS = -11968265;     // -32768-01-01
+static const long MAX_DAYS =  11967900;     //  32767-12-31
 
 namespace
 {
 
-inline long ImpYearToDays( sal_uInt16 nYear )
+const sal_Int16 kYearMax = SAL_MAX_INT16;
+const sal_Int16 kYearMin = SAL_MIN_INT16;
+
+// Days until start of year from zero, so month and day of month can be added.
+// year 1 => 0 days, year 2 => 365 days, ...
+// year -1 => -366 days, year -2 => -731 days, ...
+inline long ImpYearToDays( sal_Int16 nYear )
 {
-    const long nYr(static_cast<long>(nYear) - 1);
-    return nYr*365 + nYr/4 - nYr/100 + nYr/400;
+    assert( nYear != 0 );
+    long nOffset;
+    long nYr;
+    if (nYear < 0)
+    {
+        nOffset = -366;
+        nYr = nYear + 1;
+    }
+    else
+    {
+        nOffset = 0;
+        nYr = nYear - 1;
+    }
+    return nOffset + nYr*365 + nYr/4 - nYr/100 + nYr/400;
 }
 
-inline bool ImpIsLeapYear( sal_uInt16 nYear )
+inline bool ImpIsLeapYear( sal_Int16 nYear )
 {
+    // Leap years BCE are -1, -5, -9, ...
+    // See
+    // https://en.wikipedia.org/wiki/Proleptic_Gregorian_calendar#Usage
+    // https://en.wikipedia.org/wiki/0_(year)#History_of_astronomical_usage
+    assert( nYear != 0 );
+    if (nYear < 0)
+        nYear = -nYear - 1;
     return ( ( ((nYear % 4) == 0) && ((nYear % 100) != 0) ) ||
              ( (nYear % 400) == 0 ) );
 }
 
 // All callers must have sanitized or normalized month and year values!
-inline sal_uInt16 ImplDaysInMonth( sal_uInt16 nMonth, sal_uInt16 nYear )
+inline sal_uInt16 ImplDaysInMonth( sal_uInt16 nMonth, sal_Int16 nYear )
 {
     if ( nMonth != 2 )
         return aDaysInMonth[nMonth-1];
@@ -73,8 +101,29 @@ inline sal_uInt16 ImplDaysInMonth( sal_uInt16 nMonth, sal_uInt16 nYear )
 
 }
 
+void Date::setDateFromDMY( sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear )
+{
+    SAL_WARN_IF( nYear == 0, "tools","Date::setDateFromDMY - sure about 0 year? It's not in the calendar.");
+    if (nYear < 0)
+        mnDate =
+            (static_cast<sal_Int32>( nYear        ) * 10000) -
+            (static_cast<sal_Int32>( nMonth % 100 ) * 100) -
+            (static_cast<sal_Int32>( nDay   % 100 ));
+    else
+        mnDate =
+            (static_cast<sal_Int32>( nYear        ) * 10000) +
+            (static_cast<sal_Int32>( nMonth % 100 ) * 100) +
+            (static_cast<sal_Int32>( nDay   % 100 ));
+}
+
+void Date::SetDate( sal_Int32 nNewDate )
+{
+    assert( ((nNewDate / 10000) != 0) && "you don't want to set a 0 year, do you?" );
+    mnDate = nNewDate;
+}
+
 // static
-sal_uInt16 Date::GetDaysInMonth( sal_uInt16 nMonth, sal_uInt16 nYear )
+sal_uInt16 Date::GetDaysInMonth( sal_uInt16 nMonth, sal_Int16 nYear )
 {
     SAL_WARN_IF( nMonth < 1 || 12 < nMonth, "tools", "Date::GetDaysInMonth - nMonth out of bounds " << nMonth);
     if (nMonth < 1)
@@ -87,7 +136,7 @@ sal_uInt16 Date::GetDaysInMonth( sal_uInt16 nMonth, sal_uInt16 nYear )
 long Date::GetAsNormalizedDays() const
 {
     // This is a very common datum we often calculate from.
-    if (nDate == 18991230) // 1899-12-30
+    if (mnDate == 18991230) // 1899-12-30
     {
         assert(DateToDays( GetDay(), GetMonth(), GetYear() ) == 693594);
         return 693594;
@@ -95,7 +144,7 @@ long Date::GetAsNormalizedDays() const
     return DateToDays( GetDay(), GetMonth(), GetYear() );
 }
 
