core: create range.h header for range manupulation functions

The moveInVector() function was defined in qthelper.h, even
though it has nothing to do with Qt. Therefore, move it into
its own header.

Morover, since it is a very low-level function, use snake_case.
And rename it to move_in_range(), because it does not only
work on vectors, but any range with random-access iterators.

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

core/range.h

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0
+// Helper functions for range manipulations
+#ifndef RANGE_H
+#define RANGE_H
+
+// Move a range in a vector to a different position.
+// The parameters are given according to the usual STL-semantics:
+//	v: a container with STL-like random access iterator via std::begin(...)
+//	rangeBegin: index of first element
+//	rangeEnd: index one *past* last element
+//	destination: index to element before which the range will be moved
+// Owing to std::begin() magic, this function works with STL-like containers:
+//	QVector<int> v{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+//	move_in_range(v, 1, 4, 6);
+// as well as with C-style arrays:
+//	int array[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+//	move_in_range(array, 1, 4, 6);
+// Both calls will have the following effect:
+//	Before: 0 1 2 3 4 5 6 7 8 9
+//	After:  0 4 5 1 2 3 6 7 8 9
+// No sanitizing of the input arguments is performed.
+template <typename Range>
+void move_in_range(Range &v, int rangeBegin, int rangeEnd, int destination)
+{
+	auto it = std::begin(v);
+	if (destination > rangeEnd)
+		std::rotate(it + rangeBegin, it + rangeEnd, it + destination);
+	else if (destination < rangeBegin)
+		std::rotate(it + destination, it + rangeBegin, it + rangeEnd);
+}
+
+#endif