Look for actual isobaric counter diffusion

Identify segements that fullfill the folllowing criteria for
the leading compartment:

He is off-gasing while N2 is on-gasing
Overall there is on-gasing

Add a line to the info box for those segments

Signed-off-by: Robert C. Helling <helling@atdotde.de>

5 files changed, 14 insertions, 2 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index da4359901..550b616d4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,4 @@
+- Profile: Add information about actual isobaric counter diffusion happening
 - Suunto DM import: improved temperature parsing in special cases
 # Always add new entries at the very top of this file above other
 # existing entries.
diff --git a/core/deco.c b/core/deco.c
index 9943d470f..f72454b9b 100644
--- a/core/deco.c
+++ b/core/deco.c
@@ -482,7 +482,7 @@ void add_segment(struct deco_state *ds, double pressure, const struct gasmix *ga
 	(void) sac;
 	int ci;
 	struct gas_pressures pressures;
-
+	bool icd = false;
 	fill_pressures(&pressures, pressure - ((in_planner() && (decoMode() == VPMB)) ? WV_PRESSURE_SCHREINER : WV_PRESSURE),
 		       gasmix, (double) ccpo2 / 1000.0, dive->dc.divemode);
 
@@ -494,6 +494,11 @@ void add_segment(struct deco_state *ds, double pressure, const struct gasmix *ga
 		double n2_satmult = pn2_oversat > 0 ? buehlmann_config.satmult : buehlmann_config.desatmult;
 		double he_satmult = phe_oversat > 0 ? buehlmann_config.satmult : buehlmann_config.desatmult;
 
+		// Report ICD if N2 is more on-gasing than He off-gasing in leading tissue
+		if (ci == ds->ci_pointing_to_guiding_tissue && pn2_oversat > 0.0 && phe_oversat < 0.0 &&
+		    pn2_oversat * n2_satmult * n2_f + phe_oversat * he_satmult * he_f > 0)
+			icd = true;
+
 		ds->tissue_n2_sat[ci] += n2_satmult * pn2_oversat * n2_f;
 		ds->tissue_he_sat[ci] += he_satmult * phe_oversat * he_f;
 		ds->tissue_inertgas_saturation[ci] = ds->tissue_n2_sat[ci] + ds->tissue_he_sat[ci];
@@ -501,6 +506,7 @@ void add_segment(struct deco_state *ds, double pressure, const struct gasmix *ga
 	}
 	if (decoMode() == VPMB)
 		calc_crushing_pressure(ds, pressure);
+	ds->icd_warning = icd;
 	return;
 }
 
diff --git a/core/dive.h b/core/dive.h
index f81423f24..acbb6eb27 100644
--- a/core/dive.h
+++ b/core/dive.h
@@ -896,6 +896,7 @@ struct deco_state {
 	int ci_pointing_to_guiding_tissue;
 	double gf_low_pressure_this_dive;
 	int deco_time;
+	bool icd_warning;
 };
 
 extern void add_segment(struct deco_state *ds, double pressure, const struct gasmix *gasmix, int period_in_seconds, int setpoint, const struct dive *dive, int sac);
diff --git a/core/profile.c b/core/profile.c
index 2fbc3a892..835e68dcc 100644
--- a/core/profile.c
+++ b/core/profile.c
@@ -1036,7 +1036,8 @@ void calculate_deco_information(struct deco_state *ds, struct deco_state *planne
 			for (j = t0 + time_stepsize; j <= t1; j += time_stepsize) {
 				int depth = interpolate(entry[-1].depth, entry[0].depth, j - t0, t1 - t0);
 				add_segment(ds, depth_to_bar(depth, dive),
-					gasmix, time_stepsize, entry->o2pressure.mbar, dive, entry->sac);
+					    gasmix, time_stepsize, entry->o2pressure.mbar, dive, entry->sac);
+				entry->icd_warning = ds->icd_warning;
 				if ((t1 - j < time_stepsize) && (j < t1))
 					time_stepsize = t1 - j;
 			}
@@ -1498,6 +1499,8 @@ static void plot_string(struct plot_info *pi, struct plot_data *entry, struct me
 			}
 		}
 	}
+	if (entry->icd_warning)
+		put_format(b, "%s", translate("gettextFromC", "ICD in leading tissue\n"));
 	if (entry->heartbeat && prefs.hrgraph)
 		put_format_loc(b, translate("gettextFromC", "heart rate: %d\n"), entry->heartbeat);
 	if (entry->bearing >= 0)
diff --git a/core/profile.h b/core/profile.h
index fa92070c6..0a215d47e 100644
--- a/core/profile.h
+++ b/core/profile.h
@@ -63,6 +63,7 @@ struct plot_data {
 	double ambpressure;
 	double gfline;
 	double density;
+	bool icd_warning;
 };
 
 struct ev_select {