Start sanitizing gaschange event information

Decode the gasmix data into a sane format when creating the event, and
add the (currently unused) ability to specify a gas change to a
particular cylinder rather than (or in addition to) the gasmix.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

8 files changed, 234 insertions, 97 deletions

diff --git a/dive.c b/dive.c
index 9972212aa..e7bf685e6 100644
--- a/dive.c
+++ b/dive.c
@@ -26,7 +26,31 @@ static const char *default_tags[] = {
 	QT_TRANSLATE_NOOP("gettextFromC", "deco")
 };
 
-void add_event(struct divecomputer *dc, int time, int type, int flags, int value, const char *name)
+int event_is_gaschange(struct event *ev)
+{
+	return ev->type == SAMPLE_EVENT_GASCHANGE ||
+		ev->type == SAMPLE_EVENT_GASCHANGE2;
+}
+
+/*
+ * Does the gas mix data match the legacy
+ * libdivecomputer event format? If so,
+ * we can skip saving it, in order to maintain
+ * the old save formats. We'll re-generate the
+ * gas mix when loading.
+ */
+int event_gasmix_redundant(struct event *ev)
+{
+	int value = ev->value;
+	int o2, he;
+
+	o2 = (value & 0xffff) * 10;
+	he = (value >> 16) * 10;
+	return	o2 == ev->gas.mix.o2.permille &&
+		he == ev->gas.mix.he.permille;
+}
+
+struct event *add_event(struct divecomputer *dc, int time, int type, int flags, int value, const char *name)
 {
 	struct event *ev, **p;
 	unsigned int size, len = strlen(name);
@@ -34,7 +58,7 @@ void add_event(struct divecomputer *dc, int time, int type, int flags, int value
 	size = sizeof(*ev) + len + 1;
 	ev = malloc(size);
 	if (!ev)
-		return;
+		return NULL;
 	memset(ev, 0, size);
 	memcpy(ev->name, name, len);
 	ev->time.seconds = time;
@@ -42,6 +66,22 @@ void add_event(struct divecomputer *dc, int time, int type, int flags, int value
 	ev->flags = flags;
 	ev->value = value;
 
+	/*
+	 * Expand the events into a sane format. Currently
+	 * just gas switches
+	 */
+	switch (type) {
+	case SAMPLE_EVENT_GASCHANGE2:
+		/* High 16 bits are He percentage */
+		ev->gas.mix.he.permille = (value >> 16) * 10;
+	/* Fallthrough */
+	case SAMPLE_EVENT_GASCHANGE:
+		/* Low 16 bits are O2 percentage */
+		ev->gas.mix.o2.permille = (value & 0xffff) * 10;
+		ev->gas.index = -1;
+		break;
+	}
+
 	p = &dc->events;
 
 	/* insert in the sorted list of events */
@@ -50,6 +90,7 @@ void add_event(struct divecomputer *dc, int time, int type, int flags, int value
 	ev->next = *p;
 	*p = ev;
 	remember_event(name);
+	return ev;
 }
 
 static int same_event(struct event *a, struct event *b)
@@ -107,14 +148,11 @@ void update_event_name(struct dive *d, struct event *event, char *name)
 /* 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;
+	static struct gasmix dummy;
+	if (ev && event_is_gaschange(ev))
+		return &ev->gas.mix;
+
+	return &dummy;
 }
 
 int get_pressure_units(int mb, const char **units)
@@ -1543,6 +1581,7 @@ static void add_initial_gaschange(struct dive *dive, struct divecomputer *dc)
 static void dc_cylinder_renumber(struct dive *dive, struct divecomputer *dc, int mapping[])
 {
 	int i;
+	struct event *ev;
 
 	/* Did the first gas get remapped? Add gas switch event */
 	if (mapping[0] > 0)
@@ -1559,6 +1598,15 @@ static void dc_cylinder_renumber(struct dive *dive, struct divecomputer *dc, int
 		if (sensor >= 0)
 			s->sensor = sensor;
 	}
+
+	/* Remap the gas change indexes */
+	for (ev = dc->events; ev; ev = ev->next) {
+		if (!event_is_gaschange(ev))
+			continue;
+		if (ev->gas.index < 0)
+			continue;
+		ev->gas.index = mapping[ev->gas.index];
+	}
 }
 
