core: implement interpolate() function for unit types

Calls the global interpolate() function for integer types.

For now, the template is enabled if the arguments are not
integer types. Might want to refine that in the future.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/divelist.cpp

@@ -432,7 +432,7 @@ static void add_dive_to_deco(struct deco_state *ds, const struct dive &dive, boo
 		int j;
 
 		for (j = t0; j < t1; j++) {
-			depth_t depth = { .mm = interpolate(psample.depth.mm, sample.depth.mm, j - t0, t1 - t0) };
+			depth_t depth = interpolate(psample.depth, sample.depth, j - t0, t1 - t0);
 			auto gasmix = loop.at(j).first;
 			add_segment(ds, dive.depth_to_bar(depth), gasmix, 1, sample.setpoint.mbar,
 				    loop_d.at(j), dive.sac,

core/planner.cpp

@@ -104,7 +104,7 @@ static void interpolate_transition(struct deco_state *ds, struct dive *dive, dur
 	int32_t j;
 
 	for (j = t0.seconds; j < t1.seconds; j++) {
-		depth_t depth = depth_t { .mm = interpolate(d0.mm, d1.mm, j - t0.seconds, t1.seconds - t0.seconds) };
+		depth_t depth = interpolate(d0, d1, j - t0.seconds, t1.seconds - t0.seconds);
 		add_segment(ds, dive->depth_to_bar(depth), gasmix, 1, po2.mbar, divemode, prefs.bottomsac, true);
 	}
 	if (d1.mm > d0.mm)

core/profile.cpp

@@ -876,6 +876,7 @@ static void calculate_deco_information(struct deco_state *ds, const struct deco_
 			int time_stepsize = 20;
 			depth_t max_ceiling;
 			depth_t depth { .mm = entry.depth };
+			depth_t prev_depth { .mm = prev.depth };
 
 			divemode_t current_divemode = loop_d.at(entry.sec);
 			struct gasmix gasmix = loop.at(t1).first;
@@ -888,7 +889,7 @@ static void calculate_deco_information(struct deco_state *ds, const struct deco_
 			if (t0 != t1 && t1 - t0 < time_stepsize)
 				time_stepsize = t1 - t0;
 			for (int j = t0 + time_stepsize; j <= t1; j += time_stepsize) {
-				depth_t new_depth { .mm = interpolate(prev.depth, depth.mm, j - t0, t1 - t0) };
+				depth_t new_depth = interpolate(prev_depth, depth, j - t0, t1 - t0);
 				add_segment(ds, dive->depth_to_bar(new_depth),
 					    gasmix, time_stepsize, entry.o2pressure.mbar, current_divemode, entry.sac, in_planner);
 				entry.icd_warning = ds->icd_warning;
@@ -915,7 +916,7 @@ static void calculate_deco_information(struct deco_state *ds, const struct deco_
 				/* If using VPM-B, take first_ceiling_pressure as the deepest ceiling */
 				if (decoMode(in_planner) == VPMB) {
 					if  (current_ceiling.mm >= first_ceiling.mm ||
-					     (time_deep_ceiling == t0 && depth.mm == prev.depth)) {
+					     (time_deep_ceiling == t0 && depth.mm == prev_depth.mm)) {
 						time_deep_ceiling = t1;
 						first_ceiling = current_ceiling;
 						ds->first_ceiling_pressure.mbar = dive->depth_to_mbar(first_ceiling);

core/units.h

@@ -2,6 +2,8 @@
 #ifndef UNITS_H
 #define UNITS_H
 
+#include "interpolate.h"
+
 #include <math.h>
 #ifndef M_PI
 #define M_PI 3.14159265358979323846
@@ -86,6 +88,12 @@
  *	_permille	-> fraction_t in ‰
  *	_percent	-> fraction_t in %
  *
+ * For now, addition and subtraction of values of the same type
+ * are supported.
+ *
+ * A free standing interpolate() function can be used to interpolate
+ * between types of the same kind (see also the interpolate.h header).
+ *
  * We don't actually use these all yet, so maybe they'll change, but
  * I made a number of types as guidelines.
  */
@@ -140,6 +148,15 @@ struct unit_base {
 	}
 };
 
+template <typename T,
+	std::enable_if_t<!std::is_integral<T>::value, bool> = true>
+T interpolate(T a, T b, int part, int whole)
+{
+	return T::from_base(
+		interpolate(a.get_base(), b.get_base(), part, whole)
+	);
+}
+
 struct duration_t : public unit_base<duration_t>
 {
 	int32_t seconds = 0; // durations up to 34 yrs