fpspreadsheet: Remove fix for Excel's Year-1900 problem because it creates new issues... (issue #38742).

git-svn-id: https://svn.code.sf.net/p/lazarus-ccr/svn@8033 8e941d3f-bd1b-0410-a28a-d453659cc2b4

components/fpspreadsheet/source/common/xlscommon.pas

@@ -821,29 +821,17 @@ begin
   if (AExcelDateNum < 1) and (AExcelDateNum >= 0)  then
   begin
     Result := AExcelDateNum;
-  end
-  else
+  end else
   begin
     case ADateMode of
       dm1900:
         begin
           Result := AExcelDateNum + DATEMODE_1900_BASE - 1.0;
-          // Excel and Lotus 1-2-3 incorrectly assume that 1900 was a leap year
-          // Therefore all dates before March 01 are off by 1.
-          // The old fps implementation corrected only Feb 29, but all days are
-          // wrong!
-          if AExcelDateNum < 61 then
-            Result := Result + 1.0;
-            (*
-
-          // Check for Lotus 1-2-3 bug with 1900 leap year
-          if AExcelDateNum=61.0 then
-            // 29 feb does not exist, change to 28
-            // Spell out that we remove a day for ehm "clarity".
-            result := 61.0 - 1.0 + DATEMODE_1900_BASE - 1.0
-          else
-            result := AExcelDateNum + DATEMODE_1900_BASE - 1.0;
-          *)
+          { Excel and Lotus 1-2-3 incorrectly assume that 1900 was a leap year
+            Therefore all dates before March 01 are off by 1.
+            Unlike earlier fps versions we no longer attempt to fix this issue
+            because it leads to other issues (when dates are in order then
+            the weekdays are off by 1!) }
         end;
       dm1904:
         result := AExcelDateNum + DATEMODE_1904_BASE;
@@ -857,17 +845,21 @@ function ConvertDateTimeToExcelDateTime(const ADateTime: TDateTime;
   ADateMode: TDateMode): Double;
 begin
   // Time only
-  if (ADateTime<1) and (ADateTime>=0) then
+  if (ADateTime < 1) and (ADateTime >= 0) then
   begin
-    Result:=ADateTime;
+    Result := ADateTime;
   end
   else
   begin
     case ADateMode of
     dm1900:
       begin
+        { Excel and Lotus 1-2-3 incorrectly assume that 1900 was a leap year
+          Therefore all dates before March 01 are off by 1.
+          Unlike earlier fps versions we no longer attempt to fix this issue
+          because it leads to other issues (when dates are in order then
+          the weekdays are off by 1!) }
         Result := ADateTime - DATEMODE_1900_BASE + 1.0;
-        if Result < 61 then Result := Result - 1.0;
       end;
     dm1904:
       Result := ADateTime - DATEMODE_1904_BASE;
@@ -1507,7 +1499,9 @@ begin
 end;
 
 {@@ ----------------------------------------------------------------------------
-  Converts the number to a date/time and return that if it is
+  Converts the number to a date/time and returns that if it is
+  Like LibreOffice Calc, we do not attempt to fix the Year-1900 issue of Excel
+  files because it leads to even more confusion...
 -------------------------------------------------------------------------------}
 function TsSpreadBIFFReader.IsDateTime(Number: Double;
   ANumberFormat: TsNumberFormat; ANumberFormatStr: String;
@@ -2250,7 +2244,7 @@ begin
   end else
     cell := sheet.AddCell(ARow, ACol);  // "real" cell
 
-  if IsDateTime(value, nf, nfs, dt) then   // Year-1900 correction occurs here!
+  if IsDateTime(value, nf, nfs, dt) then   // DateMode correction occurs here!
     sheet.WriteDateTime(cell, dt, nf, nfs)
   else if nf = nfText then
     sheet.WriteText(cell, GeneralFormatFloat(value, FWorkbook.FormatSettings))
@@ -4189,11 +4183,11 @@ var
   cf: TsCellFormat;
   nfp: TsNumFormatParams;
 begin
-  // We must correct the bug of Lotus 1-2-3 which had ignored that year 1900 was
-  // a leap year, but only for "normal" date format, not for time-interval formats
+  // We must convert the date value to the Excel date basis (DateMode),
+  // but not for time-interval formats.
   cf := TsWorksheet(FWorksheet).ReadCellFormat(ACell);
   nfp := TsWorkbook(FWorkbook).GetNumberFormat(cf.NumberFormatIndex);
-  if IsTimeIntervalFormat(nfp) then //or IsTimeFormat(nfp) then
+  if IsTimeIntervalFormat(nfp) then
     ExcelDateSerial := AValue
   else
     ExcelDateSerial := ConvertDateTimeToExcelDateTime(AValue, FDateMode);

components/fpspreadsheet/source/common/xlsxml.pas

@@ -2745,6 +2745,7 @@ var
   fmt: PsCellFormat;
 begin
   Unused(ARow, ACol);
+  (*
   fmt := (FWorkbook as TsWorkbook).GetPointerToCellFormat(ACell^.FormatIndex);
   if (fmt <> nil) and (uffNumberFormat in fmt^.UsedFormattingFields) then
   begin
@@ -2764,9 +2765,10 @@ begin
   end;
   if valueStr = '' then
   begin
+  *)
     ExcelDate := ConvertDateTimeToExcelDateTime(AValue, FDateMode);
     valueStr := FormatDateTime('yyyy-mm-dd"T"hh:nn:ss.zzz', ExcelDate);
-  end;
+  //end;
 
   AppendToStream(AStream, Format(CELL_INDENT +
     '<Cell%s%s%s%s%s>' + LF + VALUE_INDENT + // colIndex, style, formula, hyperlink, merge

components/fpspreadsheet/source/common/xlsxooxml.pas

@@ -1043,7 +1043,8 @@ begin
       begin
         if IsDateTimeFormat(numFmt) then
         begin
-          if not IsTimeIntervalFormat(numFmt) then   // no correction of time origin for "time interval" format
+          if not IsTimeIntervalFormat(numFmt) then
+            // no correction of time origin for "time" or "time interval" format
             number := ConvertExcelDateTimeToDateTime(number, FDateMode);
           sheet.WriteDateTime(cell, number);
         end