[PATCH] Fix cylinder pressure interpolation

[Linus Torvalds]

From: Linus Torvalds <torvalds at linux-foundation.org>
Date: Thu, 28 Mar 2013 12:03:00 -0700
Subject: [PATCH] Fix cylinder pressure interpolation

The pressure interpolation code mostly worked for the simple cases, but
got terminally confused for some more complex gas change situations,
resulting in nonsensical interpolations.

This simplifies and clarifies the code a bit, and in the process fixes a
few special cases where the gas interpolation segments didn't end up
having the end conditions set.

Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
---

Ok, this removes more lines than it adds, simplifies the code a bit, and 
should fix the cylinder pressure interpolation problem that the 
rather "special" Petrel gaschange events exposed.

WorksForMe(tm).

With this, and the previous series of three patches, I can now load the 
Uemis and Petrel dives that Dirk had, and the merged data not only makes 
sense, but the profiles look correct for both dive computers.

 profile.c | 63 ++++++++++++++++++++++++++-------------------------------------
 1 file changed, 26 insertions(+), 37 deletions(-)

diff --git a/profile.c b/profile.c
index 59c6485a95f8..18960fcff265 100644
--- a/profile.c
+++ b/profile.c
@@ -1316,9 +1316,8 @@ struct pr_track_struct {
 static pr_track_t *pr_track_alloc(int start, int t_start) {
 	pr_track_t *pt = malloc(sizeof(pr_track_t));
 	pt->start = start;
-	pt->t_start = t_start;
 	pt->end = 0;
-	pt->t_end = 0;
+	pt->t_start = pt->t_end = t_start;
 	pt->pressure_time = 0;
 	pt->next = NULL;
 	return pt;
@@ -1465,6 +1464,8 @@ static void fill_missing_tank_pressures(struct dive *dive, struct plot_info *pi,
 		dump_pr_track(track_pr);
 	}
 	for (cyl = 0; cyl < MAX_CYLINDERS; cyl++) {
+		if (!track_pr[cyl])
+			continue;
 		fill_missing_segment_pressures(track_pr[cyl]);
 		cur_pr[cyl] = track_pr[cyl]->start;
 	}
@@ -1809,52 +1810,40 @@ static void populate_pressure_information(struct dive *dive, struct divecomputer
 	pr_track_t *current;
 	gboolean missing_pr = FALSE;
 
-	/* Set up the pressure tracking data structures */
-	for (i = 0; i < MAX_CYLINDERS; i++) {
-		cylinder_t *cyl = dive->cylinder + i;
-		int mbar = cyl->start.mbar ? : cyl->sample_start.mbar;
-		track_pr[i] = pr_track_alloc(mbar, 0);
-	}
-
-	cylinderindex = pi->entry[0].cylinderindex;
-	current = track_pr[cylinderindex];
-	for (i = 1; i < pi->nr; i++) {
+	cylinderindex = -1;
+	current = NULL;
+	for (i = 0; i < pi->nr; i++) {
 		struct plot_data *entry = pi->entry + i;
+		unsigned pressure = SENSOR_PRESSURE(entry);
 
 		/* discrete integration of pressure over time to get the SAC rate equivalent */
-		current->pressure_time += pressure_time(dive, dc, entry-1, entry);
+		if (current) {
+			current->pressure_time += pressure_time(dive, dc, entry-1, entry);
+			current->t_end = entry->sec;
+		}
 
 		/* track the segments per cylinder and their pressure/time integral */
 		if (entry->cylinderindex != cylinderindex) {
 			cylinderindex = entry->cylinderindex;
-			current = pr_track_alloc(SENSOR_PRESSURE(entry), entry->sec);
+			current = pr_track_alloc(pressure, entry->sec);
 			track_pr[cylinderindex] = list_add(track_pr[cylinderindex], current);
-		} else { /* same cylinder */
-			if (SENSOR_PRESSURE(entry) && !SENSOR_PRESSURE(entry-1)) {
-				/* transmitter changed its working status */
-				current->end = SENSOR_PRESSURE(entry);
-				current->t_end = entry->sec;
-				current = pr_track_alloc(SENSOR_PRESSURE(entry), entry->sec);
-				track_pr[cylinderindex] =
-					list_add(track_pr[cylinderindex], current);
-			}
-		}
-		/* finally, do the discrete integration to get the SAC rate equivalent */
-		if (SENSOR_PRESSURE(entry)) {
-			current->end = SENSOR_PRESSURE(entry);
-			current->t_end = entry->sec;
+			continue;
 		}
-		missing_pr |= !SENSOR_PRESSURE(entry);
-	}
 
-	/* initialize the end pressures */
-	for (i = 0; i < MAX_CYLINDERS; i++) {
-		cylinder_t *cyl = dive->cylinder + i;
-		int pr = cyl->end.mbar ? : cyl->sample_end.mbar;
-		if (pr && track_pr[i]) {
-			pr_track_t *pr_track = list_last(track_pr[i]);
-			pr_track->end = pr;
+		if (!pressure) {
+			missing_pr = 1;
+			continue;
 		}
+
+		current->end = pressure;
+
+		/* Was it continuous? */
+		if (SENSOR_PRESSURE(entry-1))
+			continue;
+
+		/* transmitter changed its working status */
+		current = pr_track_alloc(pressure, entry->sec);
+		track_pr[cylinderindex] = list_add(track_pr[cylinderindex], current);
 	}
 
 	if (missing_pr) {
-- 
1.8.2.230.g2bba2f0