更优雅,更简单的方法将代码转换为UTF-8

对于 this question,我创建了以下Lua代码,将Unicode代码点转换为UTF-8字符串.有没有更好的方法(在Lua 5.1中)？在这种情况下,“更好”意味着“显着提高效率,或者更优选更少的代码行”.

注意：我并不是真的要求这个算法的code review;我要求更好的算法(或内置库).

do
  local bytebits = {
    {0x7F,{0,128}},
    {0x7FF,{192,32},{128,64}},
    {0xFFFF,{224,16},{128,64},{128,64}},
    {0x1FFFFF,{240,8},{128,64},{128,64},{128,64}}
  }
  function utf8(decimal)
    local charbytes = {}
    for b,lim in ipairs(bytebits) do
      if decimal<=lim[1] then
        for i=b,1,-1 do
          local prefix,max = lim[i+1][1],lim[i+1][2]
          local mod = decimal % max
          charbytes[i] = string.char( prefix + mod )
          decimal = ( decimal - mod ) / max
        end
        break
      end
    end
    return table.concat(charbytes)
  end
end

c=utf8(0x24)     print(c.." is "..#c.." bytes.") --> $is 1 bytes.
c=utf8(0xA2)     print(c.." is "..#c.." bytes.") --> ¢ is 2 bytes.
c=utf8(0x20AC)   print(c.." is "..#c.." bytes.") --> € is 3 bytes.  
c=utf8(0xFFFF)   print(c.." is "..#c.." bytes.") -->  is 3 bytes.
c=utf8(0x10000)  print(c.." is "..#c.." bytes.") -->