1 files changed, 25 insertions, 0 deletions
diff --git a/equipment.c b/equipment.c
index b69155629..a67df68a4 100644
--- a/equipment.c
+++ b/equipment.c
@@ -72,6 +72,31 @@ bool cylinder_none(void *_data)
 	return cylinder_nodata(cyl) && cylinder_nosamples(cyl);
 }
 
+/* look at all dive computers and figure out if this cylinder is used anywhere
+ * d has to be a valid dive (test before calling)
+ * cyl does not have to be a cylinder that is part of this dive structure */
+bool cylinder_is_used(struct dive *d, cylinder_t *cyl)
+{
+	struct divecomputer *dc = &d->dc;
+	bool same_as_first = gasmix_distance(&cyl->gasmix, &d->cylinder[0].gasmix) < 200;
+	while (dc) {
+		struct event *ev = get_next_event(dc->events, "gaschange");
+		if (same_as_first && (!ev || ev->time.seconds > 30)) {
+			// unless there is a gas change in the first 30 seconds we can
+			// always mark the first cylinder as used
+			return true;
+		}
+		while (ev) {
+			if (gasmix_distance(&cyl->gasmix, get_gasmix_from_event(ev)) < 200)
+				return true;
+
+			ev = get_next_event(ev->next, "gaschange");
+		}
+		dc = dc->next;
+	}
+	return false;
+}
+
 bool weightsystem_none(void *_data)
 {
 	weightsystem_t *ws = _data;