Cleanup: return gasmix by value

Currently, get_gasmix_from_event() and get_gasmix() return pointers
to either static or to (possibly changing) dive data. This seems like
a dangerous practice and the returned data should be used immediately.

Instead, return the gasmix by value. This is in preparation of
const-ifying input parameters of a number of core functions, which
will ultimately let the merge() function take const-arguments in
preparation of undo of dive-merging.

On common 64-bit systems gasmix (two "int"s) is the size of a pointer
and can be returned in a register.

On 32-bit systems a pointer to the struct to be filled out will be
passed.

Since get_gasmix() now returns a value, the first invocation is
tested by a NULL-initialized "struct event *". Document this in
a comment.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

10 files changed, 65 insertions, 55 deletions

diff --git a/core/dive.c b/core/dive.c
index da4b19346..6d9945932 100644
--- a/core/dive.c
+++ b/core/dive.c
@@ -270,17 +270,16 @@ enum divemode_t get_current_divemode(struct divecomputer *dc, int time, struct e
 	return *divemode;
 }
 
-/* this returns a pointer to static variable - so use it right away after calling */
-struct gasmix *get_gasmix_from_event(struct dive *dive, struct event *ev)
+struct gasmix get_gasmix_from_event(struct dive *dive, struct event *ev)
 {
-	static struct gasmix dummy;
+	struct gasmix dummy = { 0 };
 	if (ev && event_is_gaschange(ev)) {
 		int index = ev->gas.index;
 		if (index >= 0 && index < MAX_CYLINDERS)
-			return &dive->cylinder[index].gasmix;
-		return &ev->gas.mix;
+			return dive->cylinder[index].gasmix;
+		return ev->gas.mix;
 	}
-	return &dummy;
+	return dummy;
 }
 
 int get_pressure_units(int mb, const char **units)
@@ -1073,7 +1072,7 @@ void update_setpoint_events(struct dive *dive, struct divecomputer *dc)
 		// So we make sure, this comes from a Predator or Petrel and we only remove
 		// pO2 values we would have computed anyway.
 		struct event *ev = get_next_event(dc->events, "gaschange");
-		struct gasmix *gasmix = get_gasmix_from_event(dive, ev);
+		struct gasmix gasmix = get_gasmix_from_event(dive, ev);
 		struct event *next = get_next_event(ev, "gaschange");
 
 		for (int i = 0; i < dc->samples; i++) {
@@ -1083,7 +1082,7 @@ void update_setpoint_events(struct dive *dive, struct divecomputer *dc)
 				gasmix = get_gasmix_from_event(dive, ev);
 				next = get_next_event(ev, "gaschange");
 			}
-			fill_pressures(&pressures, calculate_depth_to_mbar(dc->sample[i].depth.mm, dc->surface_pressure, 0), gasmix ,0, dc->divemode);
+			fill_pressures(&pressures, calculate_depth_to_mbar(dc->sample[i].depth.mm, dc->surface_pressure, 0), &gasmix ,0, dc->divemode);
 			if (abs(dc->sample[i].setpoint.mbar - (int)(1000 * pressures.o2)) <= 50)
 				dc->sample[i].setpoint.mbar = 0;
 		}
@@ -4288,19 +4287,24 @@ int dive_has_gps_location(struct dive *dive)
 	return dive_site_has_gps_location(get_dive_site_by_uuid(dive->dive_site_uuid));
 }
 
-struct gasmix *get_gasmix(struct dive *dive, struct divecomputer *dc, int time, struct event **evp, struct gasmix *gasmix)
+struct gasmix get_gasmix(struct dive *dive, struct divecomputer *dc, int time, struct event **evp, struct gasmix *gasmix)
 {
 	struct event *ev = *evp;
+	struct gasmix res;
 
