feat(furvm): add step function to executor

furvm/src/executor.cpp

@@ -1,6 +1,10 @@
 #include "furvm/executor.hpp"
 
 #include "furvm/context.hpp" // IWYU pragma: keep
+#include "furvm/instruction.hpp"
+#include "furvm/thing.hpp"
+
+#include <stdexcept>
 
 namespace furvm {
 
@@ -47,4 +51,32 @@ thing_p executor::thing() const {
     return m_stack.top();
 }
 
+void executor::step() {
+    if ((m_flags & executor_flags::Suspended) == executor_flags::Suspended) return;
+
+    struct frame& frame = m_frames.top();
+
+    instruction_t instr = static_cast<instruction_t>(frame.mod->byte(frame.position++));
+    switch (instr) {
+    case instruction_t::NoOperation: break;
+    case instruction_t::Return: {
+        pop_frame();
+        if (m_frames.empty()) m_flags = m_flags | executor_flags::Done;
+    } break;
+    case instruction_t::PushB2I: {
+        auto thing     = thing::create(m_context, thing_t::Int32);
+        thing->int32() = frame.mod->byte(frame.position++);
+        m_stack.push(std::move(thing));
+    } break;
+    case instruction_t::Drop: {
+        m_stack.pop();
+    } break;
+    case instruction_t::PushConstant:
+    case instruction_t::Duplicate:
+    case instruction_t::ReturnValue: {
+        throw std::runtime_error("unimplemented");
+    }
+    }
+}
+
 } // namespace furvm

furvm/src/main.cpp

@@ -22,6 +22,10 @@ int main(void) {
     auto executor = furvm::executor::create(context);
     executor->push_frame(mainModule, 0);
 
+    while ((executor->flags() & furvm::executor_flags::Done) != furvm::executor_flags::Done) {
+        executor->step();
+    }
+
     return 0;
 }
 

furvm/src/thing.cpp

@@ -10,7 +10,7 @@ namespace furvm {
 
 std::size_t thing_type_size(thing_t type) {
     switch (type) {
-    case thing_t::Int: return 4;
+    case thing_t::Int32: return 4;
     }
     return 0;
 }
@@ -28,6 +28,16 @@ thing_p thing::create(const context_p& context, thing_t type) {
     return std::move(th);
 }
 
+std::int32_t& thing::int32() {
+    if (m_type != thing_t::Int32) throw bad_thing_access();
+    return *static_cast<std::int32_t*>(m_data);
+}
+
+const std::int32_t& thing::int32() const {
+    if (m_type != thing_t::Int32) throw bad_thing_access();
+    return *static_cast<std::int32_t*>(m_data);
+}
+
 } // namespace furvm
 
 // NOLINTEND(cppcoreguidelines-no-malloc)