core: move gas_volume() to cylinder_t

Feels natural in a C++ code base.

The commit is somewhat complex, because it also changes the
return type to volume_t. The units system really needs some
work. :(

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

core/divelist.cpp

@@ -384,7 +384,8 @@ static double calculate_airuse(const struct dive &dive)
 				continue;
 		}
 
-		airuse += gas_volume(&cyl, start) - gas_volume(&cyl, end);
+		// TODO: implement subtraction for units.h types
+		airuse += cyl.gas_volume(start).mliter - cyl.gas_volume(end).mliter;
 	}
 	return airuse / 1000.0;
 }

core/equipment.cpp

@@ -198,11 +198,11 @@ const char *gasname(struct gasmix gasmix)
 	return gas;
 }
 
-int gas_volume(const cylinder_t *cyl, pressure_t p)
+volume_t cylinder_t::gas_volume(pressure_t p) const
 {
 	double bar = p.mbar / 1000.0;
-	double z_factor = gas_compressibility_factor(cyl->gasmix, bar);
-	return lrint(cyl->type.size.mliter * bar_to_atm(bar) / z_factor);
+	double z_factor = gas_compressibility_factor(gasmix, bar);
+	return volume_t { static_cast<int>(lrint(type.size.mliter * bar_to_atm(bar) / z_factor)) };
 }
 
 int find_best_gasmix_match(struct gasmix mix, const struct cylinder_table &cylinders)

core/equipment.h

@@ -35,6 +35,8 @@ struct cylinder_t
 
 	cylinder_t();
 	~cylinder_t();
+
+	volume_t gas_volume(pressure_t p) const; /* Volume of a cylinder at pressure 'p' */
 };
 
 /* Table of cylinders.
@@ -78,7 +80,6 @@ extern enum cylinderuse cylinderuse_from_text(const char *text);
 extern void copy_cylinder_types(const struct dive *s, struct dive *d);
 extern void remove_cylinder(struct dive *dive, int idx);
 extern void reset_cylinders(struct dive *dive, bool track_gas);
-extern int gas_volume(const cylinder_t *cyl, pressure_t p); /* Volume in mliter of a cylinder at pressure 'p' */
 extern int find_best_gasmix_match(struct gasmix mix, const struct cylinder_table &cylinders);
 extern void fill_default_cylinder(const struct dive *dive, cylinder_t *cyl); /* dive is needed to fill out MOD, which depends on salinity. */
 extern cylinder_t default_cylinder(const struct dive *d);

core/libdivecomputer.cpp

@@ -246,8 +246,8 @@ static dc_status_t parse_gasmixes(device_data_t *devdata, struct dive *dive, dc_
 						cyl.type.workingpressure.mbar = lrint(
 							cyl.type.workingpressure.mbar * 206.843 / 206.7 );
 						char name_buffer[17];
-						int rounded_size = lrint(ml_to_cuft(gas_volume(&cyl,
-							cyl.type.workingpressure)));
+						int rounded_size = lrint(ml_to_cuft(cyl.gas_volume(
+							cyl.type.workingpressure).mliter));
 						rounded_size = (int)((rounded_size + 5) / 10) * 10;
 						switch (cyl.type.workingpressure.mbar) {
 						case 206843:

core/profile.cpp

@@ -128,7 +128,8 @@ static int get_local_sac(struct plot_info &pi, int idx1, int idx2, struct dive *
 
 	cyl = dive->get_cylinder(index);
 
-	airuse = gas_volume(cyl, a) - gas_volume(cyl, b);
+	// TODO: Implement addition/subtraction on units.h types
+	airuse = cyl->gas_volume(a).mliter - cyl->gas_volume(b).mliter;
 
