Consider previous dives when calculating deco

This also initializes the N2 tissue saturations to correct numbers
(setting them to zero was clearly silly).

With this commit we walk back in the dive_table until we find a surface
intervall that's longer than 48h. Or a dive that comes after the last one
we looked at; that would indicate that this is a divelist that contains
dives from multiple divers or dives that for other reasons are not
ordered. In a sane environment one would assume that the dives that need
to be taken into account when doing deco calculations are organized as one
trip in the XML file and so this logic should work.

One major downside of the current implementation is that we recalculate
everything whenever the plot_info is recreated - which happens quite
frequently, for example when resizing the window or even when we go into
loup mode. While this isn't all that compute intensive, this is an utter
waste and we should at least cache the saturation inherited from previous
dives (and clear that number when the selected dive changes). We don't
want to cache all of it as the recreation of the plot_info may be
triggered by the user changing equipment (and most importantly, gasmix)
information. In that case the deco data for this dive does indeed have to
be recreated. But without changing the current dive the saturation after
the last surface intervall should stay the same.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

1 files changed, 49 insertions, 14 deletions

diff --git a/deco.c b/deco.c
index 998d6637c..e18779ac8 100644
--- a/deco.c
+++ b/deco.c
@@ -7,10 +7,11 @@
  * The implementation below is (C) Dirk Hohndel 2012 and released under the GPLv2
  *
  * clear_deco()  - call to initialize for a new deco calculation
- * add_segment(pressure, gasmix) - add 1 second at the given pressure, breathing gasmix
+ * add_segment(pressure, gasmix, seconds) - add <seconds> at the given pressure, breathing gasmix
  * deco_allowed_depth(tissues_tolerance, surface_pressure, dive, smooth)
  *				- ceiling based on lead tissue, surface pressure, 3m increments or smooth
  */
+#include <math.h>
 #include "dive.h"
 
 //! Option structure for Buehlmann decompression.
@@ -76,6 +77,7 @@ const double buehlmann_He_factor_expositon_one_second[] = {
 	1.00198406028040E-004, 7.83611475491108E-005, 6.13689891868496E-005, 4.81280465299827E-005};
 
 #define WV_PRESSURE 0.0627 /* water vapor pressure */
+#define N2_IN_AIR 0.7902
 #define DIST_FROM_3_MTR 0.28
 #define PRESSURE_CHANGE_3M 0.3
 #define TOLERANCE 0.02
@@ -145,32 +147,65 @@ static double tissue_tolerance_calc(void)
 }
 
 /* add a second at the given pressure and gas to the deco calculation */
-double add_segment(double pressure, struct gasmix *gasmix)
+double add_segment(double pressure, struct gasmix *gasmix, int period_in_seconds)
 {
 	int ci;
 	double ppn2 = (pressure - WV_PRESSURE) * (1000 - gasmix->o2.permille - gasmix->he.permille) / 1000.0;
 	double pphe = (pressure - WV_PRESSURE) * gasmix->he.permille / 1000.0;
 
-	divetime++;
 	/* right now we just do OC */
-	for (ci = 0; ci < 16; ci++) {
-		if (ppn2 - tissue_n2_sat[ci] > 0)
-			tissue_n2_sat[ci] += buehlmann_config.satmult * (ppn2 - tissue_n2_sat[ci]) * buehlmann_N2_factor_expositon_one_second[ci];
-		else
-			tissue_n2_sat[ci] += buehlmann_config.desatmult * (ppn2 - tissue_n2_sat[ci]) * buehlmann_N2_factor_expositon_one_second[ci];
-		if (pphe - tissue_he_sat[ci] > 0)
-			tissue_he_sat[ci] += buehlmann_config.satmult * (pphe - tissue_he_sat[ci]) * buehlmann_He_factor_expositon_one_second[ci];
-		else
-			tissue_he_sat[ci] += buehlmann_config.desatmult * (pphe - tissue_he_sat[ci]) * buehlmann_He_factor_expositon_one_second[ci];
+	if (period_in_seconds == 1) { /* that's what we do during the dive */
+		for (ci = 0; ci < 16; ci++) {
+			if (ppn2 - tissue_n2_sat[ci] > 0)
+				tissue_n2_sat[ci] += buehlmann_config.satmult * (ppn2 - tissue_n2_sat[ci]) *
+								buehlmann_N2_factor_expositon_one_second[ci];
+			else
+				tissue_n2_sat[ci] += buehlmann_config.desatmult * (ppn2 - tissue_n2_sat[ci]) *
+								buehlmann_N2_factor_expositon_one_second[ci];
+			if (pphe - tissue_he_sat[ci] > 0)
+				tissue_he_sat[ci] += buehlmann_config.satmult * (pphe - tissue_he_sat[ci]) *
+								buehlmann_He_factor_expositon_one_second[ci];
+			else
+				tissue_he_sat[ci] += buehlmann_config.desatmult * (pphe - tissue_he_sat[ci]) *
+								buehlmann_He_factor_expositon_one_second[ci];
+		}
+	} else { /* all other durations */
+		for (ci = 0; ci < 16; ci++)
+		{
+			if (ppn2 - tissue_n2_sat[ci] > 0)
+				tissue_n2_sat[ci] += buehlmann_config.satmult * (ppn2 - tissue_n2_sat[ci]) *
+					(1 - pow(2.0,(- period_in_seconds / (buehlmann_N2_t_halflife[ci] * 60))));
+			else
+				tissue_n2_sat[ci] += buehlmann_config.desatmult * (ppn2 - tissue_n2_sat[ci]) *
+					(1 - pow(2.0,(- period_in_seconds / (buehlmann_N2_t_halflife[ci] * 60))));
+			if (pphe - tissue_he_sat[ci] > 0)
+				tissue_he_sat[ci] += buehlmann_config.satmult * (pphe - tissue_he_sat[ci]) *
+					(1 - pow(2.0,(- period_in_seconds / (buehlmann_He_t_halflife[ci] * 60))));
+			else
+				tissue_he_sat[ci] += buehlmann_config.desatmult * (pphe - tissue_he_sat[ci]) *
+					(1 - pow(2.0,(- period_in_seconds / (buehlmann_He_t_halflife[ci] * 60))));
+		}
 	}
 	return tissue_tolerance_calc();
 }
 
-void clear_deco()
+void dump_tissues()
+{
+	int ci;
+	printf("N2 tissues:");
+	for (ci = 0; ci < 16; ci++)
+		printf(" %6.3e", tissue_n2_sat[ci]);
+	printf("\nHe tissues:");
+	for (ci = 0; ci < 16; ci++)
+		printf(" %6.3e", tissue_he_sat[ci]);
+	printf("\n");
+}
+
+void clear_deco(double surface_pressure)
 {
 	int ci;
 	for (ci = 0; ci < 16; ci++) {
-		tissue_n2_sat[ci] = 0.0;
+		tissue_n2_sat[ci] = (surface_pressure - WV_PRESSURE) * N2_IN_AIR;
 		tissue_he_sat[ci] = 0.0;
 		tissue_tolerated_ambient_pressure[ci] = 0.0;
 	}