nnoremap j :call CheckJ()<cr>
nnoremap k :call CheckK()<cr>
nnoremap h :call CheckH()<cr>
nnoremap l :call CheckL()<cr>

fun! CheckJ()
   if line('.') == line('$')
      norm! gg
   else
      norm! j
   endif
endfun

fun! CheckK()
   if line('.') == 1
      norm! G
   else
      norm! k
   endif
endfun

fun! CheckH()
   if col('.') == 1
      norm! $
   else
      norm! h
   endif
endfun

fun! CheckL()
   if col('.') == (col('$') - 1)
      norm! 0
   else
      norm! l
   endif
endfun