 /*
diff --git a/dive.h b/dive.h
index eb8909118..55396d8fe 100644
--- a/dive.h
+++ b/dive.h
@@ -85,11 +85,29 @@ typedef struct
 struct event {
 	struct event *next;
 	duration_t time;
-	int type, flags, value;
+	int type;
+	/* This is the annoying libdivecomputer format. */
+	int flags, value;
+	/* .. and this is our "extended" data for some event types */
+	union {
+		/*
+		 * Currently only for gas switch events.
+		 *
+		 * NOTE! The index may be -1, which means "unknown". In that
+		 * case, the get_cylinder_index() function will give the best
+		 * match with the cylinders in the dive based on gasmix.
+		 */
+		struct {
+			int index;
+			struct gasmix mix;
+		} gas;
+	};
 	bool deleted;
 	char name[];
 };
 
+extern int event_is_gaschange(struct event *ev);
+extern int event_gasmix_redundant(struct event *ev);
 
 extern int get_pressure_units(int mb, const char **units);
 extern double get_depth_units(int mm, int *frac, const char **units);
@@ -651,7 +669,7 @@ extern void copy_samples(struct divecomputer *s, struct divecomputer *d);
 extern bool is_cylinder_used(struct dive *dive, int idx);
 extern void fill_default_cylinder(cylinder_t *cyl);
 extern void add_gas_switch_event(struct dive *dive, struct divecomputer *dc, int time, int idx);
-extern void add_event(struct divecomputer *dc, int time, int type, int flags, int value, const char *name);
+extern struct event *add_event(struct divecomputer *dc, int time, int type, int flags, int value, const char *name);
 extern void remove_event(struct event *event);
 extern void update_event_name(struct dive *d, struct event* event, char *name);
 extern void per_cylinder_mean_depth(struct dive *dive, struct divecomputer *dc, int *mean, int *duration);
diff --git a/load-git.c b/load-git.c
index e61a0ca13..16aa1958f 100644
--- a/load-git.c
+++ b/load-git.c
@@ -529,6 +529,13 @@ static void parse_event_keyvalue(void *_event, const char *key, const char *valu
 		event->value = val;
 	} else if (!strcmp(key, "name")) {
 		/* We get the name from the string handling */
+	} else if (!strcmp(key, "cylinder")) {
+		/* NOTE! We add one here as a marker that "yes, we got a cylinder index" */
+		event->gas.index = 1+get_index(value);
+	} else if (!strcmp(key, "o2")) {
+		event->gas.mix.o2 = get_fraction(value);
+	} else if (!strcmp(key, "he")) {
+		event->gas.mix.he = get_fraction(value);
 	} else
 		report_error("Unexpected event key/value pair (%s/%s)", key, value);
 }
@@ -538,7 +545,7 @@ static void parse_dc_event(char *line, struct membuffer *str, void *_dc)
 	int m, s = 0;
 	const char *name;
 	struct divecomputer *dc = _dc;
-	struct event event = { 0 };
+	struct event event = { 0 }, *ev;
 
 	m = strtol(line, &line, 10);
 	if (*line == ':')
@@ -557,7 +564,17 @@ static void parse_dc_event(char *line, struct membuffer *str, void *_dc)
 	name = "";
 	if (str->len)
 		name = mb_cstring(str);
-	add_event(dc, event.time.seconds, event.type, event.flags, event.value, name);
+	ev = add_event(dc, event.time.seconds, event.type, event.flags, event.value, name);
+	if (ev && event_is_gaschange(ev)) {
+		/*
+		 * We subtract one here because "0" is "no index",
+		 * and the parsing will add one for actual cylinder
+		 * index data (see parse_event_keyvalue)
+		 */
+		ev->gas.index = event.gas.index-1;
+		if (event.gas.mix.o2.permille || event.gas.mix.he.permille)
+			ev->gas.mix = event.gas.mix;
+	}
 }
 
