CCR code: Split profile.c into two files, with gas caluclations separate.

This patch implements a separation of the code for gas pressure
calculations from the rest of the code in profile.c. The latter
file is now split into: profile.c and gaspressures.c. The
details of the transferred functions is given at the top of
gaspressures.c. The following chnages were made:
1) dive.h: The function types of calculate_depth_to_mbar
   and depth_to_mbar were made non-static in order to make them
   available within gaspressures.c.
2) profile.c: Prototypes for the functions in gaspressures.c
   were inserted at the top of profile. Ten functions were
   transferred from profile.c to gaspressures.c
3) gaspressures.c as well as a short header, gaspressures.h
   were created.

For the gas pressure calculations for CCR dives, gaspressures.c
forms the immediate basis for further code development.

Signed-off-by: Willem Ferguson <willemferguson@zoology.up.ac.za>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

1 files changed, 347 insertions, 0 deletions

diff --git a/gaspressures.c b/gaspressures.c
new file mode 100644
index 000000000..b14264a3b
--- /dev/null
+++ b/gaspressures.c
@@ -0,0 +1,347 @@
+/*  gaspressures.c
+ *  ---------------
+ *  This file contains the routines to calculate the gas pressures in the cylinders.
+ *  The functions below support the code in profile.c.
+ *  The high-level function is populate_pressure_information(), called by function
+ *  create_plot_info_new() in profile.c. The other functions below are, in turn,
+ *  called by populate_pressure_information(). The calling sequence is as follows:
+ *
+ *  populate_pressure_information() -> calc_pressure_time()
+ *                                  -> fill_missing_tank_pressures() -> fill_missing_segment_pressures()
+ *                                                                   -> get_pr_interpolate_data()
+ */
+
+#include "gettext.h"
+#include <limits.h>
+#include <string.h>
+
+#include "dive.h"
+#include "display.h"
+#include "divelist.h"
+
+#include "profile.h"
+#include "gaspressures.h"
+#include "deco.h"
+#include "libdivecomputer/parser.h"
+#include "libdivecomputer/version.h"
+#include "membuffer.h"
+
+
+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->end = 0;
+	pt->t_start = pt->t_end = t_start;
+	pt->pressure_time = 0;
+	pt->next = NULL;
+	return pt;
+}
+
+/* poor man's linked list */
+static pr_track_t *list_last(pr_track_t *list)
+{
+	pr_track_t *tail = list;
+	if (!tail)
+		return NULL;
+	while (tail->next) {
+		tail = tail->next;
+	}
+	return tail;
+}
+
+static pr_track_t *list_add(pr_track_t *list, pr_track_t *element)
+{
+	pr_track_t *tail = list_last(list);
+	if (!tail)
+		return element;
+	tail->next = element;
+	return list;
+}
+
+static void list_free(pr_track_t *list)
+{
+	if (!list)
+		return;
+	list_free(list->next);
+	free(list);
+}
+
+#ifdef DEBUG_PR_TRACK
+static void dump_pr_track(pr_track_t **track_pr)
+{
+	int cyl;
+	pr_track_t *list;
+
+	for (cyl = 0; cyl < MAX_CYLINDERS; cyl++) {
+		list = track_pr[cyl];
+		while (list) {
+			printf("cyl%d: start %d end %d t_start %d t_end %d pt %d\n", cyl,
+			       list->start, list->end, list->t_start, list->t_end, list->pressure_time);
+			list = list->next;
+		}
+	}
+}
+#endif
+
+/*
+ * This looks at the pressures for one cylinder, and
+ * calculates any missing beginning/end pressures for
+ * each segment by taking the over-all SAC-rate into
