More consistency improvements

Treat SAC and OTU consistently:
- SAC is now a member of struct dive
- it's calculated / populated at the same time with a helper function with
  consistent API

Create get_volume_units function that returns volumes (e.g. used in SAC
rates) based on preferred units - make sure we have these conversions just
once in the code.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

dive.c

@@ -46,6 +46,31 @@ double get_temp_units(unsigned int mk, const char **units)
 	return deg;
 }
 
+double get_volume_units(unsigned int ml, int *frac, const char **units)
+{
+	int decimals;
+	double vol;
+	const char *unit;
+
+	switch (output_units.volume) {
+	case LITER:
+		vol = ml / 1000.0;
+		unit = "l";
+		decimals = 1;
+		break;
+	case CUFT:
+		vol = ml_to_cuft(ml);
+		unit = "cuft";
+		decimals = 2;
+		break;
+	}
+	if (frac)
+		*frac = decimals;
+	if (units)
+		*units = unit;
+	return vol;
+}
+
 double get_depth_units(unsigned int mm, int *frac, const char **units)
 {
 	int decimals;

dive.h

@@ -87,8 +87,14 @@ typedef struct {
 } cylinder_t;
 
 extern double get_depth_units(unsigned int mm, int *frac, const char **units);
+extern double get_volume_units(unsigned int mm, int *frac, const char **units);
 extern double get_temp_units(unsigned int mm, const char **units);
 
+static inline double ml_to_cuft(int ml)
+{
+	return ml / 28317.0;
+}
+
 static inline double mm_to_feet(int mm)
 {
 	return mm * 0.00328084;
@@ -177,7 +183,7 @@ struct dive {
 	depth_t visibility;
 	temperature_t airtemp, watertemp;
 	cylinder_t cylinder[MAX_CYLINDERS];
-	int otu;
+	int sac, otu;
 	struct event *events;
 	int samples, alloc_samples;
 	struct sample sample[];

divelist.c

@@ -315,23 +315,22 @@ static double calculate_airuse(struct dive *dive)
 	return airuse;
 }
 
-static void get_sac(struct dive *dive, int *val)
+static int calculate_sac(struct dive *dive)
 {
 	double airuse, pressure, sac;
 
-	*val = 0;
 	airuse = calculate_airuse(dive);
 	if (!airuse)
-		return;
+		return 0;
 	if (!dive->duration.seconds)
-		return;
+		return 0;
 
 	/* Mean pressure in atm: 1 atm per 10m */
 	pressure = 1 + (dive->meandepth.mm / 10000.0);
 	sac = airuse / pressure * 60 / dive->duration.seconds;
 
 	/* milliliters per minute.. */
-	*val = sac * 1000;
+	return sac * 1000;
 }
 
 static void get_string(char **str, const char *s)
@@ -364,12 +363,10 @@ static void fill_one_dive(struct dive *dive,
 			  GtkTreeModel *model,
 			  GtkTreeIter *iter)
 {
-	int sac;
 	char *location, *cylinder;
 
 	get_cylinder(dive, &cylinder);
 	get_location(dive, &location);
-	get_sac(dive, &sac);
 
 	/*
 	 * We only set the fields that changed: the strings.
@@ -379,7 +376,7 @@ static void fill_one_dive(struct dive *dive,
 		DIVE_NR, dive->number,
 		DIVE_LOCATION, location,
 		DIVE_CYLINDER, cylinder,
-		DIVE_SAC, sac,
+		DIVE_SAC, dive->sac,
 		DIVE_OTU, dive->otu,
 		-1);
 }
@@ -471,6 +468,7 @@ static void fill_dive_list(void)
 		struct dive *dive = dive_table.dives[i];
 
 		dive->otu = calculate_otu(dive);
+		dive->sac = calculate_sac(dive);
 		gtk_list_store_append(store, &iter);
 		gtk_list_store_set(store, &iter,
 			DIVE_INDEX, i,