From 1b593dc56c2c7545a1921fb896a0f32463cb1a06 Mon Sep 17 00:00:00 2001
From: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
Date: Tue, 25 Jun 2024 07:43:32 +0200
Subject: [PATCH] core: move cylinder related functions to struct dive

Seems natural in a C++ code base.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
---
 backend-shared/exportfuncs.cpp                |   2 +-
 commands/command_edit.cpp                     |   6 +-
 core/datatrak.cpp                             |  14 +-
 core/dive.cpp                                 | 177 +++++++++++++-----
 core/dive.h                                   |  20 +-
 core/divelist.cpp                             |  12 +-
 core/equipment.cpp                            |  23 +--
 core/equipment.h                              |   2 -
 core/gaspressures.cpp                         |  10 +-
 core/import-divinglog.cpp                     |   2 +-
 core/planner.cpp                              |  56 +++---
 core/plannernotes.cpp                         |   6 +-
 core/profile.cpp                              |  47 +----
 core/qthelper.cpp                             |   2 +-
 core/save-git.cpp                             |   2 +-
 core/save-xml.cpp                             |   2 +-
 core/statistics.cpp                           |  47 +----
 core/string-format.cpp                        |  10 +-
 desktop-widgets/simplewidgets.cpp             |   2 +-
 .../tab-widgets/TabDiveInformation.cpp        |   4 +-
 mobile-widgets/qmlmanager.cpp                 |  12 +-
 profile-widget/diveeventitem.cpp              |   4 +-
 profile-widget/diveprofileitem.cpp            |   6 +-
 profile-widget/profilescene.cpp               |   4 +-
 profile-widget/profilewidget2.cpp             |   6 +-
 profile-widget/tankitem.cpp                   |   4 +-
 qt-models/cylindermodel.cpp                   |  16 +-
 smtk-import/smartrak.cpp                      |   2 +-
 tests/testplan.cpp                            |   9 +-
 29 files changed, 250 insertions(+), 259 deletions(-)

diff --git a/backend-shared/exportfuncs.cpp b/backend-shared/exportfuncs.cpp
index eabc4a91b..6a6b8ee34 100644
--- a/backend-shared/exportfuncs.cpp
+++ b/backend-shared/exportfuncs.cpp
@@ -198,7 +198,7 @@ void export_TeX(const char *filename, bool selected_only, bool plain, ExportCall
 		put_format(&buf, "\n%% Gas use information:\n");
 		int qty_cyl = 0;
 		for (auto [i, cyl]: enumerated_range(dive->cylinders)) {
-			if (is_cylinder_used(dive.get(), i) || (prefs.include_unused_tanks && !cyl.type.description.empty())){
+			if (dive->is_cylinder_used(i) || (prefs.include_unused_tanks && !cyl.type.description.empty())){
 				put_format(&buf, "\\def\\%scyl%cdescription{%s}\n", ssrf, 'a' + i, cyl.type.description.c_str());
 				put_format(&buf, "\\def\\%scyl%cgasname{%s}\n", ssrf, 'a' + i, gasname(cyl.gasmix));
 				put_format(&buf, "\\def\\%scyl%cmixO2{%.1f\\%%}\n", ssrf, 'a' + i, get_o2(cyl.gasmix)/10.0);
diff --git a/commands/command_edit.cpp b/commands/command_edit.cpp
index 6276896c0..0816ffb30 100644
--- a/commands/command_edit.cpp
+++ b/commands/command_edit.cpp
@@ -1146,7 +1146,7 @@ EditCylinderBase::EditCylinderBase(int index, bool currentDiveOnly, bool nonProt
 		dives.clear();
 		return;
 	}
-	const cylinder_t &orig = *get_cylinder(current, index);
+	const cylinder_t &orig = *current->get_cylinder(index);
 
 	std::vector<dive *> divesNew;
 	divesNew.reserve(dives.size());
@@ -1156,7 +1156,7 @@ EditCylinderBase::EditCylinderBase(int index, bool currentDiveOnly, bool nonProt
 	for (dive *d: dives) {
 		if (index >= static_cast<int>(d->cylinders.size()))
 			continue;
-		if (nonProtectedOnly && is_cylinder_prot(d, index))
+		if (nonProtectedOnly && d->is_cylinder_prot(index))
 			continue;
 		// We checked that the cylinder exists above.
 		const cylinder_t &cylinder = d->cylinders[index];
@@ -1272,7 +1272,7 @@ void EditCylinder::redo()
 	for (size_t i = 0; i < dives.size(); ++i) {
 		const std::string &name = cyl[i].type.description;
 		set_tank_info_data(tank_info_table, name, cyl[i].type.size, cyl[i].type.workingpressure);
-		std::swap(*get_cylinder(dives[i], indexes[i]), cyl[i]);
+		std::swap(*dives[i]->get_cylinder(indexes[i]), cyl[i]);
 		divelog.dives.update_cylinder_related_info(*dives[i]);
 		emit diveListNotifier.cylinderEdited(dives[i], indexes[i]);
 		invalidate_dive_cache(dives[i]); // Ensure that dive is written in git_save()
diff --git a/core/datatrak.cpp b/core/datatrak.cpp
index a343599fe..6a8c2bb35 100644
--- a/core/datatrak.cpp
+++ b/core/datatrak.cpp
@@ -372,7 +372,7 @@ static char *dt_dive_parser(unsigned char *runner, struct dive *dt_dive, struct
 	 */
 	read_bytes(2);
 	if (tmp_2bytes != 0x7FFF && dt_dive->cylinders.size() > 0)
-		get_cylinder(dt_dive, 0)->gas_used.mliter = lrint(get_cylinder(dt_dive, 0)->type.size.mliter * (tmp_2bytes / 100.0));
+		dt_dive->get_cylinder(0)->gas_used.mliter = lrint(dt_dive->get_cylinder(0)->type.size.mliter * (tmp_2bytes / 100.0));
 
 	/*
 	 * Dive Type 1 -  Bit table. Subsurface don't have this record, but
@@ -544,10 +544,10 @@ static char *dt_dive_parser(unsigned char *runner, struct dive *dt_dive, struct
 			goto bail;
 		}
 		if (is_nitrox && dt_dive->cylinders.size() > 0)
-			get_cylinder(dt_dive, 0)->gasmix.o2.permille =
+			dt_dive->get_cylinder(0)->gasmix.o2.permille =
 					lrint(membuf[23] & 0x0F ? 20.0 + 2 * (membuf[23] & 0x0F) : 21.0) * 10;
 		if (is_O2 && dt_dive->cylinders.size() > 0)
-			get_cylinder(dt_dive, 0)->gasmix.o2.permille = membuf[23] * 10;
+			dt_dive->get_cylinder(0)->gasmix.o2.permille = membuf[23] * 10;
 		free(compl_buffer);
 	}
 	JUMP(membuf, profile_length);
@@ -560,8 +560,8 @@ static char *dt_dive_parser(unsigned char *runner, struct dive *dt_dive, struct
 	else
 		dt_dive->dcs[0].deviceid = 0xffffffff;
 	if (!is_SCR && dt_dive->cylinders.size() > 0) {
-		get_cylinder(dt_dive, 0)->end.mbar = get_cylinder(dt_dive, 0)->start.mbar -
-			((get_cylinder(dt_dive, 0)->gas_used.mliter / get_cylinder(dt_dive, 0)->type.size.mliter) * 1000);
+		dt_dive->get_cylinder(0)->end.mbar = dt_dive->get_cylinder(0)->start.mbar -
+			((dt_dive->get_cylinder(0)->gas_used.mliter / dt_dive->get_cylinder(0)->type.size.mliter) * 1000);
 	}
 	return (char *)membuf;
 bail:
@@ -638,8 +638,8 @@ static void wlog_compl_parser(std::string &wl_mem, struct dive *dt_dive, int dco
 	 */
 	tmp = (int) two_bytes_to_int(runner[pos_tank_init + 1], runner[pos_tank_init]);
 	if (tmp != 0x7fff) {
-		get_cylinder(dt_dive, 0)->start.mbar = tmp * 10;
-		get_cylinder(dt_dive, 0)->end.mbar =  get_cylinder(dt_dive, 0)->start.mbar - lrint(get_cylinder(dt_dive, 0)->gas_used.mliter / get_cylinder(dt_dive, 0)->type.size.mliter) * 1000;
+		dt_dive->get_cylinder(0)->start.mbar = tmp * 10;
+		dt_dive->get_cylinder(0)->end.mbar =  dt_dive->get_cylinder(0)->start.mbar - lrint(dt_dive->get_cylinder(0)->gas_used.mliter / dt_dive->get_cylinder(0)->type.size.mliter) * 1000;
 	}
 
 	/*
diff --git a/core/dive.cpp b/core/dive.cpp
index 5cad9f867..a49fed566 100644
--- a/core/dive.cpp
+++ b/core/dive.cpp
@@ -14,6 +14,7 @@
 #include "divelist.h"
 #include "divelog.h"
 #include "divesite.h"
+#include "equipment.h"
 #include "errorhelper.h"
 #include "event.h"
 #include "extradata.h"
@@ -51,6 +52,19 @@ dive::dive(dive &&) = default;
 dive &dive::operator=(const dive &) = default;
 dive::~dive() = default;
 
+/* get_cylinder_idx_by_use(): Find the index of the first cylinder with a particular CCR use type.
+ * The index returned corresponds to that of the first cylinder with a cylinder_use that
+ * equals the appropriate enum value [oxygen, diluent, bailout] given by cylinder_use_type.
+ * A negative number returned indicates that a match could not be found.
+ * Call parameters: dive = the dive being processed
+ *                  cylinder_use_type = an enum, one of {oxygen, diluent, bailout} */
+static int get_cylinder_idx_by_use(const struct dive &dive, enum cylinderuse cylinder_use_type)
+{
+	auto it = std::find_if(dive.cylinders.begin(), dive.cylinders.end(), [cylinder_use_type]
+			       (auto &cyl) { return cyl.cylinder_use == cylinder_use_type; });
+	return it != dive.cylinders.end() ? it - dive.cylinders.begin() : -1;
+}
+
 /*
  * The legacy format for sample pressures has a single pressure
  * for each sample that can have any sensor, plus a possible
@@ -66,7 +80,7 @@ int legacy_format_o2pressures(const struct dive *dive, const struct divecomputer
 {
 	int o2sensor;
 
-	o2sensor = (dc->divemode == CCR) ? get_cylinder_idx_by_use(dive, OXYGEN) : -1;
+	o2sensor = (dc->divemode == CCR) ? get_cylinder_idx_by_use(*dive, OXYGEN) : -1;
 	for (const auto &s: dc->samples) {
 		int seen_pressure = 0, idx;
 
@@ -92,11 +106,30 @@ int legacy_format_o2pressures(const struct dive *dive, const struct divecomputer
 	return o2sensor < 0 ? 256 : o2sensor;
 }
 
