bool UnitMgr::doConversion(double           fromValue,
                           double           fromScale,
                           UnitDefPtr       fromUnitDef, 
                           double&          toValue,
                           double           toScale,
                           UnitDefPtr       toUnitDef,
                           const Date_Time& when,
                           bool             whenIsValid) const
{
   // The key to understanding this method: the conversion factor
   // associated with a unit is for converting from that unit to the
   // standard unit for that type.  When the unit is "per month", this
   // conversion factor assumes a 31 day month, and when the unit is
   // "per year", this conversion factor assumes a 365 day year.

   int daysIn (0);               // days in month or year

   // Debug Support
   if (whenIsValid && (when.get_year() == 2016))
   {
      static int diagCnt (0);
      ++diagCnt; // debug breakpoint
   }

   // Get the factor for converting to standard units and correct it
   // for the actual length of the month or year.
   double coeffToStd( fromUnitDef->getFactor() );

   if (fromUnitDef->isPerMonth() && whenIsValid &&
       (daysIn = when.daysInMonth()) != 31)
   {
       coeffToStd *= double(daysIn) / double(31);
   }
   else if (fromUnitDef->isPerYear() && whenIsValid &&
            (daysIn = when.daysInYear()) != 365)
   {
       coeffToStd *= double(daysIn) / double(365);
   }

   // Convert the given value to an intermediate value in standard units.
   double stdValue( ( fromValue / coeffToStd ) * fromScale );

   // Get the factor for converting from standard units and correct it
   // for the actual length of the month or year.
   double coeffFromStd( toUnitDef->getFactor() );

   if (toUnitDef->isPerMonth() && whenIsValid &&
       (daysIn = when.daysInMonth()) != 31)
   {
       coeffFromStd *= double(daysIn) / double(31);
   }
   else if (toUnitDef->isPerYear() && whenIsValid &&
            (daysIn = when.daysInYear()) != 365)
   {
       coeffFromStd *= double(daysIn) / double(365);
   }

   // Convert the intermediate value to the desired units and scale.
   toValue = stdValue * coeffFromStd / toScale;

   return false; // success
}
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