-long Date::DateToDays( sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear )
+long Date::DateToDays( sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear )
 {
     Normalize( nDay, nMonth, nYear);
 
@@ -108,25 +157,28 @@ long Date::DateToDays( sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear )
 
 static Date lcl_DaysToDate( long nDays )
 {
+    if ( nDays <= MIN_DAYS )
+        return Date( 1, 1, kYearMin );
     if ( nDays >= MAX_DAYS )
-        return Date( 31, 12, 9999 );
-
-    if ( nDays <= 0 )
-        return Date( 1, 0, 0 );
+        return Date( 31, 12, kYearMax );
 
-    long    nTempDays;
-    long    i = 0;
-    bool    bCalc;
+    // Day 0 is -0001-12-31, day 1 is 0001-01-01
+    const sal_Int16 nSign = (nDays <= 0 ? -1 : 1);
+    long nTempDays;
+    long i = 0;
+    bool bCalc;
 
-    sal_uInt16 nYear;
+    sal_Int16 nYear;
     do
     {
-        nYear = (sal_uInt16)((nDays / 365) - i);
+        nYear = static_cast<sal_Int16>((nDays / 365) - (i * nSign));
+        if (nYear == 0)
+            nYear = nSign;
         nTempDays = nDays - ImpYearToDays(nYear);
         bCalc = false;
         if ( nTempDays < 1 )
         {
-            i++;
+            i += nSign;
             bCalc = true;
         }
         else
@@ -135,7 +187,7 @@ static Date lcl_DaysToDate( long nDays )
             {
                 if ( (nTempDays != 366) || !ImpIsLeapYear( nYear ) )
                 {
-                    i--;
+                    i -= nSign;
                     bCalc = true;
                 }
             }
@@ -147,7 +199,7 @@ static Date lcl_DaysToDate( long nDays )
     while ( nTempDays > static_cast<long>(ImplDaysInMonth( nMonth, nYear )) )
     {
         nTempDays -= ImplDaysInMonth( nMonth, nYear );
-        nMonth++;
+        ++nMonth;
     }
 
     return Date( static_cast<sal_uInt16>(nTempDays), nMonth, nYear );
@@ -195,11 +247,73 @@ void Date::SetMonth( sal_uInt16 nNewMonth )
     setDateFromDMY( GetDay(), nNewMonth, GetYear() );
 }
 
-void Date::SetYear( sal_uInt16 nNewYear )
+void Date::SetYear( sal_Int16 nNewYear )
 {
+    assert( nNewYear != 0 );
     setDateFromDMY( GetDay(), GetMonth(), nNewYear );
 }
 
+void Date::AddYears( sal_Int16 nAddYears )
+{
+    sal_Int16 nYear = GetYear();
+    if (nYear < 0)
+    {
+        if (nAddYears < 0)
+        {
+            if (nYear < kYearMin - nAddYears)
+                nYear = kYearMin;
+            else
+                nYear += nAddYears;
+        }
+        else
+        {
+            nYear += nAddYears;
+            if (nYear == 0)
+                nYear = 1;
+        }
+    }
+    else
+    {
+        if (nAddYears > 0)
+        {
+            if (kYearMax - nAddYears < nYear)
+                nYear = kYearMax;
+            else
+                nYear += nAddYears;
+        }
+        else
+        {
+            nYear += nAddYears;
+            if (nYear == 0)
+                nYear = -1;
+        }
+    }
+
+    SetYear( nYear );
+    if (GetMonth() == 2 && GetDay() == 29 && !ImpIsLeapYear( nYear))
+        SetDay(28);
+}
+
+void Date::AddMonths( sal_Int32 nAddMonths )
+{
+    long nMonths = GetMonth() + nAddMonths;
+    long nNewMonth = nMonths % 12;
+    long nYear = GetYear() + nMonths / 12;
+    if( nMonths <= 0 || nNewMonth == 0 )
+        --nYear;
+    if( nNewMonth <= 0 )
+        nNewMonth += 12;
+    if (nYear == 0)
+        nYear = (nAddMonths < 0 ? -1 : 1);
+    else if (nYear < kYearMin)
+        nYear = kYearMin;
+    else if (nYear > kYearMax)
+        nYear = kYearMax;
+    SetMonth( static_cast<sal_uInt16>(nNewMonth) );
+    SetYear( static_cast<sal_Int16>(nYear) );
+    Normalize();
+}
+
 DayOfWeek Date::GetDayOfWeek() const
 {
     return static_cast<DayOfWeek>((GetAsNormalizedDays()-1) % 7);
@@ -209,7 +323,7 @@ sal_uInt16 Date::GetDayOfYear() const
 {
     sal_uInt16 nDay   = GetDay();
     sal_uInt16 nMonth = GetMonth();
-    sal_uInt16 nYear  = GetYear();
+    sal_Int16  nYear  = GetYear();
     Normalize( nDay, nMonth, nYear);
 