+/* access to cylinders is controlled by two functions:
+ * - get_cylinder() returns the cylinder of a dive and supposes that
+ *   the cylinder with the given index exists. If it doesn't, an error
+ *   message is printed and the "surface air" cylinder returned.
+ *   (NOTE: this MUST not be written into!).
+ * - get_or_create_cylinder() creates an empty cylinder if it doesn't exist.
+ *   Multiple cylinders might be created if the index is bigger than the
+ *   number of existing cylinders
+ */
+cylinder_t *dive::get_cylinder(int idx)
+{
+	return &cylinders[idx];
+}
+
+const cylinder_t *dive::get_cylinder(int idx) const
+{
+	return &cylinders[idx];
+}
+
 /* warning: does not test idx for validity */
 struct event create_gas_switch_event(struct dive *dive, struct divecomputer *dc, int seconds, int idx)
 {
 	/* The gas switch event format is insane for historical reasons */
-	struct gasmix mix = get_cylinder(dive, idx)->gasmix;
+	struct gasmix mix = dive->get_cylinder(idx)->gasmix;
 	int o2 = get_o2(mix);
 	int he = get_he(mix);
 
@@ -124,13 +157,13 @@ void add_gas_switch_event(struct dive *dive, struct divecomputer *dc, int second
 	add_event_to_dc(dc, std::move(ev));
 }
 
-struct gasmix get_gasmix_from_event(const struct dive *dive, const struct event &ev)
+struct gasmix dive::get_gasmix_from_event(const struct event &ev) const
 {
 	if (ev.is_gaschange()) {
 		int index = ev.gas.index;
 		// FIXME: The planner uses one past cylinder-count to signify "surface air". Remove in due course.
-		if (index >= 0 && static_cast<size_t>(index) < dive->cylinders.size() + 1)
-			return get_cylinder(dive, index)->gasmix;
+		if (index >= 0 && static_cast<size_t>(index) < cylinders.size() + 1)
+			return get_cylinder(index)->gasmix;
 		return ev.gas.mix;
 	}
 	return gasmix_air;
@@ -240,7 +273,7 @@ void copy_used_cylinders(const struct dive *s, struct dive *d, bool used_only)
 
 	d->cylinders.clear();
 	for (auto [i, cyl]: enumerated_range(s->cylinders)) {
-		if (!used_only || is_cylinder_used(s, i) || get_cylinder(s, i)->cylinder_use == NOT_USED)
+		if (!used_only || s->is_cylinder_used(i) || s->get_cylinder(i)->cylinder_use == NOT_USED)
 			d->cylinders.push_back(cyl);
 	}
 }
@@ -308,13 +341,39 @@ static int get_cylinder_used(const struct dive *dive, bool used[])
 	return num;
 }
 
+/*
+ * If the event has an explicit cylinder index,
+ * we return that. If it doesn't, we return the best
+ * match based on the gasmix.
+ *
+ * Some dive computers give cylinder indices, some
+ * give just the gas mix.
+ */
+int dive::get_cylinder_index(const struct event &ev) const
+{
+	if (ev.gas.index >= 0)
+		return ev.gas.index;
+
+	/*
+	 * This should no longer happen!
+	 *
+	 * We now match up gas change events with their cylinders at dive
+	 * event fixup time.
+	 */
+	report_info("Still looking up cylinder based on gas mix in get_cylinder_index()!");
+
+	gasmix mix = get_gasmix_from_event(ev);
+	int best = find_best_gasmix_match(mix, cylinders);
+	return best < 0 ? 0 : best;
+}
+
 /* Are there any used cylinders which we do not know usage about? */
-static bool has_unknown_used_cylinders(const struct dive *dive, const struct divecomputer *dc,
+static bool has_unknown_used_cylinders(const struct dive &dive, const struct divecomputer *dc,
 				       const bool used_cylinders[], int num)
 {
 	int idx;
-	auto used_and_unknown = std::make_unique<bool[]>(dive->cylinders.size());
-	std::copy(used_cylinders, used_cylinders + dive->cylinders.size(), used_and_unknown.get());
+	auto used_and_unknown = std::make_unique<bool[]>(dive.cylinders.size());
+	std::copy(used_cylinders, used_cylinders + dive.cylinders.size(), used_and_unknown.get());
 
 	/* We know about using the O2 cylinder in a CCR dive */
 	if (dc->divemode == CCR) {
@@ -326,7 +385,7 @@ static bool has_unknown_used_cylinders(const struct dive *dive, const struct div
 	}
 
 	/* We know about the explicit first cylinder (or first) */
-	idx = explicit_first_cylinder(dive, dc);
+	idx = dive.explicit_first_cylinder(dc);
 	if (idx >= 0 && used_and_unknown[idx]) {
 		used_and_unknown[idx] = false;
 		num--;
@@ -336,7 +395,7 @@ static bool has_unknown_used_cylinders(const struct dive *dive, const struct div
 	event_loop loop("gaschange");
 	const struct event *ev;
 	while ((ev = loop.next(*dc)) != nullptr && num > 0) {
-		idx = get_cylinder_index(dive, *ev);
+		idx = dive.get_cylinder_index(*ev);
 		if (idx >= 0 && used_and_unknown[idx]) {
 			used_and_unknown[idx] = false;
 			num--;
@@ -368,7 +427,7 @@ void per_cylinder_mean_depth(const struct dive *dive, struct divecomputer *dc, i
 	 */
 	auto used_cylinders = std::make_unique<bool[]>(dive->cylinders.size());
 	num_used_cylinders = get_cylinder_used(dive, used_cylinders.get());
-	if (has_unknown_used_cylinders(dive, dc, used_cylinders.get(), num_used_cylinders)) {
+	if (has_unknown_used_cylinders(*dive, dc, used_cylinders.get(), num_used_cylinders)) {
 		/*
 		 * If we had more than one used cylinder, but
 		 * do not know usage of them, we simply cannot
@@ -401,7 +460,7 @@ void per_cylinder_mean_depth(const struct dive *dive, struct divecomputer *dc, i
 
 		/* Make sure to move the event past 'lasttime' */
 		while (ev && lasttime >= ev->time.seconds) {
-			idx = get_cylinder_index(dive, *ev);
+			idx = dive->get_cylinder_index(*ev);
 			ev = loop.next(*dc);
 		}
 
@@ -454,19 +513,19 @@ static int same_rounded_pressure(pressure_t a, pressure_t b)
  * first cylinder - in which case cylinder 0 is indeed the first cylinder.
  * We likewise return 0 if the event concerns a cylinder that doesn't exist.
  * If the dive has no cylinders, -1 is returned. */
-int explicit_first_cylinder(const struct dive *dive, const struct divecomputer *dc)
+int dive::explicit_first_cylinder(const struct divecomputer *dc) const
 {
 	int res = 0;
-	if (dive->cylinders.empty())
+	if (cylinders.empty())
 		return -1;
 	if (dc) {
 		const struct event *ev = get_first_event(*dc, "gaschange");
 		if (ev && ((!dc->samples.empty() && ev->time.seconds == dc->samples[0].time.seconds) || ev->time.seconds <= 1))
-			res = get_cylinder_index(dive, *ev);
+			res = get_cylinder_index(*ev);
 		else if (dc->divemode == CCR)
-			res = std::max(get_cylinder_idx_by_use(dive, DILUENT), res);
+			res = std::max(get_cylinder_idx_by_use(*this, DILUENT), res);
 	}
-	return static_cast<size_t>(res) < dive->cylinders.size() ? res : 0;
+	return static_cast<size_t>(res) < cylinders.size() ? res : 0;
 }
 
 static double calculate_depth_to_mbarf(int depth, pressure_t surface_pressure, int salinity);
@@ -492,13 +551,13 @@ void update_setpoint_events(const struct dive *dive, struct divecomputer *dc)
 		// pO2 values we would have computed anyway.
 		event_loop loop("gaschange");
 		const struct event *ev = loop.next(*dc);
-		struct gasmix gasmix = get_gasmix_from_event(dive, *ev);
+		struct gasmix gasmix = dive->get_gasmix_from_event(*ev);
 		const struct event *next = loop.next(*dc);
 
 		for (auto &sample: dc->samples) {
 			if (next && sample.time.seconds >= next->time.seconds) {
 				ev = next;
-				gasmix = get_gasmix_from_event(dive, *ev);
+				gasmix = dive->get_gasmix_from_event(*ev);
 				next = loop.next(*dc);
 			}
 			gas_pressures pressures = fill_pressures(lrint(calculate_depth_to_mbarf(sample.depth.mm, dc->surface_pressure, 0)), gasmix ,0, dc->divemode);
@@ -1367,19 +1426,6 @@ pick_b:
 		add_initial_gaschange(d, res, offset, cylinders_map2[0]);
 }
 
-/* get_cylinder_idx_by_use(): Find the index of the first cylinder with a particular CCR use type.
- * The index returned corresponds to that of the first cylinder with a cylinder_use that
- * equals the appropriate enum value [oxygen, diluent, bailout] given by cylinder_use_type.
- * A negative number returned indicates that a match could not be found.
- * Call parameters: dive = the dive being processed
- *                  cylinder_use_type = an enum, one of {oxygen, diluent, bailout} */
-int get_cylinder_idx_by_use(const struct dive *dive, enum cylinderuse cylinder_use_type)
-{
-	auto it = std::find_if(dive->cylinders.begin(), dive->cylinders.end(), [cylinder_use_type]
-			       (auto &cyl) { return cyl.cylinder_use == cylinder_use_type; });
-	return it != dive->cylinders.end() ? it - dive->cylinders.begin() : -1;
-}
-
 /* Force an initial gaschange event to the (old) gas #0 */
 static void add_initial_gaschange(struct dive &dive, struct divecomputer &dc, int offset, int idx)
 {
@@ -1472,7 +1518,7 @@ int same_gasmix_cylinder(const cylinder_t &cyl, int cylid, const struct dive *di
 		if (i == cylid)
 			continue;
 		struct gasmix gas2 = cyl.gasmix;
-		if (gasmix_distance(mygas, gas2) == 0 && (is_cylinder_used(dive, i) || check_unused))
+		if (gasmix_distance(mygas, gas2) == 0 && (dive->is_cylinder_used(i) || check_unused))
 			return i;
 	}
 	return -1;
@@ -1598,7 +1644,7 @@ static bool cylinder_in_use(const struct dive *dive, int idx)
 		return false;
 
 	/* This tests for gaschange events or pressure changes */
-	if (is_cylinder_used(dive, idx) || prefs.include_unused_tanks)
+	if (dive->is_cylinder_used(idx) || prefs.include_unused_tanks)
 		return true;
 
 	/* This tests for typenames or gas contents */
@@ -1660,7 +1706,7 @@ static void merge_cylinders(struct dive &res, const struct dive &a, const struct
 		if (!used_in_b[i])
 			continue;
 
-		j = match_cylinder(get_cylinder(&b, i), res, try_to_match.get());
+		j = match_cylinder(b.get_cylinder(i), res, try_to_match.get());
 
