cleanup: split out divecomputer functions from dive.c

Since dive.c is so huge, split out divecomputer-related functions
into divecomputer.[c|h], sample.[c|h] and extradata.[c|h].

This does not give huge compile time improvements, since
struct dive contains a struct divecomputer and therefore
dive.h has to include divecomputer.h. However, it make things
distinctly more clear.

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

core/sample.c

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "sample.h"
+
+/*
+ * Adding a cylinder pressure sample field is not quite as trivial as it
+ * perhaps should be.
+ *
+ * We try to keep the same sensor index for the same sensor, so that even
+ * if the dive computer doesn't give pressure information for every sample,
+ * we don't move pressure information around between the different sensor
+ * indices.
+ *
+ * The "prepare_sample()" function will always copy the sensor indices
+ * from the previous sample, so the indices are pre-populated (but the
+ * pressures obviously are not)
+ */
+void add_sample_pressure(struct sample *sample, int sensor, int mbar)
+{
+	int idx;
+
+	if (!mbar)
+		return;
+
+	/* Do we already have a slot for this sensor */
+	for (idx = 0; idx < MAX_SENSORS; idx++) {
+		if (sensor != sample->sensor[idx])
+			continue;
+		sample->pressure[idx].mbar = mbar;
+		return;
+	}
+
+	/* Pick the first unused index if we couldn't reuse one */
+	for (idx = 0; idx < MAX_SENSORS; idx++) {
+		if (sample->pressure[idx].mbar)
+			continue;
+		sample->sensor[idx] = sensor;
+		sample->pressure[idx].mbar = mbar;
+		return;
+	}
+
+	/* We do not have enough slots for the pressure samples. */
+	/* Should we warn the user about dropping pressure data? */
+}
+