Make sample pressure helper functions available to everybody

We had a "add_sample_pressure()" helper functions that was local to just
the libdivecomputer downloading code, but it really is applicable to
pretty much any code that adds cylinder pressure data to a sample.

Also add another helper: "legacy_format_o2pressures()" which checks the
sample data to see if we can use the legacy format, and returns the o2
pressure sensor to use for that legacy format.

Because both the XML and the git save format will need a way to save the
compatible old-style information, when possible, but save an extended
format for when we have data from multiple concurrent sensors.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

1 files changed, 83 insertions, 0 deletions

diff --git a/core/dive.c b/core/dive.c
index 8270c5478..42ef687ef 100644
--- a/core/dive.c
+++ b/core/dive.c
@@ -35,6 +35,89 @@ const char *cylinderuse_text[] = {
 };
 const char *divemode_text[] = { "OC", "CCR", "PSCR", "Freedive" };
 
+/*
+ * 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
+ * indexes.
+ *
+ * The "prepare_sample()" function will always copy the sensor indices
+ * from the previous sample, so the indexes 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? */
+}
+
+/*
+ * The legacy format for sample pressures has a single pressure
+ * for each sample that can have any sensor, plus a possible
+ * "o2pressure" that is fixed to the Oxygen sensor for a CCR dive.
+ *
+ * For more complex pressure data, we have to use explicit
+ * cylinder indexes for each sample.
+ *
+ * This function returns a negative number for "no legacy mode",
+ * or a non-negative number that indicates the o2 sensor index.
+ */
+int legacy_format_o2pressures(struct dive *dive, struct divecomputer *dc)
+{
+	int i, o2sensor;
+
+	o2sensor = (dc->divemode == CCR) ? get_cylinder_idx_by_use(dive, OXYGEN) : -1;
+	for (i = 0; i < dc->samples; i++) {
+		struct sample *s = dc->sample + i;
+		int seen_pressure = 0, idx;
+
+		for (idx = 0; idx < MAX_SENSORS; idx++) {
+			int sensor = s->sensor[idx];
+			pressure_t p = s->pressure[idx];
+
+			if (!p.mbar)
+				continue;
+			if (sensor == o2sensor)
+				continue;
+			if (seen_pressure)
+				return -1;
+			seen_pressure = 1;
+		}
+	}
+
+	/*
+	 * Use legacy mode: if we have no O2 sensor we return a
+	 * positive sensor index that is guaranmteed to not match
+	 * any sensor (we encode it as 8 bits).
+	 */
+	return o2sensor < 0 ? 256 : o2sensor;
+}
+
 int event_is_gaschange(struct event *ev)
 {
 	return ev->type == SAMPLE_EVENT_GASCHANGE ||