 		/* No match? Add it to the result */
 		if (j < 0) {
@@ -1672,7 +1718,7 @@ static void merge_cylinders(struct dive &res, const struct dive &a, const struct
 
 		/* Otherwise, merge the result to the one we found */
 		mapping_b[i] = j;
-		merge_one_cylinder(get_cylinder(&res, j), get_cylinder(&b, i));
+		merge_one_cylinder(res.get_cylinder(j), b.get_cylinder(i));
 
 		/* Don't match the same target more than once */
 		try_to_match[j] = false;
@@ -2589,8 +2635,8 @@ gasmix_loop::gasmix_loop(const struct dive &d, const struct divecomputer &dc) :
 		return;
 
 	/* on first invocation, get initial gas mix and first event (if any) */
-	int cyl = explicit_first_cylinder(&dive, &dc);
-	last = get_cylinder(&dive, cyl)->gasmix;
+	int cyl = dive.explicit_first_cylinder(&dc);
+	last = dive.get_cylinder(cyl)->gasmix;
 	ev = loop.next(dc);
 }
 
@@ -2601,7 +2647,7 @@ gasmix gasmix_loop::next(int time)
 		return last;
 
 	while (ev && ev->time.seconds <= time) {
-		last = get_gasmix_from_event(&dive, *ev);
+		last = dive.get_gasmix_from_event(*ev);
 		ev = loop.next(dc);
 	}
 	return last;
@@ -2609,9 +2655,9 @@ gasmix gasmix_loop::next(int time)
 
 /* get the gas at a certain time during the dive */
 /* If there is a gasswitch at that time, it returns the new gasmix */
-struct gasmix get_gasmix_at_time(const struct dive &d, const struct divecomputer &dc, duration_t time)
+struct gasmix dive::get_gasmix_at_time(const struct divecomputer &dc, duration_t time) const
 {
-	return gasmix_loop(d, dc).next(time.seconds);
+	return gasmix_loop(*this, dc).next(time.seconds);
 }
 
 /* Does that cylinder have any pressure readings? */
@@ -2682,7 +2728,7 @@ dive::get_maximal_gas_result dive::get_maximal_gas() const
 		int o2 = get_o2(cyl.gasmix);
 		int he = get_he(cyl.gasmix);
 
-		if (!is_cylinder_used(this, i))
+		if (!is_cylinder_used(i))
 			continue;
 		if (cyl.cylinder_use == OXYGEN)
 			continue;
@@ -2703,3 +2749,48 @@ dive::get_maximal_gas_result dive::get_maximal_gas() const
 		maxo2 = mino2 = 0;
 	return { mino2, maxhe, maxo2 };
 }
+
+bool dive::has_gaschange_event(const struct divecomputer *dc, int idx) const
+{
+	bool first_gas_explicit = false;
+	event_loop loop("gaschange");
+	while (auto event = loop.next(*dc)) {
+		if (!dc->samples.empty() && (event->time.seconds == 0 ||
+				   (dc->samples[0].time.seconds == event->time.seconds)))
+			first_gas_explicit = true;
+		if (get_cylinder_index(*event) == idx)
+			return true;
+	}
+	return !first_gas_explicit && idx == 0;
+}
+
+bool dive::is_cylinder_used(int idx) const
+{
+	if (idx < 0 || static_cast<size_t>(idx) >= cylinders.size())
+		return false;
+
+	const cylinder_t &cyl = cylinders[idx];
+	if ((cyl.start.mbar - cyl.end.mbar) > SOME_GAS)
+		return true;
+
+	if ((cyl.sample_start.mbar - cyl.sample_end.mbar) > SOME_GAS)
+		return true;
+
+	for (auto &dc: dcs) {
+		if (has_gaschange_event(&dc, idx))
+			return true;
+		else if (dc.divemode == CCR && idx == get_cylinder_idx_by_use(*this, OXYGEN))
+			return true;
+	}
+	return false;
+}
+
+bool dive::is_cylinder_prot(int idx) const
+{
+	if (idx < 0 || static_cast<size_t>(idx) >= cylinders.size())
+		return false;
+
+	return std::any_of(dcs.begin(), dcs.end(),
+			   [this, idx](auto &dc)
+			   { return has_gaschange_event(&dc, idx); });
+}
diff --git a/core/dive.h b/core/dive.h
index 0ea75d4c6..75adb9256 100644
--- a/core/dive.h
+++ b/core/dive.h
@@ -91,6 +91,15 @@ struct dive {
 	bool is_planned() const;
 	bool is_logged() const;
 	bool likely_same(const struct dive &b) const;
+	bool is_cylinder_used(int idx) const;
+	bool is_cylinder_prot(int idx) const;
+	int explicit_first_cylinder(const struct divecomputer *dc) const;
+	int get_cylinder_index(const struct event &ev) const;
+	bool has_gaschange_event(const struct divecomputer *dc, int idx) const;
+	struct gasmix get_gasmix_from_event(const struct event &ev) const;
+	struct gasmix get_gasmix_at_time(const struct divecomputer &dc, duration_t time) const;
+	cylinder_t *get_cylinder(int idx);
+	const cylinder_t *get_cylinder(int idx) const;
 
 	int depth_to_mbar(int depth) const;
 	double depth_to_mbarf(int depth) const;
@@ -115,7 +124,6 @@ struct dive_or_trip {
 extern void invalidate_dive_cache(struct dive *dive);
 extern bool dive_cache_is_valid(const struct dive *dive);
 
-extern int get_cylinder_idx_by_use(const struct dive *dive, enum cylinderuse cylinder_use_type);
 extern void cylinder_renumber(struct dive &dive, int mapping[]);
 extern int same_gasmix_cylinder(const cylinder_t &cyl, int cylid, const struct dive *dive, bool check_unused);
 
@@ -139,9 +147,6 @@ struct dive_components {
 	unsigned int when : 1;
 };
 
-extern bool has_gaschange_event(const struct dive *dive, const struct divecomputer *dc, int idx);
-extern int explicit_first_cylinder(const struct dive *dive, const struct divecomputer *dc);
-
 extern fraction_t best_o2(depth_t depth, const struct dive *dive, bool in_planner);
 extern fraction_t best_he(depth_t depth, const struct dive *dive, bool o2narcotic, fraction_t fo2);
 
@@ -193,13 +198,9 @@ extern int dive_getUniqID();
 
 extern void copy_events_until(const struct dive *sd, struct dive *dd, int dcNr, int time);
 extern void copy_used_cylinders(const struct dive *s, struct dive *d, bool used_only);
-extern bool is_cylinder_used(const struct dive *dive, int idx);
-extern bool is_cylinder_prot(const struct dive *dive, int idx);
 extern void add_gas_switch_event(struct dive *dive, struct divecomputer *dc, int time, int idx);
 extern struct event create_gas_switch_event(struct dive *dive, struct divecomputer *dc, int seconds, int idx);
 extern void per_cylinder_mean_depth(const struct dive *dive, struct divecomputer *dc, int *mean, int *duration);
-extern int get_cylinder_index(const struct dive *dive, const struct event &ev);
-extern struct gasmix get_gasmix_from_event(const struct dive *, const struct event &ev);
 extern bool cylinder_with_sensor_sample(const struct dive *dive, int cylinder_id);
 
 /* UI related protopypes */
@@ -208,9 +209,6 @@ extern void invalidate_dive_cache(struct dive *dc);
 
 extern int total_weight(const struct dive *);
 
-/* Get gasmix at a given time */
-extern struct gasmix get_gasmix_at_time(const struct dive &dive, const struct divecomputer &dc, duration_t time);
-
 extern void update_setpoint_events(const struct dive *dive, struct divecomputer *dc);
 
 /* Make pointers to dive and dive_trip "Qt metatypes" so that they can be passed through
diff --git a/core/divelist.cpp b/core/divelist.cpp
index 28152847f..6abc4c916 100644
--- a/core/divelist.cpp
+++ b/core/divelist.cpp
@@ -117,7 +117,7 @@ int total_weight(const struct dive *dive)
 
 static int active_o2(const struct dive &dive, const struct divecomputer *dc, duration_t time)
 {
-	struct gasmix gas = get_gasmix_at_time(dive, *dc, time);
+	struct gasmix gas = dive.get_gasmix_at_time(*dc, time);
 	return get_o2(gas);
 }
 
@@ -137,8 +137,8 @@ static int get_sample_o2(const struct dive &dive, const struct divecomputer *dc,
 		double amb_presure = dive.depth_to_bar(sample.depth.mm);
 		double pamb_pressure = dive.depth_to_bar(psample.depth.mm );
 		if (dc->divemode == PSCR) {
-			po2i = pscr_o2(pamb_pressure, get_gasmix_at_time(dive, *dc, psample.time));
-			po2f = pscr_o2(amb_presure, get_gasmix_at_time(dive, *dc, sample.time));
+			po2i = pscr_o2(pamb_pressure, dive.get_gasmix_at_time(*dc, psample.time));
+			po2f = pscr_o2(amb_presure, dive.get_gasmix_at_time(*dc, sample.time));
 		} else {
 			int o2 = active_o2(dive, dc, psample.time);	// 	... calculate po2 from depth and FiO2.
 			po2i = lrint(o2 * pamb_pressure);	// (initial) po2 at start of segment
@@ -182,8 +182,8 @@ static int calculate_otu(const struct dive &dive)
 				double amb_presure = dive.depth_to_bar(sample.depth.mm);
 				double pamb_pressure = dive.depth_to_bar(psample.depth.mm);
 				if (dc->divemode == PSCR) {
-					po2i = pscr_o2(pamb_pressure, get_gasmix_at_time(dive, *dc, psample.time));
-					po2f = pscr_o2(amb_presure, get_gasmix_at_time(dive, *dc, sample.time));
+					po2i = pscr_o2(pamb_pressure, dive.get_gasmix_at_time(*dc, psample.time));
+					po2f = pscr_o2(amb_presure, dive.get_gasmix_at_time(*dc, sample.time));
 				} else {
 					int o2 = active_o2(dive, dc, psample.time);	// 	... calculate po2 from depth and FiO2.
 					po2i = lrint(o2 * pamb_pressure);	// (initial) po2 at start of segment
@@ -388,7 +388,7 @@ static double calculate_airuse(const struct dive &dive)
 			// better not pretend we know the total gas use.
 			// Eventually, logic should be fixed to compute average depth and total time
 			// for those segments where cylinders with known pressure drop are breathed from.
-			if (is_cylinder_used(&dive, i))
+			if (dive.is_cylinder_used(i))
 				return 0.0;
 			else
 				continue;
diff --git a/core/equipment.cpp b/core/equipment.cpp
index 800a786a0..49e08caa7 100644
--- a/core/equipment.cpp
+++ b/core/equipment.cpp
@@ -369,25 +369,6 @@ cylinder_t *add_empty_cylinder(struct cylinder_table *t)
 	return &t->back();
 }
 
