Function indexing::algorithms::merge_internal_indices

pub fn merge_internal_indices<T: Ord>(data: &mut [T],
                                      left_end: usize,
                                      buffer: &mut [T])

Merge internal: Merge inside data while using buffer as a swap space

data is in two sections, each part in sorted order, divided by left_end.

Merge the left and right half of data in place, while using buffer for swap space.

This is panic safe by ensuring all values are swapped and not duplicated, so it is all present in either data or buffer at all times.