move function to autoload dir

autoload/buf_utils.vim

@@ -0,0 +1,26 @@
+function! buf_utils#GoToBuffer(count, direction) abort
+  if a:count == 0
+    if a:direction ==# 'forward'
+      bnext
+    elseif a:direction ==# 'backward'
+      bprevious
+    else
+      echoerr 'Bad argument ' a:direction
+    endif
+    return
+  endif
+  " Check the validity of buffer number.
+  if index(s:GetBufNums(), a:count) == -1
+    echohl WarningMsg | echomsg 'Invalid bufnr: ' a:count | echohl None
+    return
+  endif
+
+  " Do not use {count} for gB (it is less useful)
+  if a:direction ==# 'forward'
+    silent execute('buffer' . a:count)
+  endif
+endfunction
+
+function! s:GetBufNums() abort
+  return map(copy(getbufinfo({'buflisted':1})), 'v:val.bufnr')
+endfunction