Move mod calculations to a separate helper

We use mod calculations on multiple places, so make a separate helper
from it with proper types.

The "clumsiness" of defining a local variable to pass into the function
and out from it comes from the discrepancies in how c and c++ handles
initializations of variables in a struct.

Thanks goes to Tiago and Linus for pointing me in the right direction.

Signed-off-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

3 files changed, 11 insertions, 5 deletions

diff --git a/dive.h b/dive.h
index 05da2874b..fe2b5c784 100644
--- a/dive.h
+++ b/dive.h
@@ -104,6 +104,12 @@ static inline int interpolate(int a, int b, int part, int whole)
 	return rint(x / whole);
 }
 
+static inline depth_t gas_mod(struct gasmix *mix, pressure_t po2_limit) {
+	depth_t depth;
+	depth.mm = po2_limit.mbar * 1000 / get_o2(mix) * 10 - 10000;
+	return depth;
+}
+
 struct sample {
 	duration_t time;
 	depth_t depth;
diff --git a/profile.c b/profile.c
index fea03308d..26b267dd0 100644
--- a/profile.c
+++ b/profile.c
@@ -1155,7 +1155,8 @@ static void calculate_gas_information_new(struct dive *dive, struct plot_info *p
 		 * so there is no difference in calculating between OC and CC
 		 * END takes O2 + N2 (air) into account ("Narcotic" for trimix dives)
 		 * EAD just uses N2 ("Air" for nitrox dives) */
-		entry->mod = (prefs.modppO2 / fo2 * 1000 - 1) * 10000;
+		pressure_t modppO2 = { .mbar = (int) (prefs.modppO2 * 1000) };
+		entry->mod = (double) gas_mod(&dive->cylinder[cylinderindex].gasmix, modppO2).mm;
 		entry->end = (entry->depth + 10000) * (1000 - fhe) / 1000.0 - 10000;
 		entry->ead = (entry->depth + 10000) * (1000 - fo2 - fhe) / (double)N2_IN_AIR - 10000;
 		entry->eadd = (entry->depth + 10000) *
diff --git a/qt-ui/diveplanner.cpp b/qt-ui/diveplanner.cpp
index aaf530ca7..3ffacdd2b 100644
--- a/qt-ui/diveplanner.cpp
+++ b/qt-ui/diveplanner.cpp
@@ -499,10 +499,9 @@ bool DivePlannerPointsModel::addGas(int o2, int he)
 			cyl->gasmix.he.permille = he;
 			/* The depth to change to that gas is given by the depth where its pO2 is 1.6 bar.
 			 * The user should be able to change this depth manually. */
-			if (!o2)
-				cyl->depth.mm = 1600 * 1000 / O2_IN_AIR * 10 - 10000;
-			else
-				cyl->depth.mm = 1600 * 1000 / o2 * 10 - 10000;
+			pressure_t modppO2;
+			modppO2.mbar = 1600;
+			cyl->depth = gas_mod(&cyl->gasmix, modppO2);
 			CylindersModel::instance()->setDive(stagingDive);
 			return true;
 		}