-/* access to cylinders is controlled by two functions:
- * - get_cylinder() returns the cylinder of a dive and supposes that
- *   the cylinder with the given index exists. If it doesn't, an error
- *   message is printed and the "surface air" cylinder returned.
- *   (NOTE: this MUST not be written into!).
- * - get_or_create_cylinder() creates an empty cylinder if it doesn't exist.
- *   Multiple cylinders might be created if the index is bigger than the
- *   number of existing cylinders
- */
-cylinder_t *get_cylinder(struct dive *d, int idx)
-{
-	return &d->cylinders[idx];
-}
-
-const cylinder_t *get_cylinder(const struct dive *d, int idx)
-{
-	return &d->cylinders[idx];
-}
-
 cylinder_t *get_or_create_cylinder(struct dive *d, int idx)
 {
 	if (idx < 0) {
@@ -468,7 +449,7 @@ void add_default_cylinder(struct dive *d)
 
 static bool show_cylinder(const struct dive *d, int i)
 {
-	if (is_cylinder_used(d, i))
+	if (d->is_cylinder_used(i))
 		return true;
 
 	const cylinder_t &cyl = d->cylinders[i];
@@ -499,7 +480,7 @@ void dump_cylinders(struct dive *dive, bool verbose)
 {
 	printf("Cylinder list:\n");
 	for (int i = 0; i < dive->cylinders; i++) {
-		cylinder_t *cyl = get_cylinder(dive, i);
+		cylinder_t *cyl = dive->get_cylinder(i);
 
 		printf("%02d: Type     %s, %3.1fl, %3.0fbar\n", i, cyl->type.description.c_str(), cyl->type.size.mliter / 1000.0, cyl->type.workingpressure.mbar / 1000.0);
 		printf("    Gasmix   O2 %2.0f%% He %2.0f%%\n", cyl->gasmix.o2.permille / 10.0, cyl->gasmix.he.permille / 10.0);
diff --git a/core/equipment.h b/core/equipment.h
index c64bfd8d0..08143a4d3 100644
--- a/core/equipment.h
+++ b/core/equipment.h
@@ -71,8 +71,6 @@ using weightsystem_table = std::vector<weightsystem_t>;
 extern enum cylinderuse cylinderuse_from_text(const char *text);
 extern void copy_cylinder_types(const struct dive *s, struct dive *d);
 extern cylinder_t *add_empty_cylinder(struct cylinder_table *t);
-extern cylinder_t *get_cylinder(struct dive *d, int idx);
-extern const cylinder_t *get_cylinder(const struct dive *d, int idx);
 extern cylinder_t *get_or_create_cylinder(struct dive *d, int idx);
 extern bool same_weightsystem(weightsystem_t w1, weightsystem_t w2);
 extern void remove_cylinder(struct dive *dive, int idx);
diff --git a/core/gaspressures.cpp b/core/gaspressures.cpp
index 1c6b3b6bc..0034c42e2 100644
--- a/core/gaspressures.cpp
+++ b/core/gaspressures.cpp
@@ -187,7 +187,7 @@ static void fill_missing_tank_pressures(const struct dive *dive, struct plot_inf
 	if (track_pr.empty())
 		return;
 
-	if (get_cylinder(dive, cyl)->cylinder_use == OC_GAS)
+	if (dive->get_cylinder(cyl)->cylinder_use == OC_GAS)
 		strategy = SAC;
 	else
 		strategy = TIME;
@@ -248,7 +248,7 @@ static void fill_missing_tank_pressures(const struct dive *dive, struct plot_inf
 			last_segment = it;
 		}
 
-		if(get_cylinder(dive, cyl)->cylinder_use == OC_GAS) {
+		if(dive->get_cylinder(cyl)->cylinder_use == OC_GAS) {
 
 			/* if this segment has pressure_time, then calculate a new interpolated pressure */
 			if (interpolate.pressure_time) {
@@ -310,7 +310,7 @@ static void debug_print_pressures(struct plot_info &pi)
 void populate_pressure_information(const struct dive *dive, const struct divecomputer *dc, struct plot_info &pi, int sensor)
 {
 	int first, last, cyl;
-	const cylinder_t *cylinder = get_cylinder(dive, sensor);
+	const cylinder_t *cylinder = dive->get_cylinder(sensor);
 	std::vector<pr_track_t> track;
 	size_t current = std::string::npos;
 	int missing_pr = 0, dense = 1;
@@ -350,7 +350,7 @@ void populate_pressure_information(const struct dive *dive, const struct divecom
 	 */
 	cyl = sensor;
 	event_loop loop_gas("gaschange");
-	const struct event *ev = has_gaschange_event(dive, dc, sensor) ?
+	const struct event *ev = dive->has_gaschange_event(dc, sensor) ?
 		loop_gas.next(*dc) : nullptr;
 	divemode_loop loop_mode(*dc);
 
@@ -360,7 +360,7 @@ void populate_pressure_information(const struct dive *dive, const struct divecom
 		int time = entry.sec;
 
 		while (ev && ev->time.seconds <= time) {   // Find 1st gaschange event after 
-			cyl = get_cylinder_index(dive, *ev); // the current gas change.
+			cyl = dive->get_cylinder_index(*ev); // the current gas change.
 			if (cyl < 0)
 				cyl = sensor;
 			ev = loop_gas.next(*dc);
diff --git a/core/import-divinglog.cpp b/core/import-divinglog.cpp
index 32df725fc..8b5ea1065 100644
--- a/core/import-divinglog.cpp
+++ b/core/import-divinglog.cpp
@@ -140,7 +140,7 @@ static int divinglog_profile(void *param, int, char **data, char **)
 			state->cur_sample->pressure[0].mbar = pressure * 100;
 			state->cur_sample->rbt.seconds = rbt;
 			if (oldcyl != tank && tank >= 0 && static_cast<size_t>(tank) < state->cur_dive->cylinders.size()) {
-				struct gasmix mix = get_cylinder(state->cur_dive.get(), tank)->gasmix;
+				struct gasmix mix = state->cur_dive.get()->get_cylinder(tank)->gasmix;
 				int o2 = get_o2(mix);
 				int he = get_he(mix);
 
diff --git a/core/planner.cpp b/core/planner.cpp
index 24dbd07b9..3d03e2534 100644
--- a/core/planner.cpp
+++ b/core/planner.cpp
@@ -89,7 +89,7 @@ int get_cylinderid_at_time(struct dive *dive, struct divecomputer *dc, duration_
 		if (event.time.seconds > time.seconds)
 			break;
 		if (event.name == "gaschange")
-			cylinder_idx = get_cylinder_index(dive, event);
+			cylinder_idx = dive->get_cylinder_index(event);
 	}
 	return cylinder_idx;
 }
@@ -136,7 +136,7 @@ static int tissue_at_end(struct deco_state *ds, struct dive *dive, const struct
 						: sample.setpoint;
 
 		duration_t t1 = sample.time;
-		struct gasmix gas = get_gasmix_at_time(*dive, *dc, t0);
+		struct gasmix gas = dive->get_gasmix_at_time(*dc, t0);
 		if (psample)
 			lastdepth = psample->depth;
 
@@ -259,7 +259,7 @@ static void create_dive_from_plan(struct diveplan *diveplan, struct dive *dive,
 		if (dp->cylinderid != lastcylid) {
 			/* need to insert a first sample for the new gas */
 			add_gas_switch_event(dive, dc, lasttime + 1, dp->cylinderid);
-			cyl = get_cylinder(dive, dp->cylinderid); // FIXME: This actually may get one past the last cylinder for "surface air".
+			cyl = dive->get_cylinder(dp->cylinderid); // FIXME: This actually may get one past the last cylinder for "surface air".
 			if (!cyl) {
 				report_error("Invalid cylinder in create_dive_from_plan(): %d", dp->cylinderid);
 				continue;
@@ -368,7 +368,7 @@ struct gaschanges {
 
 static int setpoint_change(struct dive *dive, int cylinderid)
 {
-	cylinder_t *cylinder = get_cylinder(dive, cylinderid);
+	cylinder_t *cylinder = dive->get_cylinder(cylinderid);
 	if (cylinder->type.description.empty())
 		return 0;
 	if (starts_with(cylinder->type.description, "SP ")) {
@@ -422,7 +422,7 @@ static std::vector<gaschanges> analyze_gaslist(struct diveplan *diveplan, struct
 	for (size_t nr = 0; nr < gaschanges.size(); nr++) {
 		int idx = gaschanges[nr].gasidx;
 		printf("gaschange nr %d: @ %5.2lfm gasidx %d (%s)\n", nr, gaschanges[nr].depth / 1000.0,
-		       idx, gasname(&get_cylinder(&dive, idx)->gasmix));
+		       idx, gasname(&dive.get_cylinder(idx)->gasmix));
 	}
 #endif
 	return gaschanges;
@@ -507,7 +507,7 @@ int ascent_velocity(int depth, int avg_depth, int)
 
 static void track_ascent_gas(int depth, struct dive *dive, int cylinder_id, int avg_depth, int bottom_time, bool safety_stop, enum divemode_t divemode)
 {
-	cylinder_t *cylinder = get_cylinder(dive, cylinder_id);
+	cylinder_t *cylinder = dive->get_cylinder(cylinder_id);
 	while (depth > 0) {
 		int deltad = ascent_velocity(depth, avg_depth, bottom_time) * base_timestep;
 		if (deltad > depth)
@@ -575,7 +575,7 @@ static bool enough_gas(const struct dive *dive, int current_cylinder)
 {
 	if (current_cylinder < 0 || static_cast<size_t>(current_cylinder) >= dive->cylinders.size())
 		return false;
-	const cylinder_t *cyl = get_cylinder(dive, current_cylinder);
+	const cylinder_t *cyl = dive->get_cylinder(current_cylinder);
 
 	if (!cyl->start.mbar)
 		return true;
@@ -718,7 +718,7 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 	// Find the divemode at the end of the dive
 	divemode_loop loop(*dc);
 	divemode = loop.next(bottom_time);
-	gas = get_cylinder(dive, current_cylinder)->gasmix;
+	gas = dive->get_cylinder(current_cylinder)->gasmix;
 
 	po2 = sample.setpoint.mbar;
 	depth = sample.depth.mm;
@@ -768,11 +768,11 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 		// How long can we stay at the current depth and still directly ascent to the surface?
 		do {
 			add_segment(ds, dive->depth_to_bar(depth),
-				    get_cylinder(dive, current_cylinder)->gasmix,
+				    dive->get_cylinder(current_cylinder)->gasmix,
 				    timestep, po2, divemode, prefs.bottomsac, true);
-			update_cylinder_pressure(dive, depth, depth, timestep, prefs.bottomsac, get_cylinder(dive, current_cylinder), false, divemode);
+			update_cylinder_pressure(dive, depth, depth, timestep, prefs.bottomsac, dive->get_cylinder(current_cylinder), false, divemode);
 			clock += timestep;
-		} while (trial_ascent(ds, 0, depth, 0, avg_depth, bottom_time, get_cylinder(dive, current_cylinder)->gasmix,
+		} while (trial_ascent(ds, 0, depth, 0, avg_depth, bottom_time, dive->get_cylinder(current_cylinder)->gasmix,
 				      po2, diveplan->surface_pressure / 1000.0, dive, divemode) &&
 			 enough_gas(dive, current_cylinder) && clock < 6 * 3600);
 