 static void parse_trip_date(char *line, struct membuffer *str, void *_trip)
diff --git a/parse-xml.c b/parse-xml.c
index 6e74e8aaf..e88c9b944 100644
--- a/parse-xml.c
+++ b/parse-xml.c
@@ -95,17 +95,17 @@ const struct units IMPERIAL_units = IMPERIAL_UNITS;
 /*
  * Dive info as it is being built up..
  */
+#define MAX_EVENT_NAME 128
 static struct divecomputer *cur_dc;
 static struct dive *cur_dive;
 static dive_trip_t *cur_trip = NULL;
 static struct sample *cur_sample;
 static struct picture *cur_picture;
-static struct {
-	int active;
-	duration_t time;
-	int type, flags, value;
-	const char *name;
-} cur_event;
+static union {
+	struct event event;
+	char allocation[sizeof(struct event)+MAX_EVENT_NAME];
+} event_allocation = { .event.deleted = 1 };
+#define cur_event event_allocation.event
 static struct {
 	struct {
 		const char *model;
@@ -527,6 +527,15 @@ static void utf8_string(char *buffer, void *_res)
 		*res = strdup(buffer);
 }
 
+static void event_name(char *buffer, char *name)
+{
+	int size = trimspace(buffer);
+	if (size >= MAX_EVENT_NAME)
+		size = MAX_EVENT_NAME-1;
+	memcpy(name, buffer, size);
+	name[size] = 0;
+}
+
 /* Extract the dive computer type from the xml text buffer */
 static void get_dc_type(char *buffer, enum dive_comp_type *i)
 {
@@ -704,16 +713,22 @@ static void try_to_match_autogroup(const char *name, char *buf)
 
 void add_gas_switch_event(struct dive *dive, struct divecomputer *dc, int seconds, int idx)
 {
-	/* The gas switch event format is insane. It will be fixed, I think */
-	int o2 = get_o2(&dive->cylinder[idx].gasmix);
-	int he = get_he(&dive->cylinder[idx].gasmix);
+	/* The gas switch event format is insane for historical reasons */
+	struct gasmix *mix = &dive->cylinder[idx].gasmix;
+	int o2 = get_o2(mix);
+	int he = get_he(mix);
+	struct event *ev;
 	int value;
 
 	o2 = (o2 + 5) / 10;
 	he = (he + 5) / 10;
 	value = o2 + (he << 16);
 
-	add_event(dc, seconds, he ? SAMPLE_EVENT_GASCHANGE2 : SAMPLE_EVENT_GASCHANGE, 0, value, "gaschange");
+	ev = add_event(dc, seconds, he ? SAMPLE_EVENT_GASCHANGE2 : SAMPLE_EVENT_GASCHANGE, 0, value, "gaschange");
+	if (ev) {
+		ev->gas.index = idx;
+		ev->gas.mix = *mix;
+	}
 }
 
 static void get_cylinderindex(char *buffer, uint8_t *i)
@@ -751,9 +766,9 @@ static void try_to_fill_dc_settings(const char *name, char *buf)
 static void try_to_fill_event(const char *name, char *buf)
 {
 	start_match("event", name, buf);
-	if (MATCH("event", utf8_string, &cur_event.name))
+	if (MATCH("event", event_name, cur_event.name))
 		return;
-	if (MATCH("name", utf8_string, &cur_event.name))
+	if (MATCH("name", event_name, cur_event.name))
 		return;
 	if (MATCH("time", eventtime, &cur_event.time))
 		return;
@@ -763,6 +778,15 @@ static void try_to_fill_event(const char *name, char *buf)
 		return;
 	if (MATCH("value", get_index, &cur_event.value))
 		return;
+	if (MATCH("cylinder", get_index, &cur_event.gas.index)) {
+		/* We add one to indicate that we got an actual cylinder index value */
+		cur_event.gas.index++;
+		return;
+	}
+	if (MATCH("o2", percent, &cur_event.gas.mix.o2))
+		return;
+	if (MATCH("he", percent, &cur_event.gas.mix.he))
+		return;
 	nonmatch("event", name, buf);
 }
 