     for( sal_uInt16 i = 1; i < nMonth; i++ )
@@ -245,7 +359,7 @@ sal_uInt16 Date::GetWeekOfYear( DayOfWeek eStartDay,
         else if ( nWeek == 53 )
         {
             short nDaysInYear = (short)GetDaysInYear();
-            short nDaysNextYear = (short)Date( 1, 1, GetYear()+1 ).GetDayOfWeek();
+            short nDaysNextYear = (short)Date( 1, 1, GetNextYear() ).GetDayOfWeek();
             nDaysNextYear = (nDaysNextYear+(7-(short)eStartDay)) % 7;
             if ( nDayOfYear > (nDaysInYear-nDaysNextYear-1) )
                 nWeek = 1;
@@ -257,7 +371,7 @@ sal_uInt16 Date::GetWeekOfYear( DayOfWeek eStartDay,
         // First week of a year is equal to the last week of the previous year
         if ( nWeek == 0 )
         {
-            Date aLastDatePrevYear( 31, 12, GetYear()-1 );
+            Date aLastDatePrevYear( 31, 12, GetPrevYear() );
             nWeek = aLastDatePrevYear.GetWeekOfYear( eStartDay, nMinimumNumberOfDaysInWeek );
         }
     }
@@ -273,7 +387,7 @@ sal_uInt16 Date::GetWeekOfYear( DayOfWeek eStartDay,
         else if ( n1WDay == nMinimumNumberOfDaysInWeek + 1 )
         {
             // Year after leapyear
-            if ( Date( 1, 1, GetYear()-1 ).IsLeapYear() )
+            if ( Date( 1, 1, GetPrevYear() ).IsLeapYear() )
                 nWeek = 53;
             else
                 nWeek = 52;
@@ -307,7 +421,7 @@ sal_uInt16 Date::GetDaysInMonth() const
 {
     sal_uInt16 nDay   = GetDay();
     sal_uInt16 nMonth = GetMonth();
-    sal_uInt16 nYear  = GetYear();
+    sal_Int16  nYear  = GetYear();
     Normalize( nDay, nMonth, nYear);
 
     return ImplDaysInMonth( nMonth, nYear );
@@ -315,7 +429,7 @@ sal_uInt16 Date::GetDaysInMonth() const
 
 bool Date::IsLeapYear() const
 {
-    sal_uInt16 nYear = GetYear();
+    sal_Int16 nYear = GetYear();
     return ImpIsLeapYear( nYear );
 }
 
@@ -323,7 +437,7 @@ bool Date::IsValidAndGregorian() const
 {
     sal_uInt16 nDay   = GetDay();
     sal_uInt16 nMonth = GetMonth();
-    sal_uInt16 nYear  = GetYear();
+    sal_Int16  nYear  = GetYear();
 
     if ( !nMonth || (nMonth > 12) )
         return false;
@@ -348,7 +462,7 @@ bool Date::IsValidDate() const
 }
 
 //static
-bool Date::IsValidDate( sal_uInt16 nDay, sal_uInt16 nMonth, sal_uInt16 nYear )
+bool Date::IsValidDate( sal_uInt16 nDay, sal_uInt16 nMonth, sal_Int16 nYear )
 {
     if ( !nMonth || (nMonth > 12) )
         return false;
@@ -361,7 +475,7 @@ bool Date::Normalize()
 {
     sal_uInt16 nDay   = GetDay();
     sal_uInt16 nMonth = GetMonth();
-    sal_uInt16 nYear  = GetYear();
+    sal_Int16  nYear  = GetYear();
 
     if (!Normalize( nDay, nMonth, nYear))
         return false;
@@ -372,7 +486,7 @@ bool Date::Normalize()
 }
 
