Encapsulate the horrid gas encoding in gas change events

We should never pass permille values around as integers. And we shouldn't
have to decode the stupid value in more than one place.

This doesn't tackle all the places where we access O2 and He "too early"
and should instead keep passing around a gaxmix. But it's a first step.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

dive.c

@@ -6,6 +6,7 @@
 #include <limits.h>
 #include "gettext.h"
 #include "dive.h"
+#include "libdivecomputer.h"
 
 struct tag_entry *g_tag_list = NULL;
 
@@ -76,6 +77,19 @@ void remove_event(struct event* event)
 	}
 }
 
+/* this returns a pointer to static variable - so use it right away after calling */
+struct gasmix *get_gasmix_from_event(struct event *ev)
+{
+	static struct gasmix g;
+	g.o2.permille = g.he.permille = 0;
+	if (ev && (ev->type == SAMPLE_EVENT_GASCHANGE || ev->type == SAMPLE_EVENT_GASCHANGE2)) {
+		g.o2.permille = 10 * ev->value & 0xffff;
+		if (ev->type == SAMPLE_EVENT_GASCHANGE2)
+			g.he.permille = 10 * (ev->value >> 16);
+	}
+	return &g;
+}
+
 int get_pressure_units(int mb, const char **units)
 {
 	int pressure;

dive.h

@@ -69,6 +69,18 @@ typedef struct
 	const char *description; /* "integrated", "belt", "ankle" */
 } weightsystem_t;
 
+/*
+ * Events are currently based straight on what libdivecomputer gives us.
+ *  We need to wrap these into our own events at some point to remove some of the limitations.
+ */
+struct event {
+	struct event *next;
+	duration_t time;
+	int type, flags, value;
+	bool deleted;
+	char name[];
+};
+
 extern int get_pressure_units(int mb, const char **units);
 extern double get_depth_units(int mm, int *frac, const char **units);
 extern double get_volume_units(unsigned int ml, int *frac, const char **units);
@@ -94,6 +106,7 @@ static inline int get_he(const struct gasmix *mix)
 
 extern void sanitize_gasmix(struct gasmix *mix);
 extern int gasmix_distance(const struct gasmix *a, const struct gasmix *b);
+extern struct gasmix *get_gasmix_from_event(struct event *ev);
 
 static inline bool is_air(int o2, int he)
 {
@@ -167,22 +180,6 @@ int taglist_get_tagstring(struct tag_entry *tag_list, char *buffer, int len);
 void taglist_init_global();
 void taglist_free(struct tag_entry *tag_list);
 
-/*
- * Events are currently pretty meaningless. This is
- * just based on the random data that libdivecomputer
- * gives us. I'm not sure what a real "architected"
- * event model would actually look like, but right
- * now you can associate a list of events with a dive,
- * and we'll do something about it.
- */
-struct event {
-	struct event *next;
-	duration_t time;
-	int type, flags, value;
-	bool deleted;
-	char name[];
-};
-
 /*
  * NOTE! The deviceid and diveid are model-specific *hashes* of
  * whatever device identification that model may have. Different

divelist.c

@@ -160,7 +160,7 @@ static int active_o2(struct dive *dive, struct divecomputer *dc, duration_t time
 			break;
 		if (strcmp(event->name, "gaschange"))
 			continue;
-		o2permille = 10 * (event->value & 0xffff);
+		o2permille = get_o2(get_gasmix_from_event(event));
 	}
 	return o2permille;
 }

planner.c

@@ -78,8 +78,9 @@ void get_gas_from_events(struct divecomputer *dc, int time, int *o2, int *he)
 	struct event *event = dc->events;
 	while (event && event->time.seconds <= time) {
 		if (!strcmp(event->name, "gaschange")) {
-			*o2 = 10 * event->value & 0xffff;
-			*he = 10 * event->value >> 16;
+			struct gasmix *g = get_gasmix_from_event(event);
+			*o2 = get_o2(g);
+			*he = get_he(g);
 		}
 		event = event->next;
 	}

profile.c

@@ -578,13 +578,15 @@ int get_cylinder_index(struct dive *dive, struct event *ev)
 	int i;
 	int best = 0, score = INT_MAX;
 	int target_o2, target_he;
+	struct gasmix *g;
 
 	/*
 	 * Crazy gas change events give us odd encoded o2/he in percent.
 	 * Decode into our internal permille format.
 	 */
-	target_o2 = (ev->value & 0xFFFF) * 10;
-	target_he = (ev->value >> 16) * 10;
+	g = get_gasmix_from_event(ev);
+	target_o2 = get_o2(g);
+	target_he = get_he(g);
 
 	/*
 	 * Try to find a cylinder that best matches the target gas

qt-ui/profile/diveeventitem.cpp

@@ -82,8 +82,9 @@ void DiveEventItem::setupToolTipString()
 	int type = internalEvent->type;
 	if (value) {
 		if (type == SAMPLE_EVENT_GASCHANGE || type == SAMPLE_EVENT_GASCHANGE2) {
-			int he = value >> 16;
-			int o2 = value & 0xffff;
+			struct gasmix *g = get_gasmix_from_event(internalEvent);
+			int he = get_he(g);
+			int o2 = get_o2(g);
 
 			name += ": ";
 			if (he)