fix bullets-vim#100 to correctly mark parent checkbox

Code is commented since the math is a bit tricky and not intuitive. And
vimscript doesn't like floating point calculations

plugin/bullets.vim

@@ -1238,9 +1238,22 @@ fun! s:sibling_checkbox_status(lnum)
  endif
  endif
  endfor
- let l:divisions = len(l:checkbox_markers) - 1.0
- let l:completion = float2nr(ceil(l:divisions * l:checked / l:num_siblings))
- return l:checkbox_markers[l:completion]
+ " we are interested in the number of markings that can give us sets of
+ " percentage to group the markings
+ let l:divisions = len(l:checkbox_markers) - 2.0
+ " Border case no need to calculate and it fixex the problem of the
+ " calculation below never being able to get this last number.
+ if l:checked ==# l:num_siblings
+ return l:checkbox_markers[len(l:checkbox_markers) - 1]
+ else
+ " 1.0 multiplication is to have float calculations.
+ " The calculation looks for a multiple of a percentage class to define
+ " which marker to use.
+ let l:ratio_checked = 1.0 * l:checked / l:num_siblings
+ let l:persentage_class = 1.0 / l:divisions
+ let l:completion = float2nr(ceil(l:ratio_checked / l:persentage_class))
+ return l:checkbox_markers[l:completion]
+ endif
 endfun
 
 fun! s:replace_char_in_line(lnum, chari, item)