core: convert sample.c to C++ and add default constructor

This changes default behavior when creating a sample struct
in C++ code: it is now initialized to default values. If this
ever turns out to be a performance problem, we can either add
additional constructors or use special functions that do
not initialize memory, such as make_unique_for_overwrite.

This removes non-standard (respectively >C++20) constructs,
namely designated initializers.

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

core/sample.cpp

@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "sample.h"
+
+sample::sample() :
+	time({ 0 }),
+	stoptime({ 0 }),
+	ndl({ -1 }),
+	tts({ 0 }),
+	rbt({ 0 }),
+	depth({ 0 }),
+	stopdepth({ 0 }),
+	temperature({ 0 }),
+	pressure { { 0 }, { 0 } },
+	setpoint({ 0 }),
+	o2sensor { { 0 }, { 0 }, { 0 }, { 0 }, { 0 }, { 0 } },
+	bearing({ -1 }),
+	sensor { 0, 0 },
+	cns(0),
+	heartbeat(0),
+	sac({ 0 }),
+	in_deco(false),
+	manually_entered(false)
+{
+}
+
+/*
+ * 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)
+ */
+extern "C" 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? */
+}