 //static
-bool Date::Normalize( sal_uInt16 & rDay, sal_uInt16 & rMonth, sal_uInt16 & rYear )
+bool Date::Normalize( sal_uInt16 & rDay, sal_uInt16 & rMonth, sal_Int16 & rYear )
 {
     if (IsValidDate( rDay, rMonth, rYear))
         return false;
@@ -381,42 +495,59 @@ bool Date::Normalize( sal_uInt16 & rDay, sal_uInt16 & rMonth, sal_uInt16 & rYear
     {
         rYear += rMonth / 12;
         rMonth = rMonth % 12;
+        if (rYear == 0)
+            rYear = 1;
     }
-    if (!rMonth)
+    if (rMonth == 0)
     {
-        if (!rYear)
+        --rYear;
+        if (rYear == 0)
+            rYear = -1;
+        rMonth = 12;
+    }
+
+    if (rYear < 0)
+    {
+        sal_uInt16 nDays;
+        while (rDay > (nDays = ImplDaysInMonth( rMonth, rYear)))
         {
-            rYear = 0;
-            rMonth = 1;
-            if (rDay > 31)
-                rDay -= 31;
+            rDay -= nDays;
+            if (rMonth > 1)
+                --rMonth;
             else
-                rDay = 1;
-        }
-        else
-        {
-            --rYear;
-            rMonth = 12;
+            {
+                if (rYear == kYearMin)
+                {
+                    rDay = 1;
+                    rMonth = 1;
+                    return true;
+                }
+                --rYear;
+                rMonth = 12;
+            }
         }
     }
-    sal_uInt16 nDays;
-    while (rDay > (nDays = ImplDaysInMonth( rMonth, rYear)))
+    else
     {
-        rDay -= nDays;
-        if (rMonth < 12)
-            ++rMonth;
-        else
+        sal_uInt16 nDays;
+        while (rDay > (nDays = ImplDaysInMonth( rMonth, rYear)))
         {
-            ++rYear;
-            rMonth = 1;
+            rDay -= nDays;
+            if (rMonth < 12)
+                ++rMonth;
+            else
+            {
+                if (rYear == kYearMax)
+                {
+                    rDay = 31;
+                    rMonth = 12;
+                    return true;
+                }
+                ++rYear;
+                rMonth = 1;
+            }
         }
     }
-    if (rYear > 9999)
-    {
-        rDay = 31;
-        rMonth = 12;
-        rYear = 9999;
-    }
     return true;
 }
 
diff --git a/unotools/source/i18n/localedatawrapper.cxx b/unotools/source/i18n/localedatawrapper.cxx
index 7204f66392bb..6dbd1388ba52 100644
--- a/unotools/source/i18n/localedatawrapper.cxx
+++ b/unotools/source/i18n/localedatawrapper.cxx
@@ -1134,6 +1134,16 @@ static sal_Unicode* ImplAddUNum( sal_Unicode* pBuf, sal_uInt64 nNumber, int nMin
     return pBuf;
 }
 
+static sal_Unicode* ImplAddNum( sal_Unicode* pBuf, sal_Int64 nNumber, int nMinLen )
+{
+    if (nNumber < 0)
+    {
+        *pBuf++ = '-';
+        nNumber = -nNumber;
+    }
+    return ImplAddUNum( pBuf, nNumber, nMinLen);
+}
+
 static sal_Unicode* ImplAdd2UNum( sal_Unicode* pBuf, sal_uInt16 nNumber, bool bLeading )
 {
     DBG_ASSERT( nNumber < 100, "ImplAdd2UNum() - Number >= 100" );
@@ -1324,7 +1334,7 @@ OUString LocaleDataWrapper::getDate( const Date& rDate ) const
     sal_Unicode* pBuf = aBuf;
     sal_uInt16  nDay    = rDate.GetDay();
     sal_uInt16  nMonth  = rDate.GetMonth();
-    sal_uInt16  nYear   = rDate.GetYear();
+    sal_Int16   nYear   = rDate.GetYear();
     sal_uInt16  nYearLen;
 
