feat(furvm): introduce global variables

Closes: #59

furvm/src/executor.cpp

@@ -326,6 +326,12 @@ void executor::step() {
     case instruction_t::Store: {
         store_thing(instr.arg.u16, std::move(pop_thing()));
     } break;
+    case instruction_t::LoadGlobal: {
+        push_thing(make_reference(frame.mod->load_global_variable(instr.arg.u16)));
+    } break;
+    case instruction_t::StoreGlobal: {
+        frame.mod->store_global_variable(instr.arg.u16, std::move(pop_thing()));
+    } break;
     case instruction_t::Call: {
         push_frame(frame.mod, *frame.mod->function_at(instr.arg.u16));
     } break;

furvm/src/instruction.cpp

@@ -27,6 +27,8 @@ const std::size_t instruction_argument::s_sizes[instruction_argument::Count] = {
     4,
     // Variable:
     2,
+    // GlobalVariable:
+    2,
     // Function:
     4,
     // Offset:
@@ -54,6 +56,8 @@ const bool instruction_argument::s_signedness[instruction_argument::Count] = {
     false,
     // Variable:
     false,
+    // GlobalVariable:
+    false,
     // Function:
     false,
     // Offset:
@@ -125,6 +129,10 @@ const instruction_argument_t instruction::s_arguments[instruction::Count] = {
     instruction_argument::Variable,
     // Store:
     instruction_argument::Variable,
+    // LoadGlobal:
+    instruction_argument::GlobalVariable,
+    // StoreGlobal:
+    instruction_argument::GlobalVariable,
     // Call:
     instruction_argument::Function,
     // Jump:

furvm/src/module.cpp

@@ -88,6 +88,8 @@ std::ostream& mod::serialize(std::ostream& os) const {
         }
     }
 
+    detail::serialize(os, static_cast<std::uint16_t>(m_globalVariables.size()));
+
     detail::serialize(os, std::uint64_t(m_bytecode.size()));
     return os.write(reinterpret_cast<const char*>(m_bytecode.data()), static_cast<std::streamsize>(m_bytecode.size()));
 }
@@ -197,6 +199,10 @@ mod mod::load(std::istream& is) {
         }
     }
 
+    std::uint16_t globalVariables = 0;
+    detail::load(is, globalVariables);
+    mod.set_global_variable_count(globalVariables);
+
     std::uint64_t bytecodeLength = 0;
     detail::load(is, bytecodeLength);
     mod.bytecode().resize(bytecodeLength);