@@ -1332,36 +1356,38 @@ static void trip_end(void)
 static void event_start(void)
 {
 	memset(&cur_event, 0, sizeof(cur_event));
-	cur_event.active = 1;
+	cur_event.deleted = 0;	/* Active */
 }
 
 static void event_end(void)
 {
 	struct divecomputer *dc = get_dc();
-	if (cur_event.name) {
-		if (strcmp(cur_event.name, "surface") != 0) {
-			/* 123 is a magic event that we used for a while to encode images in dives */
-			if (cur_event.type == 123) {
-				struct picture *pic = alloc_picture();
-				pic->filename = strdup(cur_event.name);
-				/* theoretically this could fail - but we didn't support multi year offsets */
-				pic->offset.seconds = cur_event.time.seconds;
-				dive_add_picture(cur_dive, pic);
-			} else {
-				/* At some point gas change events did not have any type. Thus we need to add
-				 * one on import, if we encounter the type one missing.
-				 */
-				if (cur_event.type == 0 && strcmp(cur_event.name, "gaschange") == 0)
-					cur_event.type = cur_event.value >> 16 > 0 ? SAMPLE_EVENT_GASCHANGE2 : SAMPLE_EVENT_GASCHANGE;
-
-				add_event(dc, cur_event.time.seconds,
-					  cur_event.type, cur_event.flags,
-					  cur_event.value, cur_event.name);
+	if (strcmp(cur_event.name, "surface") != 0) {			/* 123 is a magic event that we used for a while to encode images in dives */
+		if (cur_event.type == 123) {
+			struct picture *pic = alloc_picture();
+			pic->filename = strdup(cur_event.name);
+			/* theoretically this could fail - but we didn't support multi year offsets */
+			pic->offset.seconds = cur_event.time.seconds;
+			dive_add_picture(cur_dive, pic);
+		} else {
+			struct event *ev;
+			/* At some point gas change events did not have any type. Thus we need to add
+			 * one on import, if we encounter the type one missing.
+			 */
+			if (cur_event.type == 0 && strcmp(cur_event.name, "gaschange") == 0)
+				cur_event.type = cur_event.value >> 16 > 0 ? SAMPLE_EVENT_GASCHANGE2 : SAMPLE_EVENT_GASCHANGE;
+			ev = add_event(dc, cur_event.time.seconds,
+				       cur_event.type, cur_event.flags,
+				       cur_event.value, cur_event.name);
+			if (ev && event_is_gaschange(ev)) {
+				/* See try_to_fill_event() on why the filled-in index is one too big */
+				ev->gas.index = cur_event.gas.index-1;
+				if (cur_event.gas.mix.o2.permille || cur_event.gas.mix.he.permille)
+					ev->gas.mix = cur_event.gas.mix;
 			}
 		}
-		free((void *)cur_event.name);
 	}
-	cur_event.active = 0;
+	cur_event.deleted = 1;	/* No longer active */
 }
 
