2 files changed, 35 insertions, 0 deletions
diff --git a/core/qthelper.cpp b/core/qthelper.cpp
index 7b879e7d6..10e62eabe 100644
--- a/core/qthelper.cpp
+++ b/core/qthelper.cpp
@@ -1661,3 +1661,36 @@ extern "C" char *get_changes_made()
 	else
 		return nullptr;
 }
+
+// Generate a cylinder-renumber map for use when the n-th cylinder
+// of a dive with count cylinders is removed. It fills an int vector
+// with 0..n, -1, n..count-1. Each entry in the vector represents
+// the new id of the cylinder, whereby <0 means that this particular
+// cylinder does not get any new id. This should probably be moved
+// to the C-core, but using std::vector is simply more convenient.
+// The function assumes that n < count!
+std::vector<int> get_cylinder_map_for_remove(int count, int n)
+{
+	// 1) Fill mapping[0]..mapping[n-1] with 0..n-1
+	// 2) Set mapping[n] to -1
+	// 3) Fill mapping[n+1]..mapping[count-1] with n..count-2
+	std::vector<int> mapping(count);
+	std::iota(mapping.begin(), mapping.begin() + n, 0);
+	mapping[n] = -1;
+	std::iota(mapping.begin() + n + 1, mapping.end(), n);
+	return mapping;
+}
+
+// Generate a cylinder-renumber map for use when a cylinder is added
+// before the n-th cylinder. It fills an int vector with
+// with 0..n-1, n+1..count. Each entry in the vector represents
+// the new id of the cylinder. This probably should be moved
+// to the C-core, but using std::vector is simply more convenient.
+// This function assumes that that n <= count!
+std::vector<int> get_cylinder_map_for_add(int count, int n)
+{
+	std::vector<int> mapping(count);
+	std::iota(mapping.begin(), mapping.begin() + n, 0);
+	std::iota(mapping.begin() + n, mapping.end(), n + 1);
+	return mapping;
+}
diff --git a/core/qthelper.h b/core/qthelper.h
index bb8876383..848763138 100644
--- a/core/qthelper.h
+++ b/core/qthelper.h
@@ -83,6 +83,8 @@ QLocale getLocale();
 QVector<QPair<QString, int>> selectedDivesGasUsed();
 QString getUserAgent();
 QString printGPSCoords(const location_t *loc);
+std::vector<int> get_cylinder_map_for_remove(int count, int n);
+std::vector<int> get_cylinder_map_for_add(int count, int n);
 
 extern QString (*changesCallback)();
 void uiNotification(const QString &msg);