Cleanup: move gas-functions to own translation unit

But only functions that operate only on gases. Functions concerning
cylinders or dives remain in dive.c or are moved to equipment.c

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

1 files changed, 79 insertions, 0 deletions

diff --git a/core/gas.c b/core/gas.c
new file mode 100644
index 000000000..9f67d0b92
--- /dev/null
+++ b/core/gas.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "gas.h"
+#include "pref.h"
+#include <stdio.h>
+#include <string.h>
+
+/* Perform isobaric counterdiffusion calculations for gas changes in trimix dives.
+ * Here we use the rule-of-fifths where, during a change involving trimix gas, the increase in nitrogen
+ * should not exceed one fifth of the decrease in helium.
+ * Parameters: 1) pointers to two gas mixes, the gas being switched from and the gas being switched to.
+ *             2) a pointer to an icd_data structure.
+ * Output:     i) The icd_data stucture is filled with the delta_N2 and delta_He numbers (as permille).
+ *            ii) Function returns a boolean indicating an exceeding of the rule-of-fifths. False = no icd problem.
+ */
+bool isobaric_counterdiffusion(struct gasmix oldgasmix, struct gasmix newgasmix, struct icd_data *results)
+{
+	if (!prefs.show_icd)
+		return false;
+	results->dN2 = get_he(oldgasmix) + get_o2(oldgasmix) - get_he(newgasmix) - get_o2(newgasmix);
+	results->dHe = get_he(newgasmix) - get_he(oldgasmix);
+	return get_he(oldgasmix) > 0 && results->dN2 > 0 && results->dHe < 0 && get_he(oldgasmix) && results->dN2 > 0 && 5 * results->dN2 > -results->dHe;
+}
+
+static bool gasmix_is_invalid(struct gasmix mix)
+{
+	return mix.o2.permille < 0;
+}
+
+int same_gasmix(struct gasmix a, struct gasmix b)
+{
+	if (gasmix_is_invalid(a) || gasmix_is_invalid(b))
+		return 0;
+	if (gasmix_is_air(a) && gasmix_is_air(b))
+		return 1;
+	return a.o2.permille == b.o2.permille && a.he.permille == b.he.permille;
+}
+
+void sanitize_gasmix(struct gasmix *mix)
+{
+	unsigned int o2, he;
+
+	o2 = mix->o2.permille;
+	he = mix->he.permille;
+
+	/* Regular air: leave empty */
+	if (!he) {
+		if (!o2)
+			return;
+		/* 20.8% to 21% O2 is just air */
+		if (gasmix_is_air(*mix)) {
+			mix->o2.permille = 0;
+			return;
+		}
+	}
+
+	/* Sane mix? */
+	if (o2 <= 1000 && he <= 1000 && o2 + he <= 1000)
+		return;
+	fprintf(stderr, "Odd gasmix: %u O2 %u He\n", o2, he);
+	memset(mix, 0, sizeof(*mix));
+}
+
+int gasmix_distance(struct gasmix a, struct gasmix b)
+{
+	int a_o2 = get_o2(a), b_o2 = get_o2(b);
+	int a_he = get_he(a), b_he = get_he(b);
+	int delta_o2 = a_o2 - b_o2, delta_he = a_he - b_he;
+
+	delta_he = delta_he * delta_he;
+	delta_o2 = delta_o2 * delta_o2;
+	return delta_he + delta_o2;
+}
+
+bool gasmix_is_air(struct gasmix gasmix)
+{
+	int o2 = gasmix.o2.permille;
+	int he = gasmix.he.permille;
+	return (he == 0) && (o2 == 0 || ((o2 >= O2_IN_AIR - 1) && (o2 <= O2_IN_AIR + 1)));
+}