cxxrtl: add simple black box support.

This commit adds support for replacing RTLIL modules with CXXRTL
black boxes. Black box port widths may not depend on the parameters
with which it is instantiated (yet); the parameters may only be used
to change the behavior of the black box.

backends/cxxrtl/cxxrtl.h

@@ -28,7 +28,9 @@
 #include <type_traits>
 #include <tuple>
 #include <vector>
+#include <map>
 #include <algorithm>
+#include <memory>
 #include <sstream>
 
 // The cxxrtl support library implements compile time specialized arbitrary width arithmetics, as well as provides
@@ -657,6 +659,57 @@ struct memory {
 	}
 };
 
+struct parameter {
+	const enum {
+		MISSING = 0,
+		UINT   	= 1,
+		SINT   	= 2,
+		STRING 	= 3,
+		DOUBLE 	= 4,
+	} value_type;
+
+	// In debug mode, using the wrong .as_*() function will assert.
+	// In release mode, using the wrong .as_*() function will safely return a default value.
+	union {
+		const unsigned  uint_value = 0;
+		const signed    sint_value;
+	};
+	const std::string string_value = "";
+	const double      double_value = 0.0;
+
+	parameter() : value_type(MISSING) {}
+	parameter(unsigned value) : value_type(UINT), uint_value(value) {}
+	parameter(signed value) : value_type(SINT), sint_value(value) {}
+	parameter(const std::string &value) : value_type(STRING), string_value(value) {}
+	parameter(const char *value) : value_type(STRING), string_value(value) {}
+	parameter(double value) : value_type(DOUBLE), double_value(value) {}
+
+	parameter(const parameter &) = default;
+	parameter &operator=(const parameter &) = delete;
+
+	unsigned as_uint() const {
+		assert(value_type == UINT);
+		return uint_value;
+	}
+
+	signed as_sint() const {
+		assert(value_type == SINT);
+		return sint_value;
+	}
+
+	const std::string &as_string() const {
+		assert(value_type == STRING);
+		return string_value;
+	}
+
+	double as_double() const {
+		assert(value_type == DOUBLE);
+		return double_value;
+	}
+};
+
+typedef std::map<std::string, parameter> parameter_map;
+
 struct module {
 	module() {}
 	virtual ~module() {}