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>

4 files changed, 16 insertions, 16 deletions

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)