@@ -780,7 +780,7 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 		// In the best of all worlds, we would roll back also the last add_segment in terms of caching deco state, but
 		// let's ignore that since for the eventual ascent in recreational mode, nobody looks at the ceiling anymore,
 		// so we don't really have to compute the deco state.
-		update_cylinder_pressure(dive, depth, depth, -timestep, prefs.bottomsac, get_cylinder(dive, current_cylinder), false, divemode);
+		update_cylinder_pressure(dive, depth, depth, -timestep, prefs.bottomsac, dive->get_cylinder(current_cylinder), false, divemode);
 		clock -= timestep;
 		plan_add_segment(diveplan, clock - previous_point_time, depth, current_cylinder, po2, true, divemode);
 		previous_point_time = clock;
@@ -816,7 +816,7 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 
 	if (best_first_ascend_cylinder != -1 && best_first_ascend_cylinder != current_cylinder) {
 		current_cylinder = best_first_ascend_cylinder;
-		gas = get_cylinder(dive, current_cylinder)->gasmix;
+		gas = dive->get_cylinder(current_cylinder)->gasmix;
 
 #if DEBUG_PLAN & 16
 		printf("switch to gas %d (%d/%d) @ %5.2lfm\n", best_first_ascend_cylinder,
@@ -831,7 +831,7 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 		po2 = 0;
 		int bailoutsegment = std::max(prefs.min_switch_duration, 60 * prefs.problemsolvingtime);
 		add_segment(ds, dive->depth_to_bar(depth),
-			get_cylinder(dive, current_cylinder)->gasmix,
+			dive->get_cylinder(current_cylinder)->gasmix,
 			bailoutsegment, po2, divemode, prefs.bottomsac, true);
 		plan_add_segment(diveplan, bailoutsegment, depth, current_cylinder, po2, false, divemode);
 		bottom_time += bailoutsegment;
@@ -871,7 +871,7 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 		last_ascend_rate = ascent_velocity(depth, avg_depth, bottom_time);
 		/* Always prefer the best_first_ascend_cylinder if it has the right gasmix.
 		 * Otherwise take first cylinder from list with rightgasmix  */
-		if (best_first_ascend_cylinder != -1 && same_gasmix(gas, get_cylinder(dive, best_first_ascend_cylinder)->gasmix))
+		if (best_first_ascend_cylinder != -1 && same_gasmix(gas, dive->get_cylinder(best_first_ascend_cylinder)->gasmix))
 			current_cylinder = best_first_ascend_cylinder;
 		else
 			current_cylinder = get_gasidx(dive, gas);
@@ -896,7 +896,7 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 					deltad = depth - stoplevels[stopidx];
 
 				add_segment(ds, dive->depth_to_bar(depth),
-								get_cylinder(dive, current_cylinder)->gasmix,
+								dive->get_cylinder(current_cylinder)->gasmix,
 								base_timestep, po2, divemode, prefs.decosac, true);
 				last_segment_min_switch = false;
 				clock += base_timestep;
@@ -921,7 +921,7 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 				if (current_cylinder != gaschanges[gi].gasidx) {
 					if (!prefs.switch_at_req_stop ||
 							!trial_ascent(ds, 0, depth, stoplevels[stopidx - 1], avg_depth, bottom_time,
-							get_cylinder(dive, current_cylinder)->gasmix, po2, diveplan->surface_pressure / 1000.0, dive, divemode) || get_o2(get_cylinder(dive, current_cylinder)->gasmix) < 160) {
+							dive->get_cylinder(current_cylinder)->gasmix, po2, diveplan->surface_pressure / 1000.0, dive, divemode) || get_o2(dive->get_cylinder(current_cylinder)->gasmix) < 160) {
 						if (is_final_plan)
 							plan_add_segment(diveplan, clock - previous_point_time, depth, current_cylinder, po2, false, divemode);
 						stopping = true;
@@ -930,14 +930,14 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 						if (divemode == CCR)
 							po2 = setpoint_change(dive, current_cylinder);
 #if DEBUG_PLAN & 16
-						gas = get_cylinder(dive, current_cylinder)->gasmix;
+						gas = dive->get_cylinder(current_cylinder)->gasmix;
 						printf("switch to gas %d (%d/%d) @ %5.2lfm\n", gaschanges[gi].gasidx,
 							(get_o2(&gas) + 5) / 10, (get_he(&gas) + 5) / 10, gaschanges[gi].depth / 1000.0);
 #endif
 						/* Stop for the minimum duration to switch gas unless we switch to o2 */
-						if (!last_segment_min_switch && get_o2(get_cylinder(dive, current_cylinder)->gasmix) != 1000) {
+						if (!last_segment_min_switch && get_o2(dive->get_cylinder(current_cylinder)->gasmix) != 1000) {
 							add_segment(ds, dive->depth_to_bar(depth),
-								get_cylinder(dive, current_cylinder)->gasmix,
+								dive->get_cylinder(current_cylinder)->gasmix,
 								prefs.min_switch_duration, po2, divemode, prefs.decosac, true);
 							clock += prefs.min_switch_duration;
 							last_segment_min_switch = true;
@@ -957,7 +957,7 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 			while (1) {
 				/* Check if ascending to next stop is clear, go back and wait if we hit the ceiling on the way */
 				if (trial_ascent(ds, 0, depth, stoplevels[stopidx], avg_depth, bottom_time,
-						get_cylinder(dive, current_cylinder)->gasmix, po2, diveplan->surface_pressure / 1000.0, dive, divemode)) {
+						dive->get_cylinder(current_cylinder)->gasmix, po2, diveplan->surface_pressure / 1000.0, dive, divemode)) {
 					decostoptable[decostopcounter].depth = depth;
 					decostoptable[decostopcounter].time = 0;
 					decostopcounter++;
@@ -986,14 +986,14 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 					if (divemode == CCR)
 						po2 = setpoint_change(dive, current_cylinder);
 #if DEBUG_PLAN & 16
-					gas = get_cylinder(dive, current_cylinder)->gasmix;
+					gas = dive->get_cylinder(current_cylinder)->gasmix;
 					printf("switch to gas %d (%d/%d) @ %5.2lfm\n", gaschanges[gi + 1].gasidx,
 						(get_o2(&gas) + 5) / 10, (get_he(&gas) + 5) / 10, gaschanges[gi + 1].depth / 1000.0);
 #endif
 					/* Stop for the minimum duration to switch gas unless we switch to o2 */
-					if (!last_segment_min_switch && get_o2(get_cylinder(dive, current_cylinder)->gasmix) != 1000) {
+					if (!last_segment_min_switch && get_o2(dive->get_cylinder(current_cylinder)->gasmix) != 1000) {
 						add_segment(ds, dive->depth_to_bar(depth),
-							get_cylinder(dive, current_cylinder)->gasmix,
+							dive->get_cylinder(current_cylinder)->gasmix,
 							prefs.min_switch_duration, po2, divemode, prefs.decosac, true);
 						clock += prefs.min_switch_duration;
 					}
@@ -1001,7 +1001,7 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 				}
 
 				int new_clock = wait_until(ds, dive, clock, clock, laststoptime * 2 + 1, timestep, depth, stoplevels[stopidx], avg_depth,
-					bottom_time, get_cylinder(dive, current_cylinder)->gasmix, po2, diveplan->surface_pressure / 1000.0, divemode);
+					bottom_time, dive->get_cylinder(current_cylinder)->gasmix, po2, diveplan->surface_pressure / 1000.0, divemode);
 				laststoptime = new_clock - clock;
 				/* Finish infinite deco */
 				if (laststoptime >= 48 * 3600 && depth >= 6000) {
@@ -1016,12 +1016,12 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 					 * backgas.  This could be customized if there were demand.
 					 */
 					if (break_cylinder == -1) {
-						if (best_first_ascend_cylinder != -1 && get_o2(get_cylinder(dive, best_first_ascend_cylinder)->gasmix) <= 320)
+						if (best_first_ascend_cylinder != -1 && get_o2(dive->get_cylinder(best_first_ascend_cylinder)->gasmix) <= 320)
 							break_cylinder = best_first_ascend_cylinder;
 						else
 							break_cylinder = 0;
 					}
-					if (get_o2(get_cylinder(dive, current_cylinder)->gasmix) == 1000) {
+					if (get_o2(dive->get_cylinder(current_cylinder)->gasmix) == 1000) {
 						if (laststoptime >= 12 * 60) {
 							laststoptime = 12 * 60;
 							new_clock = clock + laststoptime;
@@ -1046,7 +1046,7 @@ bool plan(struct deco_state *ds, struct diveplan *diveplan, struct dive *dive, i
 						}
 					}
 				}
-				add_segment(ds, dive->depth_to_bar(depth), get_cylinder(dive, stop_cylinder)->gasmix,
+				add_segment(ds, dive->depth_to_bar(depth), dive->get_cylinder(stop_cylinder)->gasmix,
 					    laststoptime, po2, divemode, prefs.decosac, true);
 				last_segment_min_switch = false;
 				decostoptable[decostopcounter].depth = depth;
diff --git a/core/plannernotes.cpp b/core/plannernotes.cpp
index 6790b6321..5f2669c81 100644
--- a/core/plannernotes.cpp
+++ b/core/plannernotes.cpp
@@ -191,13 +191,13 @@ void add_plan_to_notes(struct diveplan *diveplan, struct dive *dive, bool show_d
 		nextdp = dp->next;
 		if (dp->time == 0)
 			continue;
-		gasmix = get_cylinder(dive, dp->cylinderid)->gasmix;
+		gasmix = dive->get_cylinder(dp->cylinderid)->gasmix;
 		depthvalue = get_depth_units(dp->depth.mm, &decimals, &depth_unit);
 		/* analyze the dive points ahead */
 		while (nextdp && nextdp->time == 0)
 			nextdp = nextdp->next;
 		if (nextdp)
-			newgasmix = get_cylinder(dive, nextdp->cylinderid)->gasmix;
+			newgasmix = dive->get_cylinder(nextdp->cylinderid)->gasmix;
 		gaschange_after = (nextdp && (gasmix_distance(gasmix, newgasmix)));
 		gaschange_before =  (gasmix_distance(lastprintgasmix, gasmix));
 		rebreatherchange_after = (nextdp && (dp->setpoint != nextdp->setpoint || dp->divemode != nextdp->divemode));
@@ -577,7 +577,7 @@ void add_plan_to_notes(struct diveplan *diveplan, struct dive *dive, bool show_d
 			while (dp) {
 				if (dp->time != 0) {
 					std::string temp;
-					struct gasmix gasmix = get_cylinder(dive, dp->cylinderid)->gasmix;
+					struct gasmix gasmix = dive->get_cylinder(dp->cylinderid)->gasmix;
 
 					divemode_t current_divemode = loop.next(dp->time);
 					amb = dive->depth_to_atm(dp->depth.mm);
diff --git a/core/profile.cpp b/core/profile.cpp
index e2c1b6281..599e38212 100644
--- a/core/profile.cpp
+++ b/core/profile.cpp
@@ -126,7 +126,7 @@ static int get_local_sac(struct plot_info &pi, int idx1, int idx2, struct dive *
 	depth = (entry1.depth + entry2.depth) / 2;
 	atm = dive->depth_to_atm(depth);
 