-	if (!gasmix) {
+	if (!ev) {
+		/* on first invocation, get initial gas mix and first event (if any) */
 		int cyl = explicit_first_cylinder(dive, dc);
-		gasmix = &dive->cylinder[cyl].gasmix;
+		res = dive->cylinder[cyl].gasmix;
 		ev = dc ? get_next_event(dc->events, "gaschange") : NULL;
+	} else {
+		res = *gasmix;
 	}
+
 	while (ev && ev->time.seconds < time) {
-		gasmix = get_gasmix_from_event(dive, ev);
+		res = get_gasmix_from_event(dive, ev);
 		ev = get_next_event(ev->next, "gaschange");
 	}
 	*evp = ev;
-	return gasmix;
+	return res;
 }
diff --git a/core/dive.h b/core/dive.h
index 98ac06fdc..7e62262d9 100644
--- a/core/dive.h
+++ b/core/dive.h
@@ -585,7 +585,7 @@ extern void update_event_name(struct dive *d, struct event* event, const char *n
 extern void add_extra_data(struct divecomputer *dc, const char *key, const char *value);
 extern void per_cylinder_mean_depth(struct dive *dive, struct divecomputer *dc, int *mean, int *duration);
 extern int get_cylinder_index(struct dive *dive, struct event *ev);
-extern struct gasmix *get_gasmix_from_event(struct dive *, struct event *ev);
+extern struct gasmix get_gasmix_from_event(struct dive *, struct event *ev);
 extern int nr_cylinders(struct dive *dive);
 extern int nr_weightsystems(struct dive *dive);
 
@@ -718,7 +718,11 @@ extern void printdecotable(struct decostop *table);
 
 extern struct event *get_next_event(struct event *event, const char *name);
 
-extern struct gasmix *get_gasmix(struct dive *dive, struct divecomputer *dc, int time, struct event **evp, struct gasmix *gasmix);
+/* Get gasmix at increasing timestamps.
+ * In "evp", pass a pointer to a "struct event *" which is NULL-initialized on first invocation.
+ * On subsequent calls, pass the same "evp" and the "gasmix" from previous calls.
+ */
+extern struct gasmix get_gasmix(struct dive *dive, struct divecomputer *dc, int time, struct event **evp, struct gasmix *gasmix);
 
 /* these structs holds the information that
  * describes the cylinders / weight systems.
diff --git a/core/divelist.c b/core/divelist.c
index b81e89d25..9c2484417 100644
--- a/core/divelist.c
+++ b/core/divelist.c
@@ -404,7 +404,7 @@ static int calculate_sac(struct dive *dive)
 static void add_dive_to_deco(struct deco_state *ds, struct dive *dive)
 {
 	struct divecomputer *dc = &dive->dc;
-	struct gasmix *gasmix = NULL;
+	struct gasmix gasmix = { 0 };
 	int i;
 	struct event *ev = NULL, *evd = NULL;
 	enum divemode_t current_divemode = UNDEF_COMP_TYPE;
@@ -421,8 +421,8 @@ static void add_dive_to_deco(struct deco_state *ds, struct dive *dive)
 
 		for (j = t0; j < t1; j++) {
 			int depth = interpolate(psample->depth.mm, sample->depth.mm, j - t0, t1 - t0);
-			gasmix = get_gasmix(dive, dc, j, &ev, gasmix);
-			add_segment(ds, depth_to_bar(depth, dive), gasmix, 1, sample->setpoint.mbar,
+			gasmix = get_gasmix(dive, dc, j, &ev, &gasmix);
+			add_segment(ds, depth_to_bar(depth, dive), &gasmix, 1, sample->setpoint.mbar,
 				get_current_divemode(&dive->dc, j, &evd, &current_divemode), dive->sac);
 		}
 	}
diff --git a/core/profile.c b/core/profile.c
index 113f62845..56cc85aac 100644
--- a/core/profile.c
+++ b/core/profile.c
@@ -319,7 +319,7 @@ struct plot_info *analyze_plot_info(struct plot_info *pi)
 int get_cylinder_index(struct dive *dive, struct event *ev)
 {
 	int best;
-	struct gasmix *mix;
+	struct gasmix mix;
 
 	if (ev->gas.index >= 0)
 		return ev->gas.index;
@@ -333,7 +333,7 @@ int get_cylinder_index(struct dive *dive, struct event *ev)
 	fprintf(stderr, "Still looking up cylinder based on gas mix in get_cylinder_index()!\n");
 
 	mix = get_gasmix_from_event(dive, ev);
-	best = find_best_gasmix_match(mix, dive->cylinder, 0);
+	best = find_best_gasmix_match(&mix, dive->cylinder, 0);
 	return best < 0 ? 0 : best;
 }
 
