anchor.diff:  pack_int_(N) ->
       << 16#D3:8, N:64/big-signed-integer-unit:1 >>.
   
  +-spec pack_double(float()) -> binary().
   % float : erlang's float is always IEEE 754 64bit format.
   % pack_float(F) when is_float(F)->
   %    << 16#CA:8, F:32/big-float-unit:1 >>.
  
positive.code: pack_double(F) ->
      << 16#CB:8, F:64/big-float-unit:1 >>.
  
  % raw bytes
  pack_raw(Bin) ->
      case byte_size(Bin) of
  
negative.code: pack_uint_(N) ->
      << 16#CF:8, N:64/big-unsigned-integer-unit:1 >>.
  
  -spec pack_int_(integer()) -> binary().
  % negative fixnum
  pack_int_(N) when N >= -32->
      << 2#111:3, N:5 >>;
  