+ * account for that cylinder.
+ *
+ * NOTE! Many segments have full pressure information
+ * (both beginning and ending pressure). But if we have
+ * switched away from a cylinder, we will have the
+ * beginning pressure for the first segment with a
+ * missing end pressure. We may then have one or more
+ * segments without beginning or end pressures, until
+ * we finally have a segment with an end pressure.
+ *
+ * We want to spread out the pressure over these missing
+ * segments according to how big of a time_pressure area
+ * they have.
+ */
+void fill_missing_segment_pressures(pr_track_t *list)
+{
+	while (list) {
+		int start = list->start, end;
+		pr_track_t *tmp = list;
+		int pt_sum = 0, pt = 0;
+
+		for (;;) {
+			pt_sum += tmp->pressure_time;
+			end = tmp->end;
+			if (end)
+				break;
+			end = start;
+			if (!tmp->next)
+				break;
+			tmp = tmp->next;
+		}
+
+		if (!start)
+			start = end;
+
+		/*
+		 * Now 'start' and 'end' contain the pressure values
+		 * for the set of segments described by 'list'..'tmp'.
+		 * pt_sum is the sum of all the pressure-times of the
+		 * segments.
+		 *
+		 * Now dole out the pressures relative to pressure-time.
+		 */
+		list->start = start;
+		tmp->end = end;
+		for (;;) {
+			int pressure;
+			pt += list->pressure_time;
+			pressure = start;
+			if (pt_sum)
+				pressure -= (start - end) * (double)pt / pt_sum;
+			list->end = pressure;
+			if (list == tmp)
+				break;
+			list = list->next;
+			list->start = pressure;
+		}
+
+		/* Ok, we've done that set of segments */
+		list = list->next;
+	}
+}
+
+#ifdef DEBUG_PR_INTERPOLATE
+void dump_pr_interpolate(int i, pr_interpolate_t interpolate_pr)
+{
+	printf("Interpolate for entry %d: start %d - end %d - pt %d - acc_pt %d\n", i,
+	       interpolate_pr.start, interpolate_pr.end, interpolate_pr.pressure_time, interpolate_pr.acc_pressure_time);
+}
+#endif
+
+
+struct pr_interpolate_struct get_pr_interpolate_data(pr_track_t *segment, struct plot_info *pi, int cur)
+{
+	struct pr_interpolate_struct interpolate;
+	int i;
+	struct plot_data *entry;
+
+	interpolate.start = segment->start;
+	interpolate.end = segment->end;
+	interpolate.acc_pressure_time = 0;
+	interpolate.pressure_time = 0;
+
+	for (i = 0; i < pi->nr; i++) {
+		entry = pi->entry + i;
+		if (entry->sec < segment->t_start)
+			continue;
+		if (entry->sec >= segment->t_end) {
+			interpolate.pressure_time += entry->pressure_time;
+			break;
+		}
+		if (entry->sec == segment->t_start) {
+			interpolate.acc_pressure_time = 0;
+			interpolate.pressure_time = 0;
+			if (SENSOR_PRESSURE(entry))
+				interpolate.start = SENSOR_PRESSURE(entry);
+			continue;
+		}
+		if (i < cur) {
+			if (SENSOR_PRESSURE(entry)) {
+				interpolate.start = SENSOR_PRESSURE(entry);
+				interpolate.acc_pressure_time = 0;
+				interpolate.pressure_time = 0;
+			} else {
+				interpolate.acc_pressure_time += entry->pressure_time;
+				interpolate.pressure_time += entry->pressure_time;
+			}
+			continue;
+		}
+		if (i == cur) {
+			interpolate.acc_pressure_time += entry->pressure_time;
+			interpolate.pressure_time += entry->pressure_time;
+			continue;
+		}
+		interpolate.pressure_time += entry->pressure_time;
+		if (SENSOR_PRESSURE(entry)) {
+			interpolate.end = SENSOR_PRESSURE(entry);
+			break;
+		}
+	}
+	return interpolate;
+}
+
+void fill_missing_tank_pressures(struct dive *dive, struct plot_info *pi, pr_track_t **track_pr)
+{
+	int cyl, i;
