Add utility to calculate date range in seconds on Chrono library.

source/Library/Chrono.cpp

@@ -219,6 +219,40 @@ Date Chrono::ReverseDayOfyear(Uint16 year, Uint16 doy)
     return Date(year, month, doy);
 }
 
+// ------------------------------------------------------------------------------------------------
+Int64 Chrono::DateRangeToSeconds(Uint16 _year, Uint8 _month, Uint8 _day, Uint16 year_, Uint8 month_, Uint8 day_)
+{
+    // Are we within the same year?
+    if (_year == year_)
+    {
+        return (DayOfYear(_year, _month, _day) - DayOfYear(year_, month_, day_)) * 86400ULL;
+    }
+    // Should we negate the result when returning it?
+    bool neg = false;
+    // Is the start year greater than the end year?
+    if (_year > year_)
+    {
+        std::swap(_year, year_);
+        std::swap(_month, month_);
+        std::swap(_day, day_);
+        // Negate the result
+        neg = true;
+    }
+    // Calculate the remaining days from the first year
+    Int64 num = DaysInYear(_year) - DayOfYear(_year, _month, _day);
+    // Calculate the days withing the years range
+    while (++_year < year_)
+    {
+        num += DaysInYear(_year);
+    }
+    // Calculate the days up to the last day
+    num += DayOfYear(year_, month_, day_);
+    // Convert the obtained days in seconds
+    num *= 86400ULL;
+    // Return the result
+    return neg ? -num : num;
+}
+
 // ------------------------------------------------------------------------------------------------
 static SLongInt SqGetEpochTimeMicro()
 {

source/Library/Chrono.hpp

@@ -104,6 +104,11 @@ public:
      * Convert just the year and day of year to full date.
     */
     static Date ReverseDayOfyear(Uint16 year, Uint16 doy);
+
+    /* --------------------------------------------------------------------------------------------
+     * Calculate the number of days in the specified date range.
+    */
+    static Int64 DateRangeToSeconds(Uint16 _year, Uint8 _month, Uint8 _day, Uint16 year_, Uint8 month_, Uint8 day_);
 };
 
 } // Namespace:: SqMod