@@ -775,16 +775,16 @@ static unsigned int matching_gases(struct dive *dive, struct gasmix *gasmix)
 
 static void calculate_sac(struct dive *dive, struct divecomputer *dc, struct plot_info *pi)
 {
-	struct gasmix *gasmix = NULL;
+	struct gasmix gasmix = { 0 };
 	struct event *ev = NULL;
 	unsigned int gases = 0;
 
 	for (int i = 0; i < pi->nr; i++) {
 		struct plot_data *entry = pi->entry + i;
-		struct gasmix *newmix = get_gasmix(dive, dc, entry->sec, &ev, gasmix);
-		if (newmix != gasmix) {
+		struct gasmix newmix = get_gasmix(dive, dc, entry->sec, &ev, &gasmix);
+		if (!same_gasmix(&newmix, &gasmix)) {
 			gasmix = newmix;
-			gases = matching_gases(dive, newmix);
+			gases = matching_gases(dive, &newmix);
 		}
 
 		fill_sac(dive, pi, i, gases);
@@ -1016,7 +1016,7 @@ void calculate_deco_information(struct deco_state *ds, struct deco_state *planne
 		int last_ndl_tts_calc_time = 0, first_ceiling = 0, current_ceiling, last_ceiling = 0, final_tts = 0 , time_clear_ceiling = 0;
 		if (decoMode() == VPMB)
 			ds->first_ceiling_pressure.mbar = depth_to_mbar(first_ceiling, dive);
-		struct gasmix *gasmix = NULL;
+		struct gasmix gasmix = { 0 };
 		struct event *ev = NULL, *evd = NULL;
 		enum divemode_t current_divemode = UNDEF_COMP_TYPE;
 
@@ -1026,7 +1026,7 @@ void calculate_deco_information(struct deco_state *ds, struct deco_state *planne
 			int time_stepsize = 20;
 
 			current_divemode = get_current_divemode(dc, entry->sec, &evd, &current_divemode);
-			gasmix = get_gasmix(dive, dc, t1, &ev, gasmix);
+			gasmix = get_gasmix(dive, dc, t1, &ev, &gasmix);
 			entry->ambpressure = depth_to_bar(entry->depth, dive);
 			entry->gfline = get_gf(ds, entry->ambpressure, dive) * (100.0 - AMB_PERCENTAGE) + AMB_PERCENTAGE;
 			if (t0 > t1) {
@@ -1040,7 +1040,7 @@ void calculate_deco_information(struct deco_state *ds, struct deco_state *planne
 			for (j = t0 + time_stepsize; j <= t1; j += time_stepsize) {
 				int depth = interpolate(entry[-1].depth, entry[0].depth, j - t0, t1 - t0);
 				add_segment(ds, depth_to_bar(depth, dive),
-					    gasmix, time_stepsize, entry->o2pressure.mbar, current_divemode, entry->sac);
+					    &gasmix, time_stepsize, entry->o2pressure.mbar, current_divemode, entry->sac);
 				entry->icd_warning = ds->icd_warning;
 				if ((t1 - j < time_stepsize) && (j < t1))
 					time_stepsize = t1 - j;
@@ -1115,7 +1115,7 @@ void calculate_deco_information(struct deco_state *ds, struct deco_state *planne
 				/* We are going to mess up deco state, so store it for later restore */
 				struct deco_state *cache_data = NULL;
 				cache_deco_state(ds, &cache_data);
-				calculate_ndl_tts(ds, dive, entry, gasmix, surface_pressure, current_divemode);
+				calculate_ndl_tts(ds, dive, entry, &gasmix, surface_pressure, current_divemode);
 				if (decoMode() == VPMB && !in_planner() && i == pi->nr - 1)
 					final_tts = entry->tts_calc;
 				/* Restore "real" deco state for next real time step */
@@ -1205,7 +1205,7 @@ static void calculate_gas_information_new(struct dive *dive, struct divecomputer
 {
 	int i;
 	double amb_pressure;
-	struct gasmix *gasmix = NULL;
+	struct gasmix gasmix = { 0 };
 	struct event *evg = NULL, *evd = NULL;
 	enum divemode_t current_divemode = UNDEF_COMP_TYPE;
 
