feat: Support multiplexed signals

Parse the optional multiplexer indicator on SG_ lines (M, mN and mNM).
Previously these lines did not match the signal regex and were silently
dropped.

- Signal gains is_multiplexor and multiplexer_value; is_multiplexed is
  now set from the parsed indicator.
- Decoding reads the multiplexor's raw value and only emits the
  non multiplexed signals plus those matching that value.
- New parse_signals / parse_message overloads return values keyed by
  signal name, since positional output is ambiguous for multiplexed
  messages.

Extended multiplexing (SG_MUL_VAL_) is not supported yet: mNM signals
are parsed, but all multiplexed signals are switched by the top level
multiplexor.

Author: MCFurry

include/libdbc/dbc.hpp

@@ -6,6 +6,7 @@
 #include <libdbc/message.hpp>
 #include <regex>
 #include <string>
+#include <unordered_map>
 #include <vector>
 
 namespace Libdbc {
@@ -32,6 +33,7 @@ class DbcParser : public Parser {
 	std::vector<Libdbc::Message> get_messages() const;
 
 	Message::ParseSignalsStatus parse_message(uint32_t message_id, const std::vector<uint8_t>& data, std::vector<double>& out_values);
+	Message::ParseSignalsStatus parse_message(uint32_t message_id, const std::vector<uint8_t>& data, std::unordered_map<std::string, double>& out_values);
 
 	std::vector<std::string> unused_lines() const;
 

include/libdbc/message.hpp

@@ -5,6 +5,7 @@
 #include <iostream>
 #include <libdbc/signal.hpp>
 #include <string>
+#include <unordered_map>
 #include <vector>
 
 namespace Libdbc {
@@ -21,7 +22,11 @@ struct Message {
 		ErrorInvalidConversion,
 	};
 
+	// Decodes the signals present in data, in signal order. For multiplexed messages only the multiplexor,
+	// the non multiplexed signals and the signals matching the current multiplexer value are present.
 	ParseSignalsStatus parse_signals(const std::vector<uint8_t>& data, std::vector<double>& values) const;
+	// Same as above but keyed by signal name, so multiplexed messages can be decoded without tracking which signals are present.
+	ParseSignalsStatus parse_signals(const std::vector<uint8_t>& data, std::unordered_map<std::string, double>& values) const;
 
 	void append_signal(const Signal& signal);
 	std::vector<Signal> get_signals() const;

include/libdbc/signal.hpp

@@ -15,7 +15,9 @@ struct Signal {
 	};
 
 	std::string name;
-	bool is_multiplexed;
+	bool is_multiplexed; // Signal is only present for a specific multiplexer value (mN)
+	bool is_multiplexor = false; // Signal is the multiplexer switch of its message (M)
+	uint32_t multiplexer_value = 0; // Multiplexer value this signal is present for. Only valid if is_multiplexed
 	uint32_t start_bit;
 	uint32_t size;
 	bool is_bigendian;

src/dbc.cpp

@@ -9,6 +9,7 @@
 #include <libdbc/utils/utils.hpp>
 #include <regex>
 #include <string>
+#include <unordered_map>
 #include <vector>
 
 namespace Libdbc {
@@ -17,6 +18,7 @@ const auto floatPattern = "(-?\\d+\\.?(\\d+)?)"; // Can be negative
 
 const auto signalIdentifierPattern = "(SG_)";
 const auto namePattern = "(\\w+)";
+const auto multiplexerPattern = "(?:\\s(M|m\\d+M?))?"; // Optional: M = multiplexor, mN = multiplexed by value N, mNM = both
 const auto bitStartPattern = "(\\d+)"; // Cannot be negative
 const auto lengthPattern = "(\\d+)"; // Cannot be negative
 const auto byteOrderPattern = "([0-1])";
@@ -34,16 +36,17 @@ const auto receiverPattern = "([\\w\\,]+|Vector__XXX)*";
 const auto whiteSpace = "\\s";
 
 constexpr unsigned SIGNAL_NAME_GROUP = 2;
-constexpr unsigned SIGNAL_START_BIT_GROUP = 3;
-constexpr unsigned SIGNAL_SIZE_GROUP = 4;
-constexpr unsigned SIGNAL_ENDIAN_GROUP = 5;
-constexpr unsigned SIGNAL_SIGNED_GROUP = 6;
-constexpr unsigned SIGNAL_FACTOR_GROUP = 7;
-constexpr unsigned SIGNAL_OFFSET_GROUP = 9;
-constexpr unsigned SIGNAL_MIN_GROUP = 11;
-constexpr unsigned SIGNAL_MAX_GROUP = 13;
-constexpr unsigned SIGNAL_UNIT_GROUP = 15;
-constexpr unsigned SIGNAL_RECIEVER_GROUP = 16;
+constexpr unsigned SIGNAL_MULTIPLEXER_GROUP = 3;
+constexpr unsigned SIGNAL_START_BIT_GROUP = 4;
+constexpr unsigned SIGNAL_SIZE_GROUP = 5;
+constexpr unsigned SIGNAL_ENDIAN_GROUP = 6;
+constexpr unsigned SIGNAL_SIGNED_GROUP = 7;
+constexpr unsigned SIGNAL_FACTOR_GROUP = 8;
+constexpr unsigned SIGNAL_OFFSET_GROUP = 10;
+constexpr unsigned SIGNAL_MIN_GROUP = 12;
+constexpr unsigned SIGNAL_MAX_GROUP = 14;
+constexpr unsigned SIGNAL_UNIT_GROUP = 16;
+constexpr unsigned SIGNAL_RECIEVER_GROUP = 17;
 
 constexpr unsigned MESSAGE_ID_GROUP = 2;
 constexpr unsigned MESSAGE_NAME_GROUP = 3;
@@ -63,11 +66,9 @@ DbcParser::DbcParser()
 	, node_re("^(BU_:)\\s?((?:[\\w]+?\\s?)*)?")
 	, message_re("^(BO_)\\s(\\d+)\\s(\\w+)\\:\\s(\\d+)\\s(\\w+|Vector__XXX)")
 	, value_re("^(VAL_)\\s(\\d+)\\s(\\w+)((?:\\s(\\d+)\\s\"([^\"]*)\")+)\\s;$")
-	,
-	// NOTE: No multiplex support yet
-	signal_re(std::string("^") + whiteSpace + signalIdentifierPattern + whiteSpace + namePattern + whiteSpace + "\\:" + whiteSpace + bitStartPattern + "\\|"
-			  + lengthPattern + "\\@" + byteOrderPattern + signPattern + whiteSpace + offsetScalePattern + whiteSpace + minMaxPattern + whiteSpace + unitPattern
-			  + whiteSpace + receiverPattern) {
+	, signal_re(std::string("^") + whiteSpace + signalIdentifierPattern + whiteSpace + namePattern + multiplexerPattern + whiteSpace + "\\:" + whiteSpace
+				+ bitStartPattern + "\\|" + lengthPattern + "\\@" + byteOrderPattern + signPattern + whiteSpace + offsetScalePattern + whiteSpace
+				+ minMaxPattern + whiteSpace + unitPattern + whiteSpace + receiverPattern) {
 }
 
 void DbcParser::parse_file(std::istream& stream) {
@@ -128,6 +129,16 @@ Message::ParseSignalsStatus DbcParser::parse_message(const uint32_t message_id,
 	return Message::ParseSignalsStatus::ErrorUnknownID;
 }
 
+Message::ParseSignalsStatus
+DbcParser::parse_message(const uint32_t message_id, const std::vector<uint8_t>& data, std::unordered_map<std::string, double>& out_values) {
+	for (const auto& message : messages) {
+		if (message.id() == message_id) {
+			return message.parse_signals(data, out_values);
+		}
+	}
+	return Message::ParseSignalsStatus::ErrorUnknownID;
+}
+
 void DbcParser::parse_dbc_header(std::istream& file_stream) {
 	std::string line;
 	std::smatch match;
@@ -183,7 +194,11 @@ void DbcParser::parse_dbc_messages(const std::vector<std::string>& lines) {
 
 		if (std::regex_search(line, match, signal_re) && !messages.empty()) {
 			std::string name = match.str(SIGNAL_NAME_GROUP);
-			bool is_multiplexed = false; // No support yet
+			// Multiplexer indicator: "M", "mN" or "mNM" (extended multiplexing)
+			std::string multiplexer = match.str(SIGNAL_MULTIPLEXER_GROUP);
+			bool is_multiplexed = !multiplexer.empty() && multiplexer.front() == 'm';
+			bool is_multiplexor = !multiplexer.empty() && multiplexer.back() == 'M';
+			uint32_t multiplexer_value = is_multiplexed ? static_cast<uint32_t>(std::stoul(multiplexer.substr(1))) : 0;
 			uint32_t start_bit = static_cast<uint32_t>(std::stoul(match.str(SIGNAL_START_BIT_GROUP)));
 			uint32_t size = static_cast<uint32_t>(std::stoul(match.str(SIGNAL_SIZE_GROUP)));
 			bool is_bigendian = (std::stoul(match.str(SIGNAL_ENDIAN_GROUP)) == 0);
@@ -200,6 +215,8 @@ void DbcParser::parse_dbc_messages(const std::vector<std::string>& lines) {
 			Utils::String::split(match.str(SIGNAL_RECIEVER_GROUP), receivers, ',');
 