     if ( true /* IsDateCentury() */ )
@@ -1342,17 +1352,17 @@ OUString LocaleDataWrapper::getDate( const Date& rDate ) const
             pBuf = ImplAddString( pBuf, getDateSep() );
             pBuf = ImplAdd2UNum( pBuf, nMonth, true /* IsDateMonthLeadingZero() */ );
             pBuf = ImplAddString( pBuf, getDateSep() );
-            pBuf = ImplAddUNum( pBuf, nYear, nYearLen );
+            pBuf = ImplAddNum( pBuf, nYear, nYearLen );
         break;
         case MDY :
             pBuf = ImplAdd2UNum( pBuf, nMonth, true /* IsDateMonthLeadingZero() */ );
             pBuf = ImplAddString( pBuf, getDateSep() );
             pBuf = ImplAdd2UNum( pBuf, nDay, true /* IsDateDayLeadingZero() */ );
             pBuf = ImplAddString( pBuf, getDateSep() );
-            pBuf = ImplAddUNum( pBuf, nYear, nYearLen );
+            pBuf = ImplAddNum( pBuf, nYear, nYearLen );
         break;
         default:
-            pBuf = ImplAddUNum( pBuf, nYear, nYearLen );
+            pBuf = ImplAddNum( pBuf, nYear, nYearLen );
             pBuf = ImplAddString( pBuf, getDateSep() );
             pBuf = ImplAdd2UNum( pBuf, nMonth, true /* IsDateMonthLeadingZero() */ );
             pBuf = ImplAddString( pBuf, getDateSep() );
diff --git a/unotools/source/ucbhelper/ucblockbytes.cxx b/unotools/source/ucbhelper/ucblockbytes.cxx
index f894c1cf7e1a..1e88ab7287b4 100644
--- a/unotools/source/ucbhelper/ucblockbytes.cxx
+++ b/unotools/source/ucbhelper/ucblockbytes.cxx
@@ -176,7 +176,7 @@ void SAL_CALL UcbPropertiesChangeListener_Impl::propertiesChange ( const Sequenc
 
                     if (aName.compareToIgnoreAsciiCaseAscii("Expires") == 0)
                     {
-                        DateTime aExpires (0, 0);
+                        DateTime aExpires( DateTime::EMPTY );
                         if (INetMIMEMessage::ParseDateField (aValue, aExpires))
                         {
                             aExpires.ConvertToLocalTime();
diff --git a/vcl/source/control/field2.cxx b/vcl/source/control/field2.cxx
index 7f0e9a8e1135..27b6b41ade8e 100644
--- a/vcl/source/control/field2.cxx
+++ b/vcl/source/control/field2.cxx
@@ -115,6 +115,16 @@ static sal_Unicode* ImplAddNum( sal_Unicode* pBuf, sal_uLong nNumber, int nMinLe
     return pBuf;
 }
 
+static sal_Unicode* ImplAddSNum( sal_Unicode* pBuf, sal_Int32 nNumber, int nMinLen )
+{
+    if (nNumber < 0)
+    {
+        *pBuf++ = '-';
+        nNumber = -nNumber;
+    }
+    return ImplAddNum( pBuf, nNumber, nMinLen);
+}
+
 static sal_uInt16 ImplGetNum( const sal_Unicode*& rpBuf, bool& rbError )
 {
     if ( !*rpBuf )
@@ -1048,7 +1058,7 @@ static bool ImplDateGetValue( const OUString& rStr, Date& rDate, ExtDateFieldFor
         if ( ( nSepPos < 0 ) || ( nSepPos == (aStr.getLength()-1) ) )
         {
             bYear = false;
-            nYear = Date( Date::SYSTEM ).GetYear();
+            nYear = Date( Date::SYSTEM ).GetYearUnsigned();
         }
 
         const sal_Unicode* pBuf = aStr.getStr();
@@ -1114,7 +1124,7 @@ static bool ImplDateGetValue( const OUString& rStr, Date& rDate, ExtDateFieldFor
 
 bool DateFormatter::ImplDateReformat( const OUString& rStr, OUString& rOutStr, const AllSettings& rSettings )
 {
-    Date aDate( 0, 0, 0 );
+    Date aDate( Date::EMPTY );
     if ( !ImplDateGetValue( rStr, aDate, GetExtDateFormat(true), ImplGetLocaleDataWrapper(), GetCalendarWrapper(), GetFieldSettings() ) )
         return true;
 