-	cyl = get_cylinder(dive, index);
+	cyl = dive->get_cylinder(index);
 
 	airuse = gas_volume(cyl, a) - gas_volume(cyl, b);
 
@@ -193,35 +193,6 @@ static void analyze_plot_info(struct plot_info &pi)
 	}
 }
 
-/*
- * If the event has an explicit cylinder index,
- * we return that. If it doesn't, we return the best
- * match based on the gasmix.
- *
- * Some dive computers give cylinder indices, some
- * give just the gas mix.
- */
-int get_cylinder_index(const struct dive *dive, const struct event &ev)
-{
-	int best;
-	struct gasmix mix;
-
-	if (ev.gas.index >= 0)
-		return ev.gas.index;
-
-	/*
-	 * This should no longer happen!
-	 *
-	 * We now match up gas change events with their cylinders at dive
-	 * event fixup time.
-	 */
-	report_info("Still looking up cylinder based on gas mix in get_cylinder_index()!");
-
-	mix = get_gasmix_from_event(dive, ev);
-	best = find_best_gasmix_match(mix, dive->cylinders);
-	return best < 0 ? 0 : best;
-}
-
 static size_t set_setpoint(struct plot_info &pi, size_t i, int setpoint, int end)
 {
 	while (i < pi.entry.size()) {
@@ -508,7 +479,7 @@ static int sac_between(const struct dive *dive, const struct plot_info &pi, int
 
 		a.mbar = get_plot_pressure(pi, first, i);
 		b.mbar = get_plot_pressure(pi, last, i);
-		const cylinder_t *cyl = get_cylinder(dive, i);
+		const cylinder_t *cyl = dive->get_cylinder(i);
 		int cyluse = gas_volume(cyl, a) - gas_volume(cyl, b);
 		if (cyluse > 0)
 			airuse += cyluse;
@@ -704,7 +675,7 @@ static void setup_gas_sensor_pressure(const struct dive *dive, const struct dive
 	std::vector<int> first(num_cyl, 0);
 	std::vector<int> last(num_cyl, INT_MAX);
 
-	int prev = explicit_first_cylinder(dive, dc);
+	int prev = dive->explicit_first_cylinder(dc);
 	prev = prev >= 0 ? prev : 0;
 	seen[prev] = 1;
 
@@ -735,7 +706,7 @@ static void setup_gas_sensor_pressure(const struct dive *dive, const struct dive
 	// Fill in "seen[]" array - mark cylinders we're not interested
 	// in as negative.
 	for (int i = 0; i < pi.nr_cylinders; i++) {
-		const cylinder_t *cyl = get_cylinder(dive, i);
+		const cylinder_t *cyl = dive->get_cylinder(i);
 		int start = cyl->start.mbar;
 		int end = cyl->end.mbar;
 
@@ -756,7 +727,7 @@ static void setup_gas_sensor_pressure(const struct dive *dive, const struct dive
 
 		/* If it's only mentioned by other dc's, ignore it */
 		for (auto &secondary: dive->dcs) {
-			if (has_gaschange_event(dive, &secondary, i)) {
+			if (dive->has_gaschange_event(&secondary, i)) {
 				seen[i] = -1;
 				break;
 			}
@@ -765,7 +736,7 @@ static void setup_gas_sensor_pressure(const struct dive *dive, const struct dive
 
 	for (int i = 0; i < pi.nr_cylinders; i++) {
 		if (seen[i] >= 0) {
-			const cylinder_t *cyl = get_cylinder(dive, i);
+			const cylinder_t *cyl = dive->get_cylinder(i);
 
 			add_plot_pressure(pi, first[i], i, cyl->start);
 			add_plot_pressure(pi, last[i], i, cyl->end);
@@ -1306,7 +1277,7 @@ static std::vector<std::string> plot_string(const struct dive *d, const struct p
 		int mbar = get_plot_pressure(pi, idx, cyl);
 		if (!mbar)
 			continue;
-		struct gasmix mix = get_cylinder(d, cyl)->gasmix;
+		struct gasmix mix = d->get_cylinder(cyl)->gasmix;
 		pressurevalue = get_pressure_units(mbar, &pressure_unit);
 		res.push_back(casprintf_loc(translate("gettextFromC", "P: %d%s (%s)"), pressurevalue, pressure_unit, gasname(mix)));
 	}
@@ -1531,7 +1502,7 @@ std::vector<std::string> compare_samples(const struct dive *d, const struct plot
 				if (last_pressures[cylinder_index]) {
 					bar_used[cylinder_index] += last_pressures[cylinder_index] - next_pressure;
 
-					const cylinder_t *cyl = get_cylinder(d, cylinder_index);
+					const cylinder_t *cyl = d->get_cylinder(cylinder_index);
 
 					volumes_used[cylinder_index] += gas_volume(cyl, (pressure_t){ last_pressures[cylinder_index] }) - gas_volume(cyl, (pressure_t){ next_pressure });
 				}
@@ -1584,7 +1555,7 @@ std::vector<std::string> compare_samples(const struct dive *d, const struct plot
 			total_bar_used += bar_used[cylinder_index];
 			total_volume_used += volumes_used[cylinder_index];
 
-			const cylinder_t *cyl = get_cylinder(d, cylinder_index);
+			const cylinder_t *cyl = d->get_cylinder(cylinder_index);
 			if (cyl->type.size.mliter) {
 				if (cylinder_volume.mliter && cylinder_volume.mliter != cyl->type.size.mliter) {
 					cylindersizes_are_identical = false;
diff --git a/core/qthelper.cpp b/core/qthelper.cpp
index 8d7b334ea..1b4337875 100644
--- a/core/qthelper.cpp
+++ b/core/qthelper.cpp
@@ -351,7 +351,7 @@ QVector<QPair<QString, int>> selectedDivesGasUsed()
 		std::vector<volume_t> diveGases = get_gas_used(d);
 		for (size_t j = 0; j < d->cylinders.size(); j++) {
 			if (diveGases[j].mliter) {
-				QString gasName = gasname(get_cylinder(d, j)->gasmix);
+				QString gasName = gasname(d->get_cylinder(j)->gasmix);
 				gasUsed[gasName] += diveGases[j].mliter;
 			}
 		}
diff --git a/core/save-git.cpp b/core/save-git.cpp
index 7df5c7637..9a6eaf6a3 100644
--- a/core/save-git.cpp
+++ b/core/save-git.cpp
@@ -385,7 +385,7 @@ static void save_one_event(struct membuffer *b, const struct dive &dive, const s
 		show_index(b, ev.value, "value=", "");
 	show_utf8(b, " name=", ev.name.c_str(), "");
 	if (ev.is_gaschange()) {
-		struct gasmix mix = get_gasmix_from_event(&dive, ev);
+		struct gasmix mix = dive.get_gasmix_from_event(ev);
 		if (ev.gas.index >= 0)
 			show_integer(b, ev.gas.index, "cylinder=", "");
 		put_gasmix(b, mix);
diff --git a/core/save-xml.cpp b/core/save-xml.cpp
index 69c7a4920..a7b034aeb 100644
--- a/core/save-xml.cpp
+++ b/core/save-xml.cpp
@@ -352,7 +352,7 @@ static void save_one_event(struct membuffer *b, const struct dive &dive, const s
 		show_index(b, ev.value, "value='", "'");
 	show_utf8(b, ev.name.c_str(), " name='", "'", 1);
 	if (ev.is_gaschange()) {
-		struct gasmix mix = get_gasmix_from_event(&dive, ev);
+		struct gasmix mix = dive.get_gasmix_from_event(ev);
 		if (ev.gas.index >= 0)
 			show_integer(b, ev.gas.index, "cylinder='", "'");
 		put_gasmix(b, mix);
diff --git a/core/statistics.cpp b/core/statistics.cpp
index 55b2538aa..3b7569707 100644
--- a/core/statistics.cpp
+++ b/core/statistics.cpp
@@ -249,51 +249,6 @@ stats_t calculate_stats_selected()
 