+	struct plot_data *entry;
+	int cur_pr[MAX_CYLINDERS];
+
+#ifdef DEBUG_PR_TRACK
+	/* another great debugging tool */
+	dump_pr_track(track_pr);
+#endif
+	for (cyl = 0; cyl < MAX_CYLINDERS; cyl++) {
+		if (!track_pr[cyl]) {
+			/* no segment where this cylinder is used */
+			cur_pr[cyl] = -1;
+			continue;
+		}
+		fill_missing_segment_pressures(track_pr[cyl]);
+		cur_pr[cyl] = track_pr[cyl]->start;
+	}
+
+	/* The first two are "fillers", but in case we don't have a sample
+	 * at time 0 we need to process the second of them here */
+	for (i = 1; i < pi->nr; i++) {
+		double magic;
+		pr_track_t *segment;
+		pr_interpolate_t interpolate;
+
+		entry = pi->entry + i;
+		cyl = entry->cylinderindex;
+
+		if (SENSOR_PRESSURE(entry)) {
+			cur_pr[cyl] = SENSOR_PRESSURE(entry);
+			continue;
+		}
+
+		/* Find the right pressure segment for this entry.. */
+		segment = track_pr[cyl];
+		while (segment && segment->t_end < entry->sec)
+			segment = segment->next;
+
+		/* No (or empty) segment? Just use our current pressure */
+		if (!segment || !segment->pressure_time) {
+			SENSOR_PRESSURE(entry) = cur_pr[cyl];
+			continue;
+		}
+
+		interpolate = get_pr_interpolate_data(segment, pi, i);
+#ifdef DEBUG_PR_INTERPOLATE
+		dump_pr_interpolate(i, interpolate);
+#endif
+		/* if this segment has pressure time, calculate a new interpolated pressure */
+		if (interpolate.pressure_time) {
+			/* Overall pressure change over total pressure-time for this segment*/
+			magic = (interpolate.end - interpolate.start) / (double)interpolate.pressure_time;
+
+			/* Use that overall pressure change to update the current pressure */
+			cur_pr[cyl] = rint(interpolate.start + magic * interpolate.acc_pressure_time);
+		}
+		INTERPOLATED_PRESSURE(entry) = cur_pr[cyl];
+	}
+}
+
+/*
+ * What's the pressure-time between two plot data entries?
+ * We're calculating the integral of pressure over time by
+ * adding these up.
+ *
+ * The units won't matter as long as everybody agrees about
+ * them, since they'll cancel out - we use this to calculate
+ * a constant SAC-rate-equivalent, but we only use it to
+ * scale pressures, so it ends up being a unitless scaling
+ * factor.
+ */
+inline int calc_pressure_time(struct dive *dive, struct divecomputer *dc, struct plot_data *a, struct plot_data *b)
+{
+	int time = b->sec - a->sec;
+	int depth = (a->depth + b->depth) / 2;
+
+	if (depth <= SURFACE_THRESHOLD)
+		return 0;
+
+	return depth_to_mbar(depth, dive) * time;
+}
+
+void populate_pressure_information(struct dive *dive, struct divecomputer *dc, struct plot_info *pi)
+{
+	int i, cylinderindex;
+	pr_track_t *track_pr[MAX_CYLINDERS] = { NULL, };
+	pr_track_t *current;
+	bool missing_pr = false;
+
+	cylinderindex = -1;
+	current = NULL;
+	for (i = 0; i < pi->nr; i++) {
+		struct plot_data *entry = pi->entry + i;
+		int pressure = SENSOR_PRESSURE(entry);
+
+		/* discrete integration of pressure over time to get the SAC rate equivalent */
+		if (current) {
+			entry->pressure_time = calc_pressure_time(dive, dc, entry - 1, entry);
+			current->pressure_time += entry->pressure_time;
+			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(pressure, entry->sec);
+			track_pr[cylinderindex] = list_add(track_pr[cylinderindex], current);
+			continue;
+		}
+
+		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) {
+		fill_missing_tank_pressures(dive, pi, track_pr);
+	}
+	for (i = 0; i < MAX_CYLINDERS; i++)
+		list_free(track_pr[i]);
+}