@@ -1155,7 +1165,7 @@ OUString DateFormatter::ImplGetDateAsText( const Date& rDate,
     {
         // Check if I have to use force showing the century
         sal_uInt16 nTwoDigitYearStart = utl::MiscCfg().GetYear2000();
-        sal_uInt16 nYear = rDate.GetYear();
+        sal_uInt16 nYear = rDate.GetYearUnsigned();
 
         // If year is not in double digit range
         if ( (nYear < nTwoDigitYearStart) || (nYear >= nTwoDigitYearStart+100) )
@@ -1168,7 +1178,7 @@ OUString DateFormatter::ImplGetDateAsText( const Date& rDate,
     OUString aDateSep = ImplGetDateSep( ImplGetLocaleDataWrapper(), GetExtDateFormat( true ) );
     sal_uInt16 nDay = rDate.GetDay();
     sal_uInt16 nMonth = rDate.GetMonth();
-    sal_uInt16 nYear = rDate.GetYear();
+    sal_Int16 nYear = rDate.GetYear();
     sal_uInt16 nYearLen = bShowCentury ? 4 : 2;
 
     if ( !bShowCentury )
@@ -1187,7 +1197,7 @@ OUString DateFormatter::ImplGetDateAsText( const Date& rDate,
             pBuf = ImplAddString( pBuf, aDateSep );
             pBuf = ImplAddNum( pBuf, nMonth, 2 );
             pBuf = ImplAddString( pBuf, aDateSep );
-            pBuf = ImplAddNum( pBuf, nYear, nYearLen );
+            pBuf = ImplAddSNum( pBuf, nYear, nYearLen );
         }
         break;
         case XTDATEF_SHORT_MMDDYY:
@@ -1197,7 +1207,7 @@ OUString DateFormatter::ImplGetDateAsText( const Date& rDate,
             pBuf = ImplAddString( pBuf, aDateSep );
             pBuf = ImplAddNum( pBuf, nDay, 2 );
             pBuf = ImplAddString( pBuf, aDateSep );
-            pBuf = ImplAddNum( pBuf, nYear, nYearLen );
+            pBuf = ImplAddSNum( pBuf, nYear, nYearLen );
         }
         break;
         case XTDATEF_SHORT_YYMMDD:
@@ -1205,7 +1215,7 @@ OUString DateFormatter::ImplGetDateAsText( const Date& rDate,
         case XTDATEF_SHORT_YYMMDD_DIN5008:
         case XTDATEF_SHORT_YYYYMMDD_DIN5008:
         {
-            pBuf = ImplAddNum( pBuf, nYear, nYearLen );
+            pBuf = ImplAddSNum( pBuf, nYear, nYearLen );
             pBuf = ImplAddString( pBuf, aDateSep );
             pBuf = ImplAddNum( pBuf, nMonth, 2 );
             pBuf = ImplAddString( pBuf, aDateSep );
@@ -1227,12 +1237,12 @@ static void ImplDateIncrementDay( Date& rDate, bool bUp )
 
     if ( bUp )
     {
-        if ( (rDate.GetDay() != 31) || (rDate.GetMonth() != 12) || (rDate.GetYear() != 9999) )
+        if ( (rDate.GetDay() != 31) || (rDate.GetMonth() != 12) || (rDate.GetYear() != SAL_MAX_INT16) )
             ++rDate;
     }
     else
     {
-        if ( (rDate.GetDay() != 1 ) || (rDate.GetMonth() != 1) || (rDate.GetYear() != 0) )
+        if ( (rDate.GetDay() != 1 ) || (rDate.GetMonth() != 1) || (rDate.GetYear() != SAL_MIN_INT16) )
             --rDate;
     }
 }
@@ -1242,13 +1252,13 @@ static void ImplDateIncrementMonth( Date& rDate, bool bUp )
     DateFormatter::ExpandCentury( rDate );
 
