feat(furvm): introduce missing push instructions

Closes: #58

furc/src/back/furvm.cpp

@@ -170,7 +170,7 @@ void furvm_generator::generate_operand(furvm::mod& mod, function_context& ctx, c
         static_assert(sizeof(var) == 2, "sizeof(furvm::variable_t) has changed");
     } break;
     case furlang::ir::operand_t::Integer: {
-        mod.bytecode().push_back(static_cast<furvm::byte>(furvm::instruction_t::PushB2I));
+        mod.bytecode().push_back(static_cast<furvm::byte>(furvm::instruction_t::PushS32));
         mod.bytecode().push_back(operand.integer());
     } break;
     case furlang::ir::operand_t::Variable:

furvm/include/furvm/instruction.hpp

@@ -12,11 +12,34 @@ enum class instruction_t : byte {
     NoOperation = 0,
 
     /**
-     * @brief Pushes an integer from a byte onto the stack.
-     *
-     * Pushes an integer constructed from a next byte onto the stack.
+     * @brief Pushes an s8 integer from a byte onto the stack.
      */
-    PushB2I,
+    PushS8,
+
+    /**
+     * @brief Pushes an u8 integer from a byte onto the stack.
+     */
+    PushU8,
+
+    /**
+     * @brief Pushes an s16 integer from two byte onto the stack.
+     */
+    PushS16,
+
+    /**
+     * @brief Pushes an u16 integer from two byte onto the stack.
+     */
+    PushU16,
+
+    /**
+     * @brief Pushes an s32 integer from a byte onto the stack.
+     */
+    PushS32,
+
+    /**
+     * @brief Pushes an u32 integer from a byte onto the stack.
+     */
+    PushU32,
 
     /**
      * @brief Pushes a constant onto the stack.

furvm/src/executor.cpp

@@ -133,9 +133,33 @@ void executor::step() {
     instruction_t instr = static_cast<instruction_t>((*frame.mod).byte(frame.position++));
     switch (instr) {
     case instruction_t::NoOperation: break;
-    case instruction_t::PushB2I: {
-        push_thing({ (struct thing_type){ thing_type::S32 }, m_context->thing_alloc() })->get<int>() =
-            frame.mod->byte(frame.position++);
+    case instruction_t::PushS8: {
+        push_thing({ (struct thing_type){ thing_type::S8 }, m_context->thing_alloc() })->get<thing_type::s8>() =
+            static_cast<thing_type::s8>(frame.mod->byte(frame.position++));
+    } break;
+    case instruction_t::PushU8: {
+        push_thing({ (struct thing_type){ thing_type::U8 }, m_context->thing_alloc() })->get<thing_type::u8>() =
+            static_cast<thing_type::u8>(frame.mod->byte(frame.position++));
+    } break;
+    case instruction_t::PushS16: {
+        thing_type::u16 value = frame.mod->byte(frame.position++);
+        value                |= static_cast<thing_type::u16>(frame.mod->byte(frame.position++) << 8);
+        push_thing({ (struct thing_type){ thing_type::S16 }, m_context->thing_alloc() })->get<thing_type::s16>() =
+            static_cast<thing_type::s16>(value);
+    } break;
+    case instruction_t::PushU16: {
+        thing_type::u16 value = frame.mod->byte(frame.position++);
+        value                |= static_cast<thing_type::u16>(frame.mod->byte(frame.position++) << 8);
+        push_thing({ (struct thing_type){ thing_type::U16 }, m_context->thing_alloc() })->get<thing_type::u16>() =
+            value;
+    } break;
+    case instruction_t::PushS32: {
+        push_thing({ (struct thing_type){ thing_type::S32 }, m_context->thing_alloc() })->get<thing_type::s32>() =
+            static_cast<thing_type::s32>(frame.mod->byte(frame.position++));
+    } break;
+    case instruction_t::PushU32: {
+        push_thing({ (struct thing_type){ thing_type::U32 }, m_context->thing_alloc() })->get<thing_type::u32>() =
+            static_cast<thing_type::u32>(frame.mod->byte(frame.position++));
     } break;
     case instruction_t::Array: {
         mod_type_id typeId = static_cast<mod_type_id>(frame.mod->byte(frame.position)) |