1 files changed, 57 insertions, 0 deletions
diff --git a/core/gas.h b/core/gas.h
new file mode 100644
index 000000000..f5d948da0
--- /dev/null
+++ b/core/gas.h
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef GAS_H
+#define GAS_H
+
+#include "units.h"
+
+#ifdef __cplusplus
+extern "C" {
+#else
+#include <stdbool.h>
+#endif
+
+// o2 == 0 && he == 0 -> air
+// o2 < 0 -> invalid
+struct gasmix {
+	fraction_t o2;
+	fraction_t he;
+};
+static const struct gasmix gasmix_invalid = { { -1 }, { -1 } };
+static const struct gasmix gasmix_air = { { 0 }, { 0 } };
+
+struct icd_data { // This structure provides communication between function isobaric_counterdiffusion() and the calling software.
+	int dN2;      // The change in fraction (permille) of nitrogen during the change
+	int dHe;      // The change in fraction (permille) of helium during the change
+};
+
+extern bool isobaric_counterdiffusion(struct gasmix oldgasmix, struct gasmix newgasmix, struct icd_data *results);
+
+extern double gas_compressibility_factor(struct gasmix gas, double bar);
+extern double isothermal_pressure(struct gasmix gas, double p1, int volume1, int volume2);
+extern double gas_density(struct gasmix gas, int pressure);
+extern int same_gasmix(struct gasmix a, struct gasmix b);
+
+static inline int get_o2(struct gasmix mix)
+{
+	return mix.o2.permille ?: O2_IN_AIR;
+}
+
+static inline int get_he(struct gasmix mix)
+{
+	return mix.he.permille;
+}
+
+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 bool gasmix_is_air(struct gasmix gasmix);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif