Potentially more efficient PB decoding

pb_decode.erl

-module(pb_decode).

-compile(export_all).

%% existing code
d_msg_rpberrorresp(Bin, TrUserData) ->
    dfp_read_field_def_rpberrorresp(Bin, 0, 0,
				    id(undefined, TrUserData),
				    id(undefined, TrUserData), TrUserData).

dfp_read_field_def_rpberrorresp(<<10, Rest/binary>>, Z1,
				Z2, F1, F2, TrUserData) ->
    d_field_rpberrorresp_errmsg(Rest, Z1, Z2, F1, F2,
				TrUserData);
dfp_read_field_def_rpberrorresp(<<16, Rest/binary>>, Z1,
				Z2, F1, F2, TrUserData) ->
    d_field_rpberrorresp_errcode(Rest, Z1, Z2, F1, F2,
				 TrUserData);
dfp_read_field_def_rpberrorresp(<<>>, 0, 0, F1, F2,
				_) ->
    #rpberrorresp{errmsg = F1, errcode = F2};
dfp_read_field_def_rpberrorresp(Other, Z1, Z2, F1, F2,
				TrUserData) ->
    dg_read_field_def_rpberrorresp(Other, Z1, Z2, F1, F2,
				   TrUserData).

dg_read_field_def_rpberrorresp(<<1:1, X:7,
				 Rest/binary>>,
			       N, Acc, F1, F2, TrUserData)
    when N < 32 - 7 ->
    dg_read_field_def_rpberrorresp(Rest, N + 7,
				   X bsl N + Acc, F1, F2, TrUserData);
dg_read_field_def_rpberrorresp(<<0:1, X:7,
				 Rest/binary>>,
			       N, Acc, F1, F2, TrUserData) ->
    Key = X bsl N + Acc,
    case Key of
      10 ->
	  d_field_rpberrorresp_errmsg(Rest, 0, 0, F1, F2,
				      TrUserData);
      16 ->
	  d_field_rpberrorresp_errcode(Rest, 0, 0, F1, F2,
				       TrUserData);
      _ ->
	  case Key band 7 of
	    0 ->
		skip_varint_rpberrorresp(Rest, 0, 0, F1, F2,
					 TrUserData);
	    1 ->
		skip_64_rpberrorresp(Rest, 0, 0, F1, F2, TrUserData);
	    2 ->
		skip_length_delimited_rpberrorresp(Rest, 0, 0, F1, F2,
						   TrUserData);
	    5 ->
		skip_32_rpberrorresp(Rest, 0, 0, F1, F2, TrUserData)
	  end
    end;
dg_read_field_def_rpberrorresp(<<>>, 0, 0, F1, F2, _) ->
    #rpberrorresp{errmsg = F1, errcode = F2}.

d_field_rpberrorresp_errmsg(<<1:1, X:7, Rest/binary>>,
			    N, Acc, F1, F2, TrUserData)
    when N < 57 ->
    d_field_rpberrorresp_errmsg(Rest, N + 7, X bsl N + Acc,
				F1, F2, TrUserData);
d_field_rpberrorresp_errmsg(<<0:1, X:7, Rest/binary>>,
			    N, Acc, _, F2, TrUserData) ->
    Len = X bsl N + Acc,
    <<Bytes:Len/binary, Rest2/binary>> = Rest,
    NewFValue = binary:copy(Bytes),
    dfp_read_field_def_rpberrorresp(Rest2, 0, 0, NewFValue,
				    F2, TrUserData).


d_field_rpberrorresp_errcode(<<1:1, X:7, Rest/binary>>,
			     N, Acc, F1, F2, TrUserData)
    when N < 57 ->
    d_field_rpberrorresp_errcode(Rest, N + 7, X bsl N + Acc,
				 F1, F2, TrUserData);
d_field_rpberrorresp_errcode(<<0:1, X:7, Rest/binary>>,
			     N, Acc, F1, _, TrUserData) ->
    NewFValue = X bsl N + Acc,
    dfp_read_field_def_rpberrorresp(Rest, 0, 0, F1,
				    NewFValue, TrUserData).


skip_varint_rpberrorresp(<<1:1, _:7, Rest/binary>>, Z1,
			 Z2, F1, F2, TrUserData) ->
    skip_varint_rpberrorresp(Rest, Z1, Z2, F1, F2,
			     TrUserData);
skip_varint_rpberrorresp(<<0:1, _:7, Rest/binary>>, Z1,
			 Z2, F1, F2, TrUserData) ->
    dfp_read_field_def_rpberrorresp(Rest, Z1, Z2, F1, F2,
				    TrUserData).


skip_length_delimited_rpberrorresp(<<1:1, X:7,
				     Rest/binary>>,
				   N, Acc, F1, F2, TrUserData)
    when N < 57 ->
    skip_length_delimited_rpberrorresp(Rest, N + 7,
				       X bsl N + Acc, F1, F2, TrUserData);
skip_length_delimited_rpberrorresp(<<0:1, X:7,
				     Rest/binary>>,
				   N, Acc, F1, F2, TrUserData) ->
    Length = X bsl N + Acc,
    <<_:Length/binary, Rest2/binary>> = Rest,
    dfp_read_field_def_rpberrorresp(Rest2, 0, 0, F1, F2,
				    TrUserData).


skip_32_rpberrorresp(<<_:32, Rest/binary>>, Z1, Z2, F1,
		     F2, TrUserData) ->
    dfp_read_field_def_rpberrorresp(Rest, Z1, Z2, F1, F2,
				    TrUserData).


skip_64_rpberrorresp(<<_:64, Rest/binary>>, Z1, Z2, F1,
		     F2, TrUserData) ->
    dfp_read_field_def_rpberrorresp(Rest, Z1, Z2, F1, F2,
				    TrUserData).


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% ideas

%% once for all bytes decoding.
%% this should be in the library, not generated every time.
%% Note: this will fail if the length of the bytes is over 2^28 :-)
%% binary_to_term fails when the binary is over 2^32 in length...


decode_bytes(Binary) ->
  {Length, Rest} = chop_encoded_integer(Binary),
  <<Bytes:Length/binary, Rest2/binary>> = Rest,
  {Bytes, Rest2}.

decode_uint32(Binary) ->
  {Length, Rest} = chop_encoded_integer(Binary),
  <<UInt32:Length, Rest2/binary>> = Rest,
  {UInt32, Rest2}.

chop_encoded_integer(<<0:1, Len:7, Rest/binary>>) ->
  {Len, Rest};
chop_encoded_integer(<<1:1, Len1:7, 0:1, Len2, Rest/binary>>) ->
  Len = Len1 * 128 + Len2,
  {Len, Rest};
chop_encoded_integer(<<1:1, Len1:7, 1:1, Len2:7, 0:1, Len3:7, Rest/binary>>) ->
  Len = Len1 * 16384 + Len2 * 128 + Len3,
  {Len, Rest};
chop_encoded_integer(<<1:1, Len1:7, 1:1, Len2:7, 1:1, Len3:7, 1:0, Len4:7, Rest/binary>>) ->
  Len = Len1 * 2097152 + Len2 * 16384 + Len3 * 128 + Len4,
  {Len, Rest}.
  


  
d_rpberrorresp(Bin, TrUserData) ->
  d_rpberrorresp_read_field(Bin, #rpberrorresp{}, TrUserData).

d_rpberrorresp_read_field(Bin, RpbErrorResp, TrUserData) ->
  {Key, Rest} = chop_encoded_integer(Bin),
  d_rpberrorresp_read_field_key(Key, Rest, RpbErrorResp, TrUserData);
d_rpberrorresp_read_field(<<>>, RpbErrorResp, _TrUserData) ->
  RpbErrorResp.

d_rpberrorresp_read_field_key(10, Rest, RpbErrorResp, TrUserData) ->
  {Bytes, Rest2} = decode_bytes(Rest),
  d_rpberrorresp_read_field(Rest2, RpbErrorResp#rpberrorresp{errmsg=Bytes}, TrUserData); 
d_rpberrorresp_read_field_key(16, Rest, RpbErrorResp, TrUserData) ->
  {UInt32, Rest2} = decode_uint32(Rest),
  d_rpberrorresp_read_field(Rest2, RpbErrorResp#rpberrorresp{errcode=UInt32});
d_rpberrorresp_read_field_key(Key, Rest, RpbErrorResp, TrUserData) ->
  case Key band 7 of
    0 ->
      skip_varint_rpberrorresp(Rest, 0, 0, F1, F2,
                               TrUserData);
    1 ->
      skip_64_rpberrorresp(Rest, 0, 0, F1, F2, TrUserData);
    2 ->
      skip_length_delimited_rpberrorresp(Rest, 0, 0, F1, F2,
                                         TrUserData);
    5 ->
      skip_32_rpberrorresp(Rest, 0, 0, F1, F2, TrUserData)
  end.