@@ -1213,21 +1213,23 @@ static void calculate_gas_information_new(struct dive *dive, struct divecomputer
 		int fn2, fhe;
 		struct plot_data *entry = pi->entry + i;
 
-		gasmix = get_gasmix(dive, dc, entry->sec, &evg, gasmix);
+		gasmix = get_gasmix(dive, dc, entry->sec, &evg, &gasmix);
 		amb_pressure = depth_to_bar(entry->depth, dive);
 		current_divemode = get_current_divemode(dc, entry->sec, &evd, &current_divemode);
-		fill_pressures(&entry->pressures, amb_pressure, gasmix, (current_divemode == OC) ? 0.0 : entry->o2pressure.mbar / 1000.0, current_divemode);
+		fill_pressures(&entry->pressures, amb_pressure, &gasmix, (current_divemode == OC) ? 0.0 : entry->o2pressure.mbar / 1000.0, current_divemode);
 		fn2 = (int)(1000.0 * entry->pressures.n2 / amb_pressure);
 		fhe = (int)(1000.0 * entry->pressures.he / amb_pressure);
-		if (dc->divemode == PSCR) // OC pO2 is calulated for PSCR with or without external PO2 monitoring.
-			entry->scr_OC_pO2.mbar = (int) depth_to_mbar(entry->depth, dive) * get_o2(get_gasmix(dive, dc, entry->sec, &evg, gasmix)) / 1000;
+		if (dc->divemode == PSCR) { // OC pO2 is calulated for PSCR with or without external PO2 monitoring.
+			struct gasmix gasmix2 = get_gasmix(dive, dc, entry->sec, &evg, &gasmix);
+			entry->scr_OC_pO2.mbar = (int) depth_to_mbar(entry->depth, dive) * get_o2(&gasmix2) / 1000;
+		}
 
