core: add N2 and general gas component accessors

There were helper functions to access O2 and He component fractions.
Add another one for N2. Indeed, this can be used in three cases, where
N2 was deduced indirectly.

Moreover, add a general accessor with a gas_component argument.
This will be used by the filter code to filter for gas components.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/core/gas.h b/core/gas.h
index 316f4d3de..c5db7eeff 100644
--- a/core/gas.h
+++ b/core/gas.h
@@ -43,12 +43,18 @@ static inline int get_he(struct gasmix mix)
 	return mix.he.permille;
 }
 
+static inline int get_n2(struct gasmix mix)
+{
+	return 1000 - get_o2(mix) - get_he(mix);
+}
+
 struct gas_pressures {
 	double o2, n2, he;
 };
 
 extern void sanitize_gasmix(struct gasmix *mix);
 extern int gasmix_distance(struct gasmix a, struct gasmix b);
+extern fraction_t get_gas_component_fraction(struct gasmix mix, enum gas_component component);
 
 extern bool gasmix_is_air(struct gasmix gasmix);