 static void picture_start(void)
@@ -1472,7 +1498,7 @@ static void entry(const char *name, char *buf)
 		try_to_match_autogroup(name, buf);
 		return;
 	}
-	if (cur_event.active) {
+	if (!cur_event.deleted) {
 		try_to_fill_event(name, buf);
 		return;
 	}
@@ -1722,71 +1748,71 @@ extern int dm4_events(void *handle, int columns, char **data, char **column)
 		switch (atoi(data[2])) {
 		case 1:
 			/* 1 Mandatory Safety Stop */
-			cur_event.name = strdup("safety stop (mandatory)");
+			strcpy(cur_event.name, "safety stop (mandatory)");
 			break;
 		case 3:
 			/* 3 Deco */
 			/* What is Subsurface's term for going to
 				 * deco? */
-			cur_event.name = strdup("deco");
+			strcpy(cur_event.name, "deco");
 			break;
 		case 4:
 			/* 4 Ascent warning */
-			cur_event.name = strdup("ascent");
+			strcpy(cur_event.name, "ascent");
 			break;
 		case 5:
 			/* 5 Ceiling broken */
-			cur_event.name = strdup("violation");
+			strcpy(cur_event.name, "violation");
 			break;
 		case 6:
 			/* 6 Mandatory safety stop ceiling error */
-			cur_event.name = strdup("violation");
+			strcpy(cur_event.name, "violation");
 			break;
 		case 7:
 			/* 7 Below deco floor */
-			cur_event.name = strdup("below floor");
+			strcpy(cur_event.name, "below floor");
 			break;
 		case 8:
 			/* 8 Dive time alarm */
-			cur_event.name = strdup("divetime");
+			strcpy(cur_event.name, "divetime");
 			break;
 		case 9:
 			/* 9 Depth alarm */
-			cur_event.name = strdup("maxdepth");
+			strcpy(cur_event.name, "maxdepth");
 			break;
 		case 10:
 		/* 10 OLF 80% */
 		case 11:
 			/* 11 OLF 100% */
-			cur_event.name = strdup("OLF");
+			strcpy(cur_event.name, "OLF");
 			break;
 		case 12:
 			/* 12 High pO₂ */
-			cur_event.name = strdup("PO2");
+			strcpy(cur_event.name, "PO2");
 			break;
 		case 13:
 			/* 13 Air time */
-			cur_event.name = strdup("airtime");
+			strcpy(cur_event.name, "airtime");
 			break;
 		case 17:
 			/* 17 Ascent warning */
-			cur_event.name = strdup("ascent");
+			strcpy(cur_event.name, "ascent");
 			break;
 		case 18:
 			/* 18 Ceiling error */
-			cur_event.name = strdup("ceiling");
+			strcpy(cur_event.name, "ceiling");
 			break;
 		case 19:
 			/* 19 Surfaced */
-			cur_event.name = strdup("surface");
+			strcpy(cur_event.name, "surface");
 			break;
 		case 20:
 			/* 20 Deco */
-			cur_event.name = strdup("deco");
+			strcpy(cur_event.name, "deco");
 			break;
 		case 22:
 			/* 22 Mandatory safety stop violation */
-			cur_event.name = strdup("violation");
+			strcpy(cur_event.name, "violation");
 			break;
 		case 257:
 			/* 257 Dive active */
@@ -1796,14 +1822,14 @@ extern int dm4_events(void *handle, int columns, char **data, char **column)
 		case 258:
 			/* 258 Bookmark */
 			if (data[3]) {
-				cur_event.name = strdup("heading");
+				strcpy(cur_event.name, "heading");
 				cur_event.value = atoi(data[3]);
 			} else {
-				cur_event.name = strdup("bookmark");
+				strcpy(cur_event.name, "bookmark");
 			}
 			break;
 		default:
-			cur_event.name = strdup("unknown");
+			strcpy(cur_event.name, "unknown");
 			cur_event.value = atoi(data[2]);
 			break;
 		}
@@ -1986,7 +2012,7 @@ extern int shearwater_changes(void *handle, int columns, char **data, char **col
 	if (data[0])
 		cur_event.time.seconds = atoi(data[0]);
 	if (data[1]) {
-		cur_event.name = strdup("gaschange");
+		strcpy(cur_event.name, "gaschange");
 		cur_event.value = atof(data[1]) * 100;
 	}
 	event_end();
diff --git a/profile.c b/profile.c
index 71a9164e6..79917d6e6 100644
--- a/profile.c
+++ b/profile.c
@@ -289,6 +289,14 @@ struct plot_info *analyze_plot_info(struct plot_info *pi)
 	return pi;
 }
 