     sal_uInt16 nMonth = rDate.GetMonth();
-    sal_uInt16 nYear = rDate.GetYear();
+    sal_Int16 nYear = rDate.GetYear();
     if ( bUp )
     {
-        if ( (nMonth == 12) && (nYear < 9999) )
+        if ( (nMonth == 12) && (nYear < SAL_MAX_INT16) )
         {
             rDate.SetMonth( 1 );
-            rDate.SetYear( nYear + 1 );
+            rDate.SetYear( rDate.GetNextYear() );
         }
         else
         {
@@ -1258,10 +1268,10 @@ static void ImplDateIncrementMonth( Date& rDate, bool bUp )
     }
     else
     {
-        if ( (nMonth == 1) && (nYear > 0) )
+        if ( (nMonth == 1) && (nYear > SAL_MIN_INT16) )
         {
             rDate.SetMonth( 12 );
-            rDate.SetYear( nYear - 1 );
+            rDate.SetYear( rDate.GetPrevYear() );
         }
         else
         {
@@ -1279,17 +1289,17 @@ static void ImplDateIncrementYear( Date& rDate, bool bUp )
 {
     DateFormatter::ExpandCentury( rDate );
 
-    sal_uInt16 nYear = rDate.GetYear();
+    sal_Int16 nYear = rDate.GetYear();
     sal_uInt16 nMonth = rDate.GetMonth();
     if ( bUp )
     {
-        if ( nYear < 9999 )
-            rDate.SetYear( nYear + 1 );
+        if ( nYear < SAL_MAX_INT16 )
+            rDate.SetYear( rDate.GetNextYear() );
     }
     else
     {
-        if ( nYear > 0 )
-            rDate.SetYear( nYear - 1 );
+        if ( nYear > SAL_MIN_INT16 )
+            rDate.SetYear( rDate.GetPrevYear() );
     }
     if (nMonth == 2)
     {
@@ -1611,7 +1621,7 @@ void DateFormatter::ImplNewFieldValue( const Date& rDate )
 
 Date DateFormatter::GetDate() const
 {
-    Date aDate( 0, 0, 0 );
+    Date aDate( Date::EMPTY );
 
     if ( GetField() )
     {
@@ -1705,8 +1715,8 @@ void DateFormatter::ExpandCentury( Date& rDate )
 
 void DateFormatter::ExpandCentury( Date& rDate, sal_uInt16 nTwoDigitYearStart )
 {
-    sal_uInt16 nDateYear = rDate.GetYear();
-    if ( nDateYear < 100 )
+    sal_Int16 nDateYear = rDate.GetYear();
+    if ( 0 <= nDateYear && nDateYear < 100 )
     {
         sal_uInt16 nCentury = nTwoDigitYearStart / 100;
         if ( nDateYear < (nTwoDigitYearStart % 100) )
diff --git a/xmloff/source/core/xmluconv.cxx b/xmloff/source/core/xmluconv.cxx
index 1f2fe2446f38..fa34a3006f6b 100644
--- a/xmloff/source/core/xmluconv.cxx
+++ b/xmloff/source/core/xmluconv.cxx
@@ -375,21 +375,29 @@ void SvXMLUnitConverter::convertDateTime( OUStringBuffer& rBuffer,
             aDate += 1;
         }
     }
-    sal_uInt16 nTemp = aDate.GetYear();
-    if (nTemp < 1000)
+    sal_Int16 nTempYear = aDate.GetYear();
+    assert(nTempYear != 0);
+    if (nTempYear < 0)
+    {
+        rBuffer.append( '-');
+        nTempYear = -nTempYear;
+    }
+    if (nTempYear < 1000)
         rBuffer.append( '0');
-    if (nTemp < 100)
+    if (nTempYear < 100)
         rBuffer.append( '0');
-    if (nTemp < 10)
+    if (nTempYear < 10)
         rBuffer.append( '0');
-    rBuffer.append( sal_Int32( nTemp));
+    rBuffer.append( sal_Int32( nTempYear));
     rBuffer.append( '-');
-    nTemp = aDate.GetMonth();
+    sal_uInt16 nTemp = aDate.GetMonth();
+    assert(1 <= nTemp && nTemp <= 12);
     if (nTemp < 10)
         rBuffer.append( '0');
     rBuffer.append( sal_Int32( nTemp));
     rBuffer.append( '-');
     nTemp = aDate.GetDay();
+    assert(1 <= nTemp && nTemp <= 31);
     if (nTemp < 10)
         rBuffer.append( '0');
     rBuffer.append( sal_Int32( nTemp));
diff --git a/xmloff/source/text/txtlists.cxx b/xmloff/source/text/txtlists.cxx
index 3fd31e514b4b..09c62c7f742c 100644
--- a/xmloff/source/text/txtlists.cxx
+++ b/xmloff/source/text/txtlists.cxx
@@ -225,7 +225,7 @@ OUString XMLTextListsHelper::GenerateNewListId() const
     {
         // Value of xml:id in element <text:list> has to be a valid ID type (#i92478#)
         sal_Int64 n = ::tools::Time( ::tools::Time::SYSTEM ).GetTime();
-        n += Date( Date::SYSTEM ).GetDate();
+        n += Date( Date::SYSTEM ).GetDateUnsigned();
         n += comphelper::rng::uniform_int_distribution(0, std::numeric_limits<int>::max());
         // Value of xml:id in element <text:list> has to be a valid ID type (#i92478#)
         sTmpStr += OUString::number( n );
diff --git a/xmlscript/source/xmldlg_imexp/xmldlg_export.cxx b/xmlscript/source/xmldlg_imexp/xmldlg_export.cxx
index 1732d64523de..b352053c8ee6 100644
--- a/xmlscript/source/xmldlg_imexp/xmldlg_export.cxx
+++ b/xmlscript/source/xmldlg_imexp/xmldlg_export.cxx
@@ -591,7 +591,7 @@ void ElementDescriptor::readDateAttr( OUString const & rPropName, OUString const
             if (a >>= aUDate)
             {
                 ::Date aTDate(aUDate);
-                addAttribute( rAttrName, OUString::number( aTDate.GetDate() ) );
+                addAttribute( rAttrName, OUString::number( static_cast<sal_Int32>(aTDate.GetDate()) ) );
             }
             else
                 OSL_FAIL( "### internal error" );
diff --git a/xmlsecurity/source/dialogs/certificateviewer.cxx b/xmlsecurity/source/dialogs/certificateviewer.cxx
index 509a467fbf4d..a2b61370e86b 100644
--- a/xmlsecurity/source/dialogs/certificateviewer.cxx
+++ b/xmlsecurity/source/dialogs/certificateviewer.cxx
@@ -129,8 +129,8 @@ CertificateViewerGeneralTP::CertificateViewerGeneralTP( vcl::Window* _pParent, C
     utl::typeConvert( xCert->getNotValidBefore(), aDateTimeStart );
     utl::typeConvert( xCert->getNotValidAfter(), aDateTimeEnd );
 
