Add ret function

bin/example.wasm

@@ -89,6 +89,11 @@ seti %B $4;
 int $3;
 
 # Jump over the interrupt
-call program_exit;
+call noop_function;
 int $3;
-program_exit:
+jmp the_real_exit;
+
+noop_function:
+ret;
+
+the_real_exit:

include/interpret/statement.hpp

@@ -66,6 +66,11 @@ namespace Interpret
 		FunctionCallStatement(std::string const & label);
 	};
 
+	struct ReturnFromFunctionStatement : Statement
+	{
+		void Execute(Execute::Flags & flags, Execute::State & state, Execute::Registers & registers) override;
+	};
+
 	struct SetStatement : Statement
 	{
 		Value firstArgument;

include/token/operandtype.hpp

@@ -14,6 +14,7 @@ namespace Token
 		ShiftIntegerRight,
 		Jump,
 		CallFunction,
+		ReturnFromFunction,
 		LessThanInteger,
 		GreaterThanInteger,
 		EqualInteger,

src/interpret/operanddefinitions.cpp

@@ -165,6 +165,11 @@ namespace Interpret
 				return std::make_unique<FunctionCallStatement>(std::get<std::string>(labelToken.data));
 			}
 
+			case Token::OperandType::ReturnFromFunction:
+			{
+				return std::make_unique<ReturnFromFunctionStatement>();
+			}
+
 			case Token::OperandType::LessThanInteger:
 			{
 				auto statement = std::make_unique<ControlFlowStatement>();
@@ -310,6 +315,7 @@ namespace Interpret
 
 			default:
 			std::printf("WARNING: returning default argument length of 0 for operand type %i\n", static_cast<int>(type));
+			case Token::OperandType::ReturnFromFunction:
 			return 0;
 		}
 	}

src/interpret/statement.cpp

@@ -66,6 +66,17 @@ namespace Interpret
 	{
 	}
 
+	void ReturnFromFunctionStatement::Execute(Execute::Flags & flags, Execute::State & state, Execute::Registers & registers)
+	{
+		if (state.stackPointer < sizeof(unsigned))
+		{
+			throw Execute::StackUnderflow();
+		}
+
+		state.nextStatement = *(reinterpret_cast<unsigned const *>(state.memory.data() + (state.stackPointer - 1u)));
+		state.stackPointer -= sizeof(unsigned);
+	}
+
 	void SetStatement::Execute(Execute::Flags & flags, Execute::State & state, Execute::Registers & registers)
 	{
 		firstArgument.GetValue(state, registers) = secondArgument.GetValue(state, registers);

src/token/operandtype.cpp

@@ -15,6 +15,7 @@ namespace Token
 			{ "shli", OperandType::ShiftIntegerLeft },
 			{ "jmp", OperandType::Jump },
 			{ "call", OperandType::CallFunction },
+			{ "ret", OperandType::ReturnFromFunction },
 			{ "lti", OperandType::LessThanInteger },
 			{ "gti", OperandType::GreaterThanInteger },
 			{ "eqi", OperandType::EqualInteger },