Function merge_recurse 

unsafe fn merge_recurse<T, F>(
    v: *mut T,
    buf: *mut T,
    chunks: &[(usize, usize)],
    into_buf: bool,
    is_less: &F,
)
where
    T: Send,
    F: Fn(&T, &T) -> bool + Sync,

Recursively merges pre-sorted chunks inside v.

Chunks of v are stored in chunks as intervals (inclusive left and exclusive right bound). Argument buf is an auxiliary buffer that will be used during the procedure. If into_buf is true, the result will be stored into buf, otherwise it will be in v.

Safety

The number of chunks must be positive and they must be adjacent: the right bound of each chunk must equal the left bound of the following chunk.

The buffer must be at least as long as v.