 #define SOME_GAS 5000 // 5bar drop in cylinder pressure makes cylinder used
 
-bool has_gaschange_event(const struct dive *dive, const struct divecomputer *dc, int idx)
-{
-	bool first_gas_explicit = false;
-	event_loop loop("gaschange");
-	while (auto event = loop.next(*dc)) {
-		if (!dc->samples.empty() && (event->time.seconds == 0 ||
-				   (dc->samples[0].time.seconds == event->time.seconds)))
-			first_gas_explicit = true;
-		if (get_cylinder_index(dive, *event) == idx)
-			return true;
-	}
-	return !first_gas_explicit && idx == 0;
-}
-
-bool is_cylinder_used(const struct dive *dive, int idx)
-{
-	if (idx < 0 || static_cast<size_t>(idx) >= dive->cylinders.size())
-		return false;
-
-	const cylinder_t &cyl = dive->cylinders[idx];
-	if ((cyl.start.mbar - cyl.end.mbar) > SOME_GAS)
-		return true;
-
-	if ((cyl.sample_start.mbar - cyl.sample_end.mbar) > SOME_GAS)
-		return true;
-
-	for (auto &dc: dive->dcs) {
-		if (has_gaschange_event(dive, &dc, idx))
-			return true;
-		else if (dc.divemode == CCR && idx == get_cylinder_idx_by_use(dive, OXYGEN))
-			return true;
-	}
-	return false;
-}
-
-bool is_cylinder_prot(const struct dive *dive, int idx)
-{
-	if (idx < 0 || static_cast<size_t>(idx) >= dive->cylinders.size())
-		return false;
-
-	return std::any_of(dive->dcs.begin(), dive->dcs.end(),
-			   [dive, idx](auto &dc)
-			   { return has_gaschange_event(dive, &dc, idx); });
-}
-
 /* Returns a vector with dive->cylinders.size() entries */
 std::vector<volume_t> get_gas_used(struct dive *dive)
 {
@@ -334,7 +289,7 @@ std::pair<volume_t, volume_t> selected_dives_gas_parts()
 		int j = 0;
 		for (auto &gas: get_gas_used(d.get())) {
 			if (gas.mliter) {
-				auto [o2, he] = get_gas_parts(get_cylinder(d.get(), j)->gasmix, gas, O2_IN_AIR);
+				auto [o2, he] = get_gas_parts(d->get_cylinder(j)->gasmix, gas, O2_IN_AIR);
 				o2_tot.mliter += o2.mliter;
 				he_tot.mliter += he.mliter;
 			}
diff --git a/core/string-format.cpp b/core/string-format.cpp
index b97732824..f3d5b6ce6 100644
--- a/core/string-format.cpp
+++ b/core/string-format.cpp
@@ -79,7 +79,7 @@ QStringList formatGetCylinder(const dive *d)
 {
 	QStringList getCylinder;
 	for (auto [i, cyl]: enumerated_range(d->cylinders)) {
-		if (is_cylinder_used(d, i))
+		if (d->is_cylinder_used(i))
 			getCylinder << QString::fromStdString(cyl.type.description);
 	}
 	return getCylinder;
@@ -89,7 +89,7 @@ QStringList formatStartPressure(const dive *d)
 {
 	QStringList startPressure;
 	for (auto [i, cyl]: enumerated_range(d->cylinders)) {
-		if (is_cylinder_used(d, i))
+		if (d->is_cylinder_used(i))
 			startPressure << getPressures(cyl, START_PRESSURE);
 	}
 	return startPressure;
@@ -99,7 +99,7 @@ QStringList formatEndPressure(const dive *d)
 {
 	QStringList endPressure;
 	for (auto [i, cyl]: enumerated_range(d->cylinders)) {
-		if (is_cylinder_used(d, i))
+		if (d->is_cylinder_used(i))
 			endPressure << getPressures(cyl, END_PRESSURE);
 	}
 	return endPressure;
@@ -109,7 +109,7 @@ QStringList formatFirstGas(const dive *d)
 {
 	QStringList gas;
 	for (auto [i, cyl]: enumerated_range(d->cylinders)) {
-		if (is_cylinder_used(d, i))
+		if (d->is_cylinder_used(i))
 			gas << get_gas_string(cyl.gasmix);
 	}
 	return gas;
@@ -174,7 +174,7 @@ QString formatGas(const dive *d)
 	 */
 	QString gases;
 	for (auto [i, cyl]: enumerated_range(d->cylinders)) {
-		if (!is_cylinder_used(d, i))
+		if (!d->is_cylinder_used(i))
 			continue;
 		QString gas = QString::fromStdString(cyl.type.description);
 		if (!gas.isEmpty())
diff --git a/desktop-widgets/simplewidgets.cpp b/desktop-widgets/simplewidgets.cpp
index 16dae6a5e..650db6a6e 100644
--- a/desktop-widgets/simplewidgets.cpp
+++ b/desktop-widgets/simplewidgets.cpp
@@ -346,7 +346,7 @@ void DiveComponentSelection::buttonClicked(QAbstractButton *button)
 		if (what->cylinders) {
 			text << tr("Cylinders:\n");
 			for (auto [idx, cyl]: enumerated_range(current_dive->cylinders)) {
-				if (is_cylinder_used(current_dive, idx))
+				if (current_dive->is_cylinder_used(idx))
 					text << QString::fromStdString(cyl.type.description) << " " << gasname(cyl.gasmix) << "\n";
 			}
 		}
diff --git a/desktop-widgets/tab-widgets/TabDiveInformation.cpp b/desktop-widgets/tab-widgets/TabDiveInformation.cpp
index b73f05204..8dec4d510 100644
--- a/desktop-widgets/tab-widgets/TabDiveInformation.cpp
+++ b/desktop-widgets/tab-widgets/TabDiveInformation.cpp
@@ -134,12 +134,12 @@ void TabDiveInformation::updateProfile()
 	QString gaslist, SACs, separator;
 
 	for (size_t i = 0; i < currentDive->cylinders.size(); i++) {
-		if (!is_cylinder_used(currentDive, i))
+		if (!currentDive->is_cylinder_used(i))
 			continue;
 		gaslist.append(separator); volumes.append(separator); SACs.append(separator);
 		separator = "\n";
 
-		gaslist.append(gasname(get_cylinder(currentDive, i)->gasmix));
+		gaslist.append(gasname(currentDive->get_cylinder(i)->gasmix));
 		if (!gases[i].mliter)
 			continue;
 		volumes.append(get_volume_string(gases[i], true));
diff --git a/mobile-widgets/qmlmanager.cpp b/mobile-widgets/qmlmanager.cpp
index 83c5ae065..b0f83c4be 100644
--- a/mobile-widgets/qmlmanager.cpp
+++ b/mobile-widgets/qmlmanager.cpp
@@ -1242,7 +1242,7 @@ void QMLManager::commitChanges(QString diveId, QString number, QString date, QSt
 	if (formatStartPressure(d) != startpressure || formatEndPressure(d) != endpressure) {
 		diveChanged = true;
 		for ( int i = 0, j = 0 ; j < startpressure.length() && j < endpressure.length() ; i++ ) {
-			if (state != "add" && !is_cylinder_used(d, i))
+			if (state != "add" && !d->is_cylinder_used(i))
 				continue;
 
 			cylinder_t *cyl = get_or_create_cylinder(d, i);
@@ -1257,7 +1257,7 @@ void QMLManager::commitChanges(QString diveId, QString number, QString date, QSt
 	// gasmix for first cylinder
 	if (formatFirstGas(d) != gasmix) {
 		for ( int i = 0, j = 0 ; j < gasmix.length() ; i++ ) {
-			if (state != "add" && !is_cylinder_used(d, i))
+			if (state != "add" && !d->is_cylinder_used(i))
 				continue;
 
 			int o2 = parseGasMixO2(gasmix[j]);
@@ -1268,7 +1268,7 @@ void QMLManager::commitChanges(QString diveId, QString number, QString date, QSt
 				o2 + he <= 1000) {
 				diveChanged = true;
 				get_or_create_cylinder(d, i)->gasmix.o2.permille = o2;
-				get_cylinder(d, i)->gasmix.he.permille = he;
+				d->get_cylinder(i)->gasmix.he.permille = he;
 			}
 			j++;
 		}
@@ -1278,7 +1278,7 @@ void QMLManager::commitChanges(QString diveId, QString number, QString date, QSt
 		diveChanged = true;
 		int size = 0, wp = 0, j = 0, k = 0;
 		for (j = 0; k < usedCylinder.length(); j++) {
-			if (state != "add" && !is_cylinder_used(d, j))
+			if (state != "add" && !d->is_cylinder_used(j))
 				continue;
 
 			for (const tank_info &ti: tank_info_table) {
@@ -1294,8 +1294,8 @@ void QMLManager::commitChanges(QString diveId, QString number, QString date, QSt
 				}
 			}
 			get_or_create_cylinder(d, j)->type.description = usedCylinder[k].toStdString();
-			get_cylinder(d, j)->type.size.mliter = size;
-			get_cylinder(d, j)->type.workingpressure.mbar = wp;
+			d->get_cylinder(j)->type.size.mliter = size;
+			d->get_cylinder(j)->type.workingpressure.mbar = wp;
 			k++;
 		}
 	}
diff --git a/profile-widget/diveeventitem.cpp b/profile-widget/diveeventitem.cpp
index cc1b49f73..a52090541 100644
--- a/profile-widget/diveeventitem.cpp
+++ b/profile-widget/diveeventitem.cpp
@@ -51,7 +51,7 @@ void DiveEventItem::setupPixmap(struct gasmix lastgasmix, const DivePixmaps &pix
 		setPixmap(pixmaps.bookmark);
 		setOffset(QPointF(0.0, -pixmap().height()));
 	} else if (ev.is_gaschange()) {
-		struct gasmix mix = get_gasmix_from_event(dive, ev);
+		struct gasmix mix = dive->get_gasmix_from_event(ev);
 		struct icd_data icd_data;
 		bool icd = isobaric_counterdiffusion(lastgasmix, mix, &icd_data);
 		if (mix.he.permille) {
@@ -123,7 +123,7 @@ void DiveEventItem::setupToolTipString(struct gasmix lastgasmix)
 
 	if (ev.is_gaschange()) {
 		struct icd_data icd_data;
-		struct gasmix mix = get_gasmix_from_event(dive, ev);
+		struct gasmix mix = dive->get_gasmix_from_event(ev);
 		name += ": ";
 		name += gasname(mix);
 
diff --git a/profile-widget/diveprofileitem.cpp b/profile-widget/diveprofileitem.cpp
index a4573c8b1..18ab08ead 100644
--- a/profile-widget/diveprofileitem.cpp
+++ b/profile-widget/diveprofileitem.cpp
@@ -602,9 +602,7 @@ void DiveGasPressureItem::replot(const dive *d, int fromIn, int toIn, bool in_pl
 
 	bool showDescriptions = false;
 	for (int cyl = 0; cyl < pInfo.nr_cylinders; cyl++) {
-		const cylinder_t *c = get_cylinder(d, cyl);
-		if (!c)
-			continue;
+		const cylinder_t *c = d->get_cylinder(cyl);
 		showDescriptions = showDescriptions || (c && same_gasmix_cylinder(*c, cyl, d, true) != -1);
 		if (act_segments[cyl].polygon.empty())
 			continue;
@@ -634,7 +632,7 @@ void DiveGasPressureItem::replot(const dive *d, int fromIn, int toIn, bool in_pl
 
 		// For each cylinder, on right hand side of the curve, write cylinder pressure
 		double x_offset = plotPressureValue(segment.last.pressure, segment.last.time, Qt::AlignTop | Qt::AlignLeft, y_offset) + 2;
-		plotGasValue(segment.last.pressure, segment.last.time, get_cylinder(d, segment.cyl), Qt::AlignTop | Qt::AlignLeft, x_offset, y_offset, showDescriptions);
+		plotGasValue(segment.last.pressure, segment.last.time, d->get_cylinder(segment.cyl), Qt::AlignTop | Qt::AlignLeft, x_offset, y_offset, showDescriptions);
 
 		/* Alternate alignment as we see cylinder use.. */
 		startAlignVar ^= Qt::AlignTop | Qt::AlignBottom;
diff --git a/profile-widget/profilescene.cpp b/profile-widget/profilescene.cpp
index 94ed17860..031d6160e 100644
--- a/profile-widget/profilescene.cpp
+++ b/profile-widget/profilescene.cpp
@@ -551,7 +551,7 @@ void ProfileScene::plotDive(const struct dive *dIn, int dcIn, DivePlannerPointsM
 	// while all other items are up there on the constructor.
 	qDeleteAll(eventItems);
 	eventItems.clear();
-	struct gasmix lastgasmix = get_gasmix_at_time(*d, *currentdc, duration_t{1});
+	struct gasmix lastgasmix = d->get_gasmix_at_time(*currentdc, duration_t{1});
 
 	for (auto [idx, event]: enumerated_range(currentdc->events)) {
 		// if print mode is selected only draw headings, SP change, gas events or bookmark event
@@ -571,7 +571,7 @@ void ProfileScene::plotDive(const struct dive *dIn, int dcIn, DivePlannerPointsM
 			eventItems.push_back(item);
 		}
 		if (event.is_gaschange())
-			lastgasmix = get_gasmix_from_event(d, event);
+			lastgasmix = d->get_gasmix_from_event(event);
 	}
 
