Fix recurrence rule expansion with ordered weekday

When the order of a weekday in BYDAY rule expansion (like -5SA or 5SU
for monthly or 55WE for yearly) exceeds the number of available weekdays
in the period (month or year), rule expansion with negative order could
result in a floating point exception. The reason: the modified frequency
might become zero.

Solution. Check order against number of available weekdays and terminate
expansion early whenever possible (also for positive orders).

Signed-off-by: Lars Henriksen <LarsHenriksen@get2net.dk>
Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

3 files changed, 57 insertions, 20 deletions

diff --git a/src/recur.c b/src/recur.c
index 997fb15..647ba11 100644
--- a/src/recur.c
+++ b/src/recur.c
@@ -1173,7 +1173,7 @@ static int expand_monthly(time_t start, long dur, struct rpt *rpt, llist_t *exc,
 		LLIST_FOREACH(&rpt->bywday, i) {
 			w = LLIST_GET_DATA(i);
 
-			int order, wday;
+			int order, wday, nbwd;
 
 			localtime_r(&start, &tm_start);
 			/*
@@ -1188,6 +1188,11 @@ static int expand_monthly(time_t start, long dur, struct rpt *rpt, llist_t *exc,
 				 */
 				order = *w / WEEKINDAYS;
 				wday = *w % WEEKINDAYS;
+				nbwd = wday_per_month(tm_day.tm_mon + 1,
+						      tm_day.tm_year + 1900,
+						      wday);
+				if (nbwd < order)
+					return 0;
 				r.freq = order;
 				tm_start.tm_mday = 1;
 				tm_start.tm_mon = tm_day.tm_mon;
@@ -1218,11 +1223,12 @@ static int expand_monthly(time_t start, long dur, struct rpt *rpt, llist_t *exc,
 				 */
 				order = -(*w) / WEEKINDAYS;
 				wday = -(*w) % WEEKINDAYS;
-				r.freq = wday_per_month(
-						tm_day.tm_mon + 1,
-						tm_day.tm_year + 1900,
-						wday
-					 ) - order + 1;
+				nbwd = wday_per_month(tm_day.tm_mon + 1,
+						      tm_day.tm_year + 1900,
+						      wday);
+				if (nbwd < order)
+					return 0;
+				r.freq = nbwd - order + 1;
 				tm_start.tm_mday = 1;
 				tm_start.tm_mon = tm_day.tm_mon;
 				tm_start.tm_year = tm_day.tm_year;
@@ -1259,7 +1265,7 @@ static int expand_yearly(time_t start, long dur, struct rpt *rpt, llist_t *exc,
 {
 	struct tm tm_start, tm_day;
 	llist_item_t *i, *j;
-	int *m, *w, mday, wday, order;
+	int *m, *w, mday, wday, order, nbwd;
 	time_t nstart;
 	struct rpt r;
 
@@ -1312,6 +1318,19 @@ static int expand_yearly(time_t start, long dur, struct rpt *rpt, llist_t *exc,
 				 */
 				order = *w / WEEKINDAYS;
 				wday = *w % WEEKINDAYS;
+				if (rpt->bymonth.head)
+					nbwd = wday_per_month(
+						tm_day.tm_mon + 1,
+						tm_day.tm_year + 1900,
+						wday
+					       );
+				else
+					nbwd = wday_per_year(
+						tm_day.tm_year + 1900,
+						wday
+					       );
+				if (nbwd < order)
+					return 0;
 				r.freq = order;
 				tm_start.tm_mday = 1;
 				if (rpt->bymonth.head)
@@ -1344,21 +1363,25 @@ static int expand_yearly(time_t start, long dur, struct rpt *rpt, llist_t *exc,
 				 */
 				order = -(*w) / WEEKINDAYS;
 				wday = -(*w) % WEEKINDAYS;
-				if (rpt->bymonth.head) {
-					r.freq = wday_per_month(
-							tm_day.tm_mon + 1,
-							tm_day.tm_year + 1900,
-							wday
-						 ) - order + 1;
+				if (rpt->bymonth.head)
+					nbwd = wday_per_month(
+						tm_day.tm_mon + 1,
+						tm_day.tm_year + 1900,
+						wday
+					       );
+				else
+					nbwd = wday_per_year(
+						tm_day.tm_year + 1900,
+						wday
+					       );
+				if (nbwd < order)
+					return 0;
+				r.freq = nbwd - order + 1;
+				tm_start.tm_mday = 1;
+				if (rpt->bymonth.head)
 					tm_start.tm_mon = tm_day.tm_mon;
-				} else {
-					r.freq = wday_per_year(
-							tm_day.tm_year + 1900,
-							wday
-						 ) - order + 1;
+				else
 					tm_start.tm_mon = 0;
-				}
-				tm_start.tm_mday = 1;
 				tm_start.tm_year = tm_day.tm_year;
 				tm_start.tm_isdst = -1;
 				nstart = date_sec_change(
diff --git a/test/data/rfc5545 b/test/data/rfc5545
index 421dd53..d9863ce 100644
--- a/test/data/rfc5545
+++ b/test/data/rfc5545
@@ -25,3 +25,4 @@
 12/25/1997 [1] {3Y w-11} Last Thursday of the year every third year, forever (FREQ=YEARLY;INTERVAL=3;BYDAY=-1TH)
 06/22/1997 [1] {2Y w0 w1} Every Sunday and Monday, every other year (FREQ=YEARLY;INTERVAL=2;BYDAY=SU,MO)
 02/01/1997 [1] {1Y -> 01/31/2005 d1 d29 m2} Every year on February 1 and 29 for eight years (RRULE:FREQ=YEARLY;UNTIL=20050131T000000Z;BYMONTH=2;BYMONTHDAY=1,29)
+08/01/2020 @ 08:41 -> 08/01/2020 @ 10:11 {1M w-41} |negative ordered weekday may not exist
diff --git a/test/recur-009.sh b/test/recur-009.sh
index 6ee302d..2558b4c 100755
--- a/test/recur-009.sh
+++ b/test/recur-009.sh
@@ -6,6 +6,13 @@
 if [ "$1" = 'actual' ]; then
   "$CALCURSE" --read-only -D "$DATA_DIR"/ -c "$DATA_DIR/rfc5545" \
   -Q --from 1/1/1996 --to 12/31/2007 --filter-type recur
+  echo ""
+  echo "Floating point exception?"
+  "$CALCURSE" --read-only -D "$DATA_DIR"/ -c "$DATA_DIR/rfc5545" \
+  -Q --day 8/1/2020 --filter-type recur &&
+  "$CALCURSE" --read-only -D "$DATA_DIR"/ -c "$DATA_DIR/rfc5545" \
+  -Q --day 11/1/2020 --filter-type recur &&
+  echo "No Floating point exception on November 1, 2020"
 elif [ "$1" = 'expected' ]; then
   cat <<EOD
 11/05/96:
@@ -5323,6 +5330,12 @@ elif [ "$1" = 'expected' ]; then
 
 12/31/07:
  * Every Sunday and Monday, every other year (FREQ=YEARLY;INTERVAL=2;BYDAY=SU,MO)
+
+Floating point exception?
+08/01/20:
+ - 08:41 -> 10:11
+	negative ordered weekday may not exist
+No Floating point exception on November 1, 2020
 EOD
 else
   ./run-test "$0"