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>

1 files changed, 3 insertions, 3 deletions

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)