 	QString dcText = QString::fromStdString(get_dc_nickname(currentdc));
diff --git a/profile-widget/profilewidget2.cpp b/profile-widget/profilewidget2.cpp
index f8a9159dd..aa0386391 100644
--- a/profile-widget/profilewidget2.cpp
+++ b/profile-widget/profilewidget2.cpp
@@ -614,7 +614,7 @@ void ProfileWidget2::contextMenuEvent(QContextMenuEvent *event)
 			if (gasChangeIdx < plotInfo.nr - 1) {
 				int newGasIdx = gasChangeIdx + 1;
 				const struct plot_data &newGasEntry = plotInfo.entry[newGasIdx];
-				if (get_plot_sensor_pressure(&plotInfo, gasChangeIdx) == 0 || get_cylinder(d, gasChangeEntry->sensor[0])->sample_start.mbar == 0) {
+				if (get_plot_sensor_pressure(&plotInfo, gasChangeIdx) == 0 || d->get_cylinder(gasChangeEntry->sensor[0])->sample_start.mbar == 0) {
 					// if we have no sensorpressure or if we have no pressure from samples we can assume that
 					// we only have interpolated pressure (the pressure in the entry may be stored in the sensor
 					// pressure field if this is the first or last entry for this tank... see details in gaspressures.c
@@ -623,7 +623,7 @@ void ProfileWidget2::contextMenuEvent(QContextMenuEvent *event)
 					QAction *adjustOldPressure = m.addAction(tr("Adjust pressure of cyl. %1 (currently interpolated as %2)")
 										 .arg(gasChangeEntry->sensor[0] + 1).arg(get_pressure_string(pressure)));
 				}
-				if (get_plot_sensor_pressure(&plotInfo, newGasIdx) == 0 || get_cylinder(d, newGasEntry->sensor[0])->sample_start.mbar == 0) {
+				if (get_plot_sensor_pressure(&plotInfo, newGasIdx) == 0 || d->get_cylinder(newGasEntry->sensor[0])->sample_start.mbar == 0) {
 					// we only have interpolated press -- see commend above
 					pressure_t pressure;
 					pressure.mbar = get_plot_interpolated_pressure(&plotInfo, newGasIdx) ? : get_plot_sensor_pressure(&plotInfo, newGasIdx);
@@ -920,7 +920,7 @@ void ProfileWidget2::repositionDiveHandlers()
 		QPointF pos = line.pointAt(0.5);
 		gases[i]->setPos(pos);
 		if (datapoint.cylinderid >= 0 && datapoint.cylinderid < static_cast<int>(d->cylinders.size()))
-			gases[i]->setText(get_gas_string(get_cylinder(d, datapoint.cylinderid)->gasmix));
+			gases[i]->setText(get_gas_string(d->get_cylinder(datapoint.cylinderid)->gasmix));
 		else
 			gases[i]->setText(QString());
 		gases[i]->setVisible(datapoint.entered &&
diff --git a/profile-widget/tankitem.cpp b/profile-widget/tankitem.cpp
index e92a5b0d1..f8cc1aeb1 100644
--- a/profile-widget/tankitem.cpp
+++ b/profile-widget/tankitem.cpp
@@ -84,14 +84,14 @@ void TankItem::setData(const struct dive *d, const struct divecomputer *dc, int
 	struct gasmix gasmix = gasmix_invalid;
 	const struct event *ev;
 	while ((ev = loop.next(*dc)) != nullptr && ev->time.seconds <= plotStartTime)
-		gasmix = get_gasmix_from_event(d, *ev);
+		gasmix = d->get_gasmix_from_event(*ev);
 
 	// work through all the gas changes and add the rectangle for each gas while it was used
 	int startTime = plotStartTime;
 	while (ev && (int)ev->time.seconds < plotEndTime) {
 		createBar(startTime, ev->time.seconds, gasmix);
 		startTime = ev->time.seconds;
-		gasmix = get_gasmix_from_event(d, *ev);
+		gasmix = d->get_gasmix_from_event(*ev);
 		ev = loop.next(*dc);
 	}
 	createBar(startTime, plotEndTime, gasmix);
diff --git a/qt-models/cylindermodel.cpp b/qt-models/cylindermodel.cpp
index ef05471ce..033b21856 100644
--- a/qt-models/cylindermodel.cpp
+++ b/qt-models/cylindermodel.cpp
@@ -155,7 +155,7 @@ QVariant CylindersModel::data(const QModelIndex &index, int role) const
 		return QVariant();
 	}
 
-	const cylinder_t *cyl = index.row() == tempRow ? &tempCyl : get_cylinder(d, index.row());
+	const cylinder_t *cyl = index.row() == tempRow ? &tempCyl : d->get_cylinder(index.row());
 
 	switch (role) {
 	case Qt::BackgroundRole: {
@@ -259,7 +259,7 @@ QVariant CylindersModel::data(const QModelIndex &index, int role) const
 	case Qt::SizeHintRole:
 		if (index.column() == REMOVE) {
 			if ((inPlanner && DivePlannerPointsModel::instance()->tankInUse(index.row())) ||
-				(!inPlanner && is_cylinder_prot(d, index.row()))) {
+				(!inPlanner && d->is_cylinder_prot(index.row()))) {
 					return trashForbiddenIcon();
 			}
 			return trashIcon();
@@ -269,7 +269,7 @@ QVariant CylindersModel::data(const QModelIndex &index, int role) const
 		switch (index.column()) {
 		case REMOVE:
 			if ((inPlanner && DivePlannerPointsModel::instance()->tankInUse(index.row())) ||
-				(!inPlanner && is_cylinder_prot(d, index.row()))) {
+				(!inPlanner && d->is_cylinder_prot(index.row()))) {
 					return tr("This gas is in use. Only cylinders that are not used in the dive can be removed.");
 			}
 			return tr("Clicking here will remove this cylinder.");
@@ -301,7 +301,7 @@ cylinder_t *CylindersModel::cylinderAt(const QModelIndex &index)
 {
 	if (!d)
 		return nullptr;
-	return get_cylinder(d, index.row());
+	return d->get_cylinder(index.row());
 }
 
 bool CylindersModel::setData(const QModelIndex &index, const QVariant &value, int role)
@@ -364,7 +364,7 @@ bool CylindersModel::setData(const QModelIndex &index, const QVariant &value, in
 	// First, we make a shallow copy of the old cylinder. Then we modify the fields inside that copy.
 	// At the end, we either place an EditCylinder undo command (EquipmentTab) or copy the cylinder back (planner).
 	// Yes, this is not ideal, but the pragmatic thing to do for now.
-	cylinder_t cyl = *get_cylinder(d, row);
+	cylinder_t cyl = *d->get_cylinder(row);
 
 	if (index.column() != TYPE && !changed)
 		return false;
@@ -470,7 +470,7 @@ bool CylindersModel::setData(const QModelIndex &index, const QVariant &value, in
 
 	if (inPlanner) {
 		// In the planner - simply overwrite the cylinder in the dive with the modified cylinder.
-		*get_cylinder(d, row) = cyl;
+		*d->get_cylinder(row) = cyl;
 		dataChanged(index, index);
 	} else {
 		// On the EquipmentTab - place an editCylinder command.
@@ -711,7 +711,7 @@ void CylindersModel::initTempCyl(int row)
 	if (!d || tempRow == row)
 		return;
 	clearTempCyl();
-	const cylinder_t *cyl = get_cylinder(d, row);
+	const cylinder_t *cyl = d->get_cylinder(row);
 	if (!cyl)
 		return;
 
@@ -737,7 +737,7 @@ void CylindersModel::commitTempCyl(int row)
 		return;
 	if (row != tempRow)
 		return clearTempCyl(); // Huh? We are supposed to commit a different row than the one we stored?
-	cylinder_t *cyl = get_cylinder(d, tempRow);
+	cylinder_t *cyl = d->get_cylinder(tempRow);
 	if (!cyl)
 		return;
 	// Only submit a command if the type changed
diff --git a/smtk-import/smartrak.cpp b/smtk-import/smartrak.cpp
index 7c1efeec1..96b473e8c 100644
--- a/smtk-import/smartrak.cpp
+++ b/smtk-import/smartrak.cpp
@@ -507,7 +507,7 @@ static void merge_cylinder_info(cylinder_t *src, cylinder_t *dst)
 static void smtk_clean_cylinders(struct dive *d)
 {
 	int i = tanks - 1;
-	cylinder_t  *cyl, *base = get_cylinder(d, 0);
+	cylinder_t  *cyl, *base = d->get_cylinder(0);
 
 	cyl = base + tanks - 1;
 	while (cyl != base) {
diff --git a/tests/testplan.cpp b/tests/testplan.cpp
index 87b5804e3..63744fbd5 100644
--- a/tests/testplan.cpp
+++ b/tests/testplan.cpp
@@ -768,8 +768,7 @@ void TestPlan::testMultipleGases()
 	save_dive(stdout, dive, false);
 #endif
 
-	gasmix gas;
-	gas = get_gasmix_at_time(dive, dive.dcs[0], {20 * 60 + 1});
+	gasmix gas = dive.get_gasmix_at_time(dive.dcs[0], {20 * 60 + 1});
 	QCOMPARE(get_o2(gas), 110);
 	QVERIFY(compareDecoTime(dive.dcs[0].duration.seconds, 2480u, 2480u));
 }
@@ -963,17 +962,17 @@ void TestPlan::testCcrBailoutGasSelection()
 #endif
 
 	// check diluent used
-	cylinder_t *cylinder = get_cylinder(&dive, get_cylinderid_at_time(&dive, &dive.dcs[0], { 20 * 60 - 1 }));
+	cylinder_t *cylinder = dive.get_cylinder(get_cylinderid_at_time(&dive, &dive.dcs[0], { 20 * 60 - 1 }));
 	QCOMPARE(cylinder->cylinder_use, DILUENT);
 	QCOMPARE(get_o2(cylinder->gasmix), 200);
 
 	// check deep bailout used
-	cylinder = get_cylinder(&dive, get_cylinderid_at_time(&dive, &dive.dcs[0], { 20 * 60 + 1 }));
+	cylinder = dive.get_cylinder(get_cylinderid_at_time(&dive, &dive.dcs[0], { 20 * 60 + 1 }));
 	QCOMPARE(cylinder->cylinder_use, OC_GAS);
 	QCOMPARE(get_o2(cylinder->gasmix), 190);
 
 	// check shallow bailout used
-	cylinder = get_cylinder(&dive, get_cylinderid_at_time(&dive, &dive.dcs[0], { 30 * 60 }));
+	cylinder = dive.get_cylinder(get_cylinderid_at_time(&dive, &dive.dcs[0], { 30 * 60 }));
 	QCOMPARE(cylinder->cylinder_use, OC_GAS);
 	QCOMPARE(get_o2(cylinder->gasmix), 530);