 			Signal sig(name, is_multiplexed, start_bit, size, is_bigendian, is_signed, factor, offset, min, max, unit, receivers);
+			sig.is_multiplexor = is_multiplexor;
+			sig.multiplexer_value = multiplexer_value;
 			messages.back().append_signal(sig);
 			continue;
 		}

src/message.cpp

@@ -4,6 +4,7 @@
 #include <libdbc/signal.hpp>
 #include <ostream>
 #include <string>
+#include <unordered_map>
 #include <vector>
 
 namespace Libdbc {
@@ -26,10 +27,55 @@ bool Message::operator==(const Message& rhs) const {
 	return (m_id == rhs.id()) && (m_name == rhs.m_name) && (m_size == rhs.m_size) && (m_node == rhs.m_node);
 }
 
-Message::ParseSignalsStatus Message::parse_signals(const std::vector<uint8_t>& data, std::vector<double>& values) const {
+namespace {
+
+// Extracts the raw (unscaled) bits of a signal. Bits above signal.size are not masked off.
+uint64_t extract_raw(const Signal& signal, uint64_t data_little_endian, uint64_t data_big_endian, std::size_t len) {
+	if (signal.is_bigendian) {
+		uint32_t start_bit = ONE_BYTE * (signal.start_bit / ONE_BYTE) + (SEVEN_BITS - (signal.start_bit % ONE_BYTE)); // Calculation taken from python CAN
+		uint64_t value = data_big_endian << start_bit;
+		return value >> (len - signal.size);
+	}
+	return data_little_endian >> signal.start_bit;
+}
+
+double to_physical(const Signal& signal, uint64_t value) {
+	if (signal.is_signed && signal.size > 1) {
+		switch (signal.size) {
+		case ONE_BYTE:
+			return static_cast<int8_t>(value) * signal.factor + signal.offset;
+		case TWO_BYTES:
+			return static_cast<int16_t>(value) * signal.factor + signal.offset;
+		case FOUR_BYTES:
+			return static_cast<int32_t>(value) * signal.factor + signal.offset;
+		case EIGHT_BYTES:
+			return static_cast<double>(value) * signal.factor + signal.offset;
+		default: {
+			// 2 complement -> decimal
+			const bool is_negative = (value & (1ULL << (signal.size - 1))) != 0;
+			int64_t nativeInt = 0;
+			if (is_negative) {
+				nativeInt = static_cast<int64_t>(value | ~((1ULL << signal.size) - 1)); // invert all bits above signal.size
+			} else {
+				nativeInt = static_cast<int64_t>(value & ((1ULL << signal.size) - 1)); // masking
+			}
+			return static_cast<double>(nativeInt) * signal.factor + signal.offset;
+		}
+		}
+	}
+	// use only the relevant bits
+	value = value & ((1 << signal.size) - 1); // masking
+	return static_cast<double>(value) * signal.factor + signal.offset;
+}
+
+// Decodes every signal that is present in the frame and hands it to on_value(signal, value).
+// Multiplexed signals are only present when the multiplexor's raw value matches their multiplexer value.
+// NOTE: Extended multiplexing (SG_MUL_VAL_) is not supported. All multiplexed signals are switched by the top level multiplexor.
+template<typename OnValue>
+Message::ParseSignalsStatus decode_signals(const std::vector<Signal>& signals, const std::vector<uint8_t>& data, OnValue on_value) {
 	auto size = data.size();
 	if (size > ONE_BYTE) {
-		return ParseSignalsStatus::ErrorMessageToLong; // not supported yet
+		return Message::ParseSignalsStatus::ErrorMessageToLong; // not supported yet
 	}
 
 	uint64_t data_little_endian = 0;
@@ -42,50 +88,41 @@ Message::ParseSignalsStatus Message::parse_signals(const std::vector<uint8_t>& d
 	// TODO: does this also work on a big endian machine?
 
 	const auto len = size * 8;
-	uint64_t value = 0;
-	for (const auto& signal : m_signals) {
-		if (signal.is_bigendian) {
-			uint32_t start_bit = ONE_BYTE * (signal.start_bit / ONE_BYTE) + (SEVEN_BITS - (signal.start_bit % ONE_BYTE)); // Calculation taken from python CAN
-			value = data_big_endian << start_bit;
-			value = value >> (len - signal.size);
-		} else {
-			value = data_little_endian >> signal.start_bit;
-		}
 