 	/* milliliters per minute */
 	return lrint(airuse / atm * 60 / duration);
@@ -480,7 +481,8 @@ static int sac_between(const struct dive *dive, const struct plot_info &pi, int
 		a.mbar = get_plot_pressure(pi, first, i);
 		b.mbar = get_plot_pressure(pi, last, i);
 		const cylinder_t *cyl = dive->get_cylinder(i);
-		int cyluse = gas_volume(cyl, a) - gas_volume(cyl, b);
+		// TODO: Implement addition/subtraction on units.h types
+		int cyluse = cyl->gas_volume(a).mliter - cyl->gas_volume(b).mliter;
 		if (cyluse > 0)
 			airuse += cyluse;
 	}
@@ -1504,7 +1506,9 @@ std::vector<std::string> compare_samples(const struct dive *d, const struct plot
 
 					const cylinder_t *cyl = d->get_cylinder(cylinder_index);
 
-					volumes_used[cylinder_index] += gas_volume(cyl, (pressure_t){ last_pressures[cylinder_index] }) - gas_volume(cyl, (pressure_t){ next_pressure });
+					// TODO: Implement addition/subtraction on units.h types
+					volumes_used[cylinder_index] += cyl->gas_volume((pressure_t){ last_pressures[cylinder_index] }).mliter -
+									cyl->gas_volume((pressure_t){ next_pressure }).mliter;
 				}
 
 				// check if the gas in this cylinder is being used

core/statistics.cpp

@@ -258,8 +258,9 @@ std::vector<volume_t> get_gas_used(struct dive *dive)
 
 		start = cyl.start.mbar ? cyl.start : cyl.sample_start;
 		end = cyl.end.mbar ? cyl.end : cyl.sample_end;
+		// TODO: Implement addition/subtraction on units.h types
 		if (end.mbar && start.mbar > end.mbar)
-			gases[idx].mliter = gas_volume(&cyl, start) - gas_volume(&cyl, end);
+			gases[idx].mliter = cyl.gas_volume(start).mliter - cyl.gas_volume(end).mliter;
 		else
 			gases[idx].mliter = 0;
 	}

qt-models/cylindermodel.cpp

@@ -64,13 +64,13 @@ static QString get_cylinder_string(const cylinder_t *cyl)
 	return QString("%L1").arg(value, 0, 'f', decimals) + unit;
 }
 
-static QString gas_volume_string(int ml, const char *tail)
+static QString gas_volume_string(volume_t volume, const char *tail)
 {
 	double vol;
 	const char *unit;
 	int decimals;
 
-	vol = get_volume_units(ml, NULL, &unit);
+	vol = get_volume_units(volume.mliter, NULL, &unit);
 	decimals = (vol > 20.0) ? 0 : (vol > 2.0) ? 1 : 2;
 
 	return QString("%L1 %2 %3").arg(vol, 0, 'f', decimals).arg(unit).arg(tail);
@@ -83,13 +83,12 @@ static QVariant gas_usage_tooltip(const cylinder_t *cyl)
 	pressure_t startp = cyl->start.mbar ? cyl->start : cyl->sample_start;
 	pressure_t endp = cyl->end.mbar ? cyl->end : cyl->sample_end;
 
-	int start, end, used;
+	volume_t start = cyl->gas_volume(startp);
+	volume_t end = cyl->gas_volume(endp);
+	// TOOO: implement comparison and subtraction on units.h types.
+	volume_t used = (end.mliter && start.mliter > end.mliter) ? volume_t { start.mliter - end.mliter } : volume_t();
 
-	start = gas_volume(cyl, startp);
-	end = gas_volume(cyl, endp);
-	used = (end && start > end) ? start - end : 0;
-
-	if (!used)
+	if (!used.mliter)
 		return gas_wp_tooltip(cyl);
 
 	return gas_volume_string(used, "(") +
@@ -99,10 +98,10 @@ static QVariant gas_usage_tooltip(const cylinder_t *cyl)
 
 static QVariant gas_volume_tooltip(const cylinder_t *cyl, pressure_t p)
 {
-	int vol = gas_volume(cyl, p);
+	volume_t vol = cyl->gas_volume(p);
 	double Z;
 
-	if (!vol)
+	if (!vol.mliter)
 		return QVariant();
 
 	Z = gas_compressibility_factor(cyl->gasmix, p.mbar / 1000.0);