-    OUString sValidFromDate = GetSettings().GetUILocaleDataWrapper().getDate( aDateTimeStart.GetDate() );
-    OUString sValidToDate = GetSettings().GetUILocaleDataWrapper().getDate( aDateTimeEnd.GetDate() );
+    OUString sValidFromDate = GetSettings().GetUILocaleDataWrapper().getDate( Date( aDateTimeStart.GetDate()));
+    OUString sValidToDate = GetSettings().GetUILocaleDataWrapper().getDate( Date( aDateTimeEnd.GetDate()));
 
     m_pValidFromDateFI->SetText(sValidFromDate);
     m_pValidToDateFI->SetText(sValidToDate);
@@ -253,12 +253,12 @@ CertificateViewerDetailsTP::CertificateViewerDetailsTP( vcl::Window* _pParent, C
 
     DateTime aDateTime( DateTime::EMPTY );
     utl::typeConvert( xCert->getNotValidBefore(), aDateTime );
-    aLBEntry = GetSettings().GetUILocaleDataWrapper().getDate( aDateTime.GetDate() );
+    aLBEntry = GetSettings().GetUILocaleDataWrapper().getDate( Date( aDateTime.GetDate()) );
     aLBEntry += " ";
     aLBEntry += GetSettings().GetUILocaleDataWrapper().getTime( aDateTime.GetTime() );
     InsertElement( XMLSEC_RES( STR_VALIDFROM ), aLBEntry, aLBEntry  );
     utl::typeConvert( xCert->getNotValidAfter(), aDateTime );
-    aLBEntry = GetSettings().GetUILocaleDataWrapper().getDate( aDateTime.GetDate() );
+    aLBEntry = GetSettings().GetUILocaleDataWrapper().getDate( Date( aDateTime.GetDate()) );
     aLBEntry += " ";
     aLBEntry += GetSettings().GetUILocaleDataWrapper().getTime( aDateTime.GetTime() );
     InsertElement( XMLSEC_RES( STR_VALIDTO ), aLBEntry, aLBEntry );