Function split_slice_at_file

pub fn split_slice_at_file(
    current_row_offset_ref: &mut usize,
    n_rows_this_file: usize,
    global_slice_start: usize,
    global_slice_end: usize,
) -> (usize, usize)

Given a slice that is relative to the start of a list of files, calculate the slice to apply at a file with a row offset of current_row_offset.