 		/* Calculate MOD, EAD, END and EADD based on partial pressures calculated before
 		 * so there is no difference in calculating between OC and CC
 		 * END takes O₂ + N₂ (air) into account ("Narcotic" for trimix dives)
 		 * EAD just uses N₂ ("Air" for nitrox dives) */
 		pressure_t modpO2 = { .mbar = (int)(prefs.modpO2 * 1000) };
-		entry->mod = (double)gas_mod(gasmix, modpO2, dive, 1).mm;
+		entry->mod = (double)gas_mod(&gasmix, modpO2, dive, 1).mm;
 		entry->end = (entry->depth + 10000) * (1000 - fhe) / 1000.0 - 10000;
 		entry->ead = (entry->depth + 10000) * fn2 / (double)N2_IN_AIR - 10000;
 		entry->eadd = (entry->depth + 10000) *
@@ -1235,7 +1237,7 @@ static void calculate_gas_information_new(struct dive *dive, struct divecomputer
 				       entry->pressures.n2 / amb_pressure * N2_DENSITY +
 				       entry->pressures.he / amb_pressure * HE_DENSITY) /
 				      (O2_IN_AIR * O2_DENSITY + N2_IN_AIR * N2_DENSITY) * 1000 - 10000;
-		entry->density = gas_density(gasmix, depth_to_mbar(entry->depth, dive));
+		entry->density = gas_density(&gasmix, depth_to_mbar(entry->depth, dive));
 		if (entry->mod < 0)
 			entry->mod = 0;
 		if (entry->ead < 0)
diff --git a/core/save-git.c b/core/save-git.c
index fcfbd93d1..7717a4b5f 100644
--- a/core/save-git.c
+++ b/core/save-git.c
@@ -382,10 +382,10 @@ static void save_one_event(struct membuffer *b, struct dive *dive, struct event
 		show_index(b, ev->value, "value=", "");
 	show_utf8(b, " name=", ev->name, "");
 	if (event_is_gaschange(ev)) {
-		struct gasmix *mix = get_gasmix_from_event(dive, ev);
+		struct gasmix mix = get_gasmix_from_event(dive, ev);
 		if (ev->gas.index >= 0)
 			show_integer(b, ev->gas.index, "cylinder=", "");
-		put_gasmix(b, mix);
+		put_gasmix(b, &mix);
 	}
 	put_string(b, "\n");
 }
diff --git a/core/save-xml.c b/core/save-xml.c
index e3af000a4..7e2328e5c 100644
--- a/core/save-xml.c
+++ b/core/save-xml.c
@@ -307,10 +307,10 @@ static void save_one_event(struct membuffer *b, struct dive *dive, struct event
 		show_index(b, ev->value, "value='", "'");
 	show_utf8(b, ev->name, " name='", "'", 1);
 	if (event_is_gaschange(ev)) {
-		struct gasmix *mix = get_gasmix_from_event(dive, ev);
+		struct gasmix mix = get_gasmix_from_event(dive, ev);
 		if (ev->gas.index >= 0)
 			show_integer(b, ev->gas.index, "cylinder='", "'");
-		put_gasmix(b, mix);
+		put_gasmix(b, &mix);
 	}
 	put_format(b, " />\n");
 }
diff --git a/profile-widget/diveeventitem.cpp b/profile-widget/diveeventitem.cpp
index 13ab3770b..875954b37 100644
--- a/profile-widget/diveeventitem.cpp
+++ b/profile-widget/diveeventitem.cpp
@@ -92,20 +92,20 @@ void DiveEventItem::setupPixmap(struct gasmix *lastgasmix)
 	} else if (internalEvent->type == SAMPLE_EVENT_BOOKMARK) {
 		setPixmap(EVENT_PIXMAP(":dive-bookmark-icon"));
 	} else if (event_is_gaschange(internalEvent)) {
-		struct gasmix *mix = get_gasmix_from_event(&displayed_dive, internalEvent);
+		struct gasmix mix = get_gasmix_from_event(&displayed_dive, internalEvent);
 		struct icd_data icd_data;
-		bool icd = isobaric_counterdiffusion(lastgasmix, mix, &icd_data);
-		if (mix->he.permille) {
+		bool icd = isobaric_counterdiffusion(lastgasmix, &mix, &icd_data);
+		if (mix.he.permille) {
 			if (icd)
 				setPixmap(EVENT_PIXMAP_BIGGER(":gaschange-trimix-ICD-icon"));
 			else
 				setPixmap(EVENT_PIXMAP_BIGGER(":gaschange-trimix-icon"));
-		} else if (gasmix_is_air(mix)) {
+		} else if (gasmix_is_air(&mix)) {
 			if (icd)
 				setPixmap(EVENT_PIXMAP_BIGGER(":gaschange-air-ICD-icon"));
 			else
 				setPixmap(EVENT_PIXMAP_BIGGER(":gaschange-air-icon"));
-		} else if (mix->o2.permille == 1000) {
+		} else if (mix.o2.permille == 1000) {
 			if (icd)
 				setPixmap(EVENT_PIXMAP_BIGGER(":gaschange-oxygen-ICD-icon"));
 			else
@@ -174,15 +174,15 @@ void DiveEventItem::setupToolTipString(struct gasmix *lastgasmix)
 
 	if (event_is_gaschange(internalEvent)) {
 		struct icd_data icd_data;
-		struct gasmix *mix = get_gasmix_from_event(&displayed_dive, internalEvent);
+		struct gasmix mix = get_gasmix_from_event(&displayed_dive, internalEvent);
 		struct membuffer mb = {};
 		name += ": ";
-		name += gasname(mix);
+		name += gasname(&mix);
 
