vimでsequential-command.el の <C-a> <C-e>の機能を実現したい。

"ローテート {{{
function! s:save_pos()
    let b:cur_pos = getpos('.')
endfunction
autocmd WinEnter,BufRead * call <SID>save_pos()

nnoremap h h:<C-u>call <SID>save_pos()<CR>
nnoremap j j:<C-u>call <SID>save_pos()<CR>
nnoremap k k:<C-u>call <SID>save_pos()<CR>
nnoremap l l:<C-u>call <SID>save_pos()<CR>
nnoremap b b:<C-u>call <SID>save_pos()<CR>
nnoremap <C-b> <C-b>:<C-u>call <SID>save_pos()<CR>
nnoremap <C-f> <C-f>:<C-u>call <SID>save_pos()<CR>

function! s:rotate_in_buffer(r)
    let pos_f= getpos('.')
    if pos_f == [b:cur_pos[0],1,1,b:cur_pos[0]]
        call setpos('.',b:cur_pos)
        return
    endif

    execute a:r ? "normal! ^" : "normal! $"

    let pos_s= getpos('.')

    if pos_f == pos_s
        execute a:r ? "normal! 0" : "normal! G$"
        let pos_t = getpos('.')
        if pos_s == pos_t
            if a:r
                execute "normal! gg^"
            else
                call setpos('.',b:cur_pos)
            endif
        endif
    elseif a:r && pos_s[1] == b:cur_pos[1] && pos_f[2] < pos_s[2]
        execute "normal! gg^"
    endif
endfunction

nnoremap <silent><C-a> :<C-u>call <SID>rotate_in_buffer(1)<CR>
nnoremap <silent><C-e> :<C-u>call <SID>rotate_in_buffer(0)<CR>

"}}}