Fix ATM-vs-bar confusion

SAC should be calculated in relationship to surface pressure, not "1 bar".

I also realize that we have a few other cases where we do the same
mistake: the partial pressure calculations do things like

    po2 = o2 / 1000.0 * depth_to_mbar(sample->depth.mm, dive);

which is wrong as well - the partial pressure is also relative to
standard atmospheric pressures.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/dive.h b/dive.h
index 7d0aaaee6..658b199fe 100644
--- a/dive.h
+++ b/dive.h
@@ -223,6 +223,11 @@ static inline double bar_to_atm(double bar)
 	return bar / SURFACE_PRESSURE * 1000;
 }
 
+static inline double mbar_to_atm(int mbar)
+{
+	return (double) mbar / SURFACE_PRESSURE;
+}
+
 /* Volume in mliter of a cylinder at pressure 'p' */
 extern int gas_volume(cylinder_t *cyl, pressure_t p);
 extern int wet_volume(double cuft, pressure_t p);
@@ -450,6 +455,11 @@ static inline int depth_to_mbar(int depth, struct dive *dive)
 	return calculate_depth_to_mbar(depth, dive->surface_pressure, dive->salinity);
 }
 
+static inline double depth_to_atm(int depth, struct dive *dive)
+{
+	return mbar_to_atm(depth_to_mbar(depth, dive));
+}
+
 /* for the inverse calculation we use just the relative pressure
  * (that's the one that some dive computers like the Uemis Zurich
  * provide - for the other models that do this libdivecomputer has to