-		if (signal.is_signed && signal.size > 1) {
-			switch (signal.size) {
-			case ONE_BYTE:
-				values.push_back(static_cast<int8_t>(value) * signal.factor + signal.offset);
-				break;
-			case TWO_BYTES:
-				values.push_back(static_cast<int16_t>(value) * signal.factor + signal.offset);
-				break;
-			case FOUR_BYTES:
-				values.push_back(static_cast<int32_t>(value) * signal.factor + signal.offset);
-				break;
-			case EIGHT_BYTES:
-				values.push_back(static_cast<double>(value) * signal.factor + signal.offset);
-				break;
-			default: {
-				// 2 complement -> decimal
-				const bool is_negative = (value & (1ULL << (signal.size - 1))) != 0;
-				int64_t nativeInt = 0;
-				if (is_negative) {
-					nativeInt = static_cast<int64_t>(value | ~((1ULL << signal.size) - 1)); // invert all bits above signal.size
-				} else {
-					nativeInt = static_cast<int64_t>(value & ((1ULL << signal.size) - 1)); // masking
-				}
-				values.push_back(static_cast<double>(nativeInt) * signal.factor + signal.offset);
-				break;
+	bool has_multiplexor = false;
+	uint64_t multiplexer_value = 0;
+	for (const auto& signal : signals) {
+		if (signal.is_multiplexor && !signal.is_multiplexed) {
+			multiplexer_value = extract_raw(signal, data_little_endian, data_big_endian, len);
+			if (signal.size < EIGHT_BYTES) {
+				multiplexer_value &= (1ULL << signal.size) - 1;
 			}
-			}
-		} else {
-			// use only the relevant bits
-			value = value & ((1 << signal.size) - 1); // masking
-			values.push_back(static_cast<double>(value) * signal.factor + signal.offset);
+			has_multiplexor = true;
+			break;
+		}
+	}
+
+	for (const auto& signal : signals) {
+		if (signal.is_multiplexed && (!has_multiplexor || signal.multiplexer_value != multiplexer_value)) {
+			continue;
 		}
+		on_value(signal, to_physical(signal, extract_raw(signal, data_little_endian, data_big_endian, len)));
 	}
-	return ParseSignalsStatus::Success;
+	return Message::ParseSignalsStatus::Success;
+}
+
+}
+
+Message::ParseSignalsStatus Message::parse_signals(const std::vector<uint8_t>& data, std::vector<double>& values) const {
+	return decode_signals(m_signals, data, [&values](const Signal&, double value) {
+		values.push_back(value);
+	});
+}
+
+Message::ParseSignalsStatus Message::parse_signals(const std::vector<uint8_t>& data, std::unordered_map<std::string, double>& values) const {
+	return decode_signals(m_signals, data, [&values](const Signal& signal, double value) {
+		values[signal.name] = value;
+	});
 }
 
 void Message::append_signal(const Signal& signal) {

src/signal.cpp

@@ -32,7 +32,8 @@ Signal::Signal(std::string name,
 }
 
 bool Signal::operator==(const Signal& rhs) const {
-	return (this->name == rhs.name) && (this->is_multiplexed == rhs.is_multiplexed) && (this->start_bit == rhs.start_bit) && (this->size == rhs.size)
+	return (this->name == rhs.name) && (this->is_multiplexed == rhs.is_multiplexed) && (this->is_multiplexor == rhs.is_multiplexor)
+		&& (this->multiplexer_value == rhs.multiplexer_value) && (this->start_bit == rhs.start_bit) && (this->size == rhs.size)
 		&& (this->is_bigendian == rhs.is_bigendian) && (this->is_signed == rhs.is_signed) && (this->offset == rhs.offset) && (this->min == rhs.min)
 		&& (this->max == rhs.max) && (this->unit == rhs.unit) && (this->receivers == rhs.receivers);
 }
@@ -44,6 +45,10 @@ bool Signal::operator<(const Signal& rhs) const {
 std::ostream& operator<<(std::ostream& out, const Signal& sig) {
 	out << "Signal {name: " << sig.name << ", ";
 	out << "Multiplexed: " << (sig.is_multiplexed ? "True" : "False") << ", ";
+	if (sig.is_multiplexed) {
+		out << "Multiplexer value: " << sig.multiplexer_value << ", ";
+	}
+	out << "Multiplexor: " << (sig.is_multiplexor ? "True" : "False") << ", ";
 	out << "Start bit: " << sig.start_bit << ", ";
 	out << "Size: " << sig.size << ", ";
 	out << "Endianness: " << (sig.is_bigendian ? "Big endian" : "Little endian") << ", ";