+/*
+ * If the event has an explicit cylinder index,
+ * we return that. If it doesn't, we return the best
+ * match based on the gasmix.
+ *
+ * Some dive computers give cylinder indexes, some
+ * give just the gas mix.
+ */
 int get_cylinder_index(struct dive *dive, struct event *ev)
 {
 	int i;
@@ -296,10 +304,9 @@ int get_cylinder_index(struct dive *dive, struct event *ev)
 	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.
-	 */
+	if (ev->gas.index >= 0)
+		return ev->gas.index;
+
 	g = get_gasmix_from_event(ev);
 	target_o2 = get_o2(g);
 	target_he = get_he(g);
@@ -318,13 +325,8 @@ int get_cylinder_index(struct dive *dive, struct event *ev)
 		delta_o2 = get_o2(&cyl->gasmix) - target_o2;
 		delta_he = get_he(&cyl->gasmix) - target_he;
 		distance = delta_o2 * delta_o2;
+		distance += delta_he * delta_he;
 
-		/* Check the event type to figure out if we should care about the he part.
-		 * SAMPLE_EVENT_GASCHANGE, aka without he
-		 * SAMPLE_EVENT_GASCHANGE2, aka with he
-		 */
-		if (ev->type == SAMPLE_EVENT_GASCHANGE2)
-			distance += delta_he * delta_he;
 		if (distance >= score)
 			continue;
 		score = distance;
diff --git a/qt-ui/profile/diveeventitem.cpp b/qt-ui/profile/diveeventitem.cpp
index b9bb4482b..c1ea48544 100644
--- a/qt-ui/profile/diveeventitem.cpp
+++ b/qt-ui/profile/diveeventitem.cpp
@@ -66,10 +66,10 @@ void DiveEventItem::setupPixmap()
 		setPixmap(EVENT_PIXMAP(":flag"));
 	} else if (strcmp(internalEvent->name, "heading") == 0) {
 		setPixmap(EVENT_PIXMAP(":flag"));
-	} else if (internalEvent->type == SAMPLE_EVENT_GASCHANGE || internalEvent->type == SAMPLE_EVENT_GASCHANGE2) {
-		if (internalEvent->value >> 16)
+	} else if (event_is_gaschange(internalEvent)) {
+		if (internalEvent->gas.mix.he.permille)
 			setPixmap(EVENT_PIXMAP_BIGGER(":gaschangeTrimix"));
-		else if (internalEvent->value == 0)
+		else if (gasmix_is_air(&internalEvent->gas.mix))
 			setPixmap(EVENT_PIXMAP_BIGGER(":gaschangeAir"));
 		else
 			setPixmap(EVENT_PIXMAP_BIGGER(":gaschangeNitrox"));
@@ -86,7 +86,7 @@ void DiveEventItem::setupToolTipString()
 	int value = internalEvent->value;
 	int type = internalEvent->type;
 	if (value) {
-		if (type == SAMPLE_EVENT_GASCHANGE || type == SAMPLE_EVENT_GASCHANGE2) {
+		if (event_is_gaschange(internalEvent)) {
 			QModelIndexList result = dataModel->match(dataModel->index(0, DivePlotDataModel::TIME), Qt::DisplayRole, internalEvent->time.seconds);
 			if (result.isEmpty()) {
 				Q_ASSERT("can't find a spot in the dataModel");
diff --git a/save-git.c b/save-git.c
index a1ef022fb..308a02c83 100644
--- a/save-git.c
+++ b/save-git.c
@@ -119,6 +119,18 @@ static void save_tags(struct membuffer *b, struct tag_entry *tags)
 	put_string(b, "\n");
 }
 
+static void put_gasmix(struct membuffer *b, struct gasmix *mix)
+{
+	int o2 = mix->o2.permille;
+	int he = mix->he.permille;
+
+	if (o2) {
+		put_format(b, " o2=%u.%u%%", FRACTION(o2, 10));
+		if (he)
+			put_format(b, " he=%u.%u%%", FRACTION(he, 10));
+	}
+}
+
 static void save_cylinder_info(struct membuffer *b, struct dive *dive)
 {
 	int i, nr;
@@ -128,8 +140,6 @@ static void save_cylinder_info(struct membuffer *b, struct dive *dive)
 		cylinder_t *cylinder = dive->cylinder + i;
 		int volume = cylinder->type.size.mliter;
 		const char *description = cylinder->type.description;
-		int o2 = cylinder->gasmix.o2.permille;
-		int he = cylinder->gasmix.he.permille;
 
