Simple Vim function to block comment multiple lines of code

BlockComment.vim

" Block comment multiple lines of code.
" Intended for Visual mode only
function! BlockComment(tn, bn)
  let l:ltop = line("'<")
  let l:lbottom = line("'>")
  let l:indc = indent(l:ltop)
  let l:ind = ''
  let l:i = 0
  while l:i < l:indc
    let l:ind .= ' '
    let l:i = l:i + 1
  endwhile
  call append(l:ltop-1, l:ind . a:tn)
  call append(l:lbottom+1, l:ind . a:bn)
endfunction

" The following mapping can be used to block comment multiple lines of C/C++/Java/JS code
vnoremap <silent> <leader>' :<C-u>call BlockComment('/*', '*/')<CR>