 		/* Do we have an explicit cylinder index?  Show it. */
 		if (internalEvent->gas.index >= 0)
 			name += tr(" (cyl. %1)").arg(internalEvent->gas.index + 1);
-		bool icd = isobaric_counterdiffusion(lastgasmix, mix, &icd_data);
+		bool icd = isobaric_counterdiffusion(lastgasmix, &mix, &icd_data);
 		if (icd_data.dHe < 0) {
 			put_format(&mb, "\n%s %s:%+.3g%% %s:%+.3g%%%s%+.3g%%",
 				qPrintable(tr("ICD")),
@@ -192,7 +192,7 @@ void DiveEventItem::setupToolTipString(struct gasmix *lastgasmix)
 			name += QString::fromUtf8(mb.buffer, mb.len);
 			free_buffer(&mb);
 		}
-		*lastgasmix = *mix;
+		*lastgasmix = mix;
 	} else if (same_string(internalEvent->name, "modechange")) {
 		name += QString(": %1").arg(gettextFromC::tr(divemode_text_ui[internalEvent->value]));
 	} else if (value) {
diff --git a/profile-widget/diveprofileitem.cpp b/profile-widget/diveprofileitem.cpp
index bedefb97e..94fb787b1 100644
--- a/profile-widget/diveprofileitem.cpp
+++ b/profile-widget/diveprofileitem.cpp
@@ -410,11 +410,11 @@ void DivePercentageItem::paint(QPainter *painter, const QStyleOptionGraphicsItem
 	for (int i = 1, modelDataCount = dataModel->rowCount(); i < modelDataCount; i++) {
 		if (i < poly.count()) {
 			double value = dataModel->index(i, vDataColumn).data().toDouble();
-			struct gasmix *gasmix = NULL;
+			struct gasmix gasmix = { 0 };
 			struct event *ev = NULL;
 			int sec = dataModel->index(i, DivePlotDataModel::TIME).data().toInt();
-			gasmix = get_gasmix(&displayed_dive, displayed_dc, sec, &ev, gasmix);
-			int inert = 1000 - get_o2(gasmix);
+			gasmix = get_gasmix(&displayed_dive, displayed_dc, sec, &ev, &gasmix);
+			int inert = 1000 - get_o2(&gasmix);
 			mypen.setBrush(QBrush(ColorScale(value, inert)));
 			painter->setPen(mypen);
 			painter->drawLine(poly[i - 1], poly[i]);
diff --git a/profile-widget/profilewidget2.cpp b/profile-widget/profilewidget2.cpp
index cbd63cf40..d9875681a 100644
--- a/profile-widget/profilewidget2.cpp
+++ b/profile-widget/profilewidget2.cpp
@@ -759,7 +759,7 @@ void ProfileWidget2::plotDive(struct dive *d, bool force, bool doClearPictures)
 	eventItems.clear();
 	struct event *event = currentdc->events;
 	struct event *ev;
-	struct gasmix lastgasmix = *get_gasmix(&displayed_dive, current_dc, 1, &ev, NULL);
+	struct gasmix lastgasmix = get_gasmix(&displayed_dive, current_dc, 1, &ev, NULL);
 
 	while (event) {
 #ifndef SUBSURFACE_MOBILE
diff --git a/profile-widget/tankitem.cpp b/profile-widget/tankitem.cpp
index 22e5d3d21..d1adae41c 100644
--- a/profile-widget/tankitem.cpp
+++ b/profile-widget/tankitem.cpp
@@ -104,7 +104,7 @@ void TankItem::modelDataChanged(const QModelIndex&, const QModelIndex&)
 
 	// start with the first gasmix and at the start of the dive
 	int cyl = explicit_first_cylinder(&displayed_dive, dc);
-	struct gasmix *gasmix = &displayed_dive.cylinder[cyl].gasmix;
+	struct gasmix gasmix = displayed_dive.cylinder[cyl].gasmix;
 	int startTime = 0;
 
 	// work through all the gas changes and add the rectangle for each gas while it was used
@@ -112,14 +112,14 @@ void TankItem::modelDataChanged(const QModelIndex&, const QModelIndex&)
 	while (ev && (int)ev->time.seconds < last_entry->sec) {
 		width = hAxis->posAtValue(ev->time.seconds) - hAxis->posAtValue(startTime);
 		left = hAxis->posAtValue(startTime);
-		createBar(left, width, gasmix);
+		createBar(left, width, &gasmix);
 		startTime = ev->time.seconds;
 		gasmix = get_gasmix_from_event(&displayed_dive, ev);
 		ev = get_next_event(ev->next, "gaschange");
 	}
 	width = hAxis->posAtValue(last_entry->sec) - hAxis->posAtValue(startTime);
 	left = hAxis->posAtValue(startTime);
-	createBar(left, width, gasmix);
+	createBar(left, width, &gasmix);
 }
 
 void TankItem::setHorizontalAxis(DiveCartesianAxis *horizontal)