Further cleanup of pressure and volume conversions

I'm amazed at how many spots we were doing conversions - some of them
subtly different than others.

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

2 files changed, 38 insertions, 22 deletions

diff --git a/dive.h b/dive.h
index fe4515ee6..783d640a0 100644
--- a/dive.h
+++ b/dive.h
@@ -91,9 +91,19 @@ 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 bar_to_atm(double bar)
+{
+	return bar / 1.01325;
+}
+
 static inline double ml_to_cuft(int ml)
 {
-	return ml / 28317.0;
+	return ml / 28316.8466;
+}
+
+static inline double cuft_to_ml(double cuft)
+{
+	return cuft * 28.3168466;
 }
 
 static inline double mm_to_feet(int mm)
@@ -137,6 +147,10 @@ static inline int to_K(temperature_t temp)
 	return (temp.mkelvin + 499)/1000;
 }
 
+static inline double psi_to_bar(double psi)
+{
+	return psi / 14.5037738;
+}
 static inline int to_PSI(pressure_t pressure)
 {
 	return pressure.mbar * 0.0145037738 + 0.5;
diff --git a/equipment.c b/equipment.c
index 12f39ae3f..64a05d5b0 100644
--- a/equipment.c
+++ b/equipment.c
@@ -49,18 +49,19 @@ struct cylinder_widget {
 	GtkWidget *o2, *gasmix_button;
 };
 
+/* we want bar - so let's not use our unit functions */
 static int convert_pressure(int mbar, double *p)
 {
 	int decimals = 1;
 	double pressure;
 
-	pressure = mbar / 1000.0;
-	if (mbar) {
-		if (output_units.pressure == PSI) {
-			pressure *= 14.5037738;	/* Bar to PSI */
-			decimals = 0;
-		}
+	if (output_units.pressure == PSI) {
+		pressure = mbar_to_PSI(mbar);
+		decimals = 0;
+	} else {
+		pressure = mbar / 1000.0;
 	}
+
 	*p = pressure;
 	return decimals;
 }
@@ -70,17 +71,18 @@ static int convert_volume_pressure(int ml, int mbar, double *v, double *p)
 	int decimals = 1;
 	double volume, pressure;
 
-	volume = ml / 1000.0;
-	pressure = mbar / 1000.0;
 	if (mbar) {
 		if (output_units.volume == CUFT) {
-			volume /= 28.3168466;	/* Liters to cuft */
-			volume *= pressure / 1.01325;
-		}
+			volume = ml_to_cuft(ml);
+			volume *= bar_to_atm(mbar / 1000.0);
+		} else
+			volume = ml / 1000.0;
+
 		if (output_units.pressure == PSI) {
-			pressure *= 14.5037738;	/* Bar to PSI */
+			pressure = mbar_to_PSI(mbar);
 			decimals = 0;
-		}
+		} else
+			pressure = mbar / 1000.0;
 	}
 	*v = volume;
 	*p = pressure;
@@ -352,14 +354,14 @@ static void fill_cylinder_info(struct cylinder_widget *cylinder, cylinder_t *cyl
 	int mbar, ml;
 
 	if (output_units.pressure == PSI) {
-		pressure /= 14.5037738;
-		start /= 14.5037738;
-		end /= 14.5037738;
+		pressure = psi_to_bar(pressure);
+		start = psi_to_bar(start);
+		end = psi_to_bar(end);
 	}
 
 	if (pressure && output_units.volume == CUFT) {
-		volume *= 28.3168466;	/* CUFT to liter */
-		volume /= pressure / 1.01325;
+		volume = cuft_to_ml(volume);
+		volume /= bar_to_atm(pressure);
 	}
 
 	ml = volume * 1000 + 0.5;
@@ -461,9 +463,9 @@ static void fill_tank_list(GtkListStore *store)
 
 		/* Is it in cuft and psi? */
 		if (psi) {
-			double bar = 0.0689475729 * psi;
-			double airvolume = 28316.8466 * size;
-			double atm = bar / 1.01325;
+			double bar = psi_to_bar(psi);
+			double airvolume = cuft_to_ml(size);
+			double atm = bar_to_atm(bar);
 
 			ml = airvolume / atm + 0.5;
 			mbar = bar*1000 + 0.5;