 		put_string(b, "cylinder");
 		if (volume)
@@ -137,11 +147,7 @@ static void save_cylinder_info(struct membuffer *b, struct dive *dive)
 		put_pressure(b, cylinder->type.workingpressure, " workpressure=", "bar");
 		show_utf8(b, " description=", description, "");
 		strip_mb(b);
-		if (o2) {
-			put_format(b, " o2=%u.%u%%", FRACTION(o2, 10));
-			if (he)
-				put_format(b, " he=%u.%u%%", FRACTION(he, 10));
-		}
+		put_gasmix(b, &cylinder->gasmix);
 		put_pressure(b, cylinder->start, " start=", "bar");
 		put_pressure(b, cylinder->end, " end=", "bar");
 		put_string(b, "\n");
@@ -292,6 +298,13 @@ static void save_one_event(struct membuffer *b, struct event *ev)
 	show_index(b, ev->flags, "flags=", "");
 	show_index(b, ev->value, "value=", "");
 	show_utf8(b, " name=", ev->name, "");
+	if (event_is_gaschange(ev)) {
+		if (ev->gas.index >= 0) {
+			show_index(b, ev->gas.index, "cylinder=", "");
+			put_gasmix(b, &ev->gas.mix);
+		} else if (!event_gasmix_redundant(ev))
+			put_gasmix(b, &ev->gas.mix);
+	}
 	put_string(b, "\n");
 }
 
diff --git a/save-xml.c b/save-xml.c
index fe804cb6d..e9f769d3f 100644
--- a/save-xml.c
+++ b/save-xml.c
@@ -148,6 +148,18 @@ static void save_overview(struct membuffer *b, struct dive *dive)
 	show_utf8(b, dive->suit, "  <suit>", "</suit>\n", 0);
 }
 
+static void put_gasmix(struct membuffer *b, struct gasmix *mix)
+{
+	int o2 = mix->o2.permille;
+	int he = mix->he.permille;
+
+	if (o2) {
+		put_format(b, " o2='%u.%u%%'", FRACTION(o2, 10));
+		if (he)
+			put_format(b, " he='%u.%u%%'", FRACTION(he, 10));
+	}
+}
+
 static void save_cylinder_info(struct membuffer *b, struct dive *dive)
 {
 	int i, nr;
@@ -158,19 +170,13 @@ static void save_cylinder_info(struct membuffer *b, struct dive *dive)
 		cylinder_t *cylinder = dive->cylinder + i;
 		int volume = cylinder->type.size.mliter;
 		const char *description = cylinder->type.description;
-		int o2 = cylinder->gasmix.o2.permille;
-		int he = cylinder->gasmix.he.permille;
 
 		put_format(b, "  <cylinder");
 		if (volume)
 			put_milli(b, " size='", volume, " l'");
 		put_pressure(b, cylinder->type.workingpressure, " workpressure='", " bar'");
 		show_utf8(b, description, " description='", "'", 1);
-		if (o2) {
-			put_format(b, " o2='%u.%u%%'", FRACTION(o2, 10));
-			if (he)
-				put_format(b, " he='%u.%u%%'", FRACTION(he, 10));
-		}
+		put_gasmix(b, &cylinder->gasmix);
 		put_pressure(b, cylinder->start, " start='", " bar'");
 		put_pressure(b, cylinder->end, " end='", " bar'");
 		put_format(b, " />\n");
@@ -261,6 +267,13 @@ static void save_one_event(struct membuffer *b, struct event *ev)
 	show_index(b, ev->flags, "flags='", "'");
 	show_index(b, ev->value, "value='", "'");
 	show_utf8(b, ev->name, " name='", "'", 1);
+	if (event_is_gaschange(ev)) {
+		if (ev->gas.index >= 0) {
+			show_index(b, ev->gas.index, "cylinder='", "'");
+			put_gasmix(b, &ev->gas.mix);
+		} else if (!event_gasmix_redundant(ev))
+			put_gasmix(b, &ev->gas.mix);
+	}
 	put_format(b, " />\n");
 }