+wxDateSpan wxDateTime::DiffAsDateSpan(const wxDateTime& dt) const
+{
+ wxASSERT_MSG( IsValid() && dt.IsValid(), wxT("invalid wxDateTime"));
+
+ // If dt is larger than this, calculations below needs to be inverted.
+ int inv = 1;
+ if ( dt > *this )
+ inv = -1;
+
+ int y = GetYear() - dt.GetYear();
+
+ // If month diff is negative, dt is the year before, so decrease year
+ // and set month diff to its inverse, e.g. January - December should be 1,
+ // not -11.
+ int m = GetMonth() - dt.GetMonth();
+ if ( m * inv < 0 )
+ {
+ m += inv * MONTHS_IN_YEAR;
+ y -= inv;
+ }
+
+ // Same logic for days as for months above. Use number of days in month
+ // from the month which end date we're crossing.
+ int d = GetDay() - dt.GetDay();
+ if ( d * inv < 0 )
+ {
+ d += inv * wxDateTime::GetNumberOfDays(
+ inv > 0 ? dt.GetMonth() : GetMonth(),
+ inv > 0 ? dt.GetYear() : GetMonth());
+ m -= inv;
+ }
+
+ int w = d / DAYS_PER_WEEK;
+
+ // Remove weeks from d, since wxDateSpan only keep days as the ones
+ // not in complete weeks
+ d -= w * DAYS_PER_WEEK;
+
+ return wxDateSpan(y, m, w, d);
+}
+