From 536969427154f8ffc71e3dd515af3bf85e43a50e Mon Sep 17 00:00:00 2001
From: iris <iris.kaizen@pm.me>
Date: Tue, 18 Aug 2026 11:30:28 +0200
Subject: [PATCH] start implementing instructions

---
 backend/src/core/cpu.rs                      |  3 +-
 backend/src/core/interpreter.rs              | 29 ++++++++--------
 backend/src/core/interpreter/decode.rs       | 36 ++++++++++++++++++++
 backend/src/core/interpreter/instructions.rs | 34 ++++++++++++++++++
 utils/src/instruction.rs                     |  6 ++--
 5 files changed, 90 insertions(+), 18 deletions(-)
 create mode 100644 backend/src/core/interpreter/decode.rs
 create mode 100644 backend/src/core/interpreter/instructions.rs

diff --git a/backend/src/core/cpu.rs b/backend/src/core/cpu.rs
index 3ddcc1b..f8021fe 100644
--- a/backend/src/core/cpu.rs
+++ b/backend/src/core/cpu.rs
@@ -8,6 +8,7 @@ pub enum CpuType {
 }
 
 pub trait Cpu {
+    fn new() -> Self;
     fn get_type() -> CpuType;
     fn get_regs(&mut self) -> &mut Registers;
     fn fetch(&self, _: &Memory, _: u64) -> Option<Instruction> {
@@ -21,7 +22,7 @@ pub trait Cpu {
     fn advance(&mut self) -> bool {
         false
     }
-    fn decode_execute(&mut self, instr: Instruction) -> Result<(), Error>;
+
     fn reset(&mut self);
     fn should_service_interrupt(&self) -> bool;
     fn update_compare_interrupt(&mut self);
diff --git a/backend/src/core/interpreter.rs b/backend/src/core/interpreter.rs
index edf5cfe..536cc31 100644
--- a/backend/src/core/interpreter.rs
+++ b/backend/src/core/interpreter.rs
@@ -3,10 +3,10 @@ use crate::core::{
     mem::Memory,
     registers::Registers,
 };
-use utils::{
-    error::{Error, Severity, Type::UnhandledInstruction},
-    instruction::Instruction,
-};
+use utils::{error::Error, instruction::Instruction};
+
+pub mod decode;
+pub mod instructions;
 
 pub struct Interpreter {
     regs: Registers,
@@ -15,6 +15,14 @@ pub struct Interpreter {
 }
 
 impl Cpu for Interpreter {
+    fn new() -> Self {
+        Self {
+            regs: Registers::new(),
+            delay_slot: false,
+            prev_delay_slot: false,
+        }
+    }
+
     fn get_type() -> super::cpu::CpuType {
         Interpreter
     }
@@ -65,16 +73,9 @@ impl Cpu for Interpreter {
         Ok(1)
     }
 
-    fn decode_execute(&mut self, instr: Instruction) -> Result<(), Error> {
-        match instr.opcode() {
-            _ => Err(Error {
-                severity: Severity::Error,
-                err_type: UnhandledInstruction(instr),
-            }),
-        }
-    }
-
     fn reset(&mut self) {
-        todo!("reset")
+        self.regs = Registers::new();
+        self.delay_slot = false;
+        self.prev_delay_slot = false;
     }
 }
diff --git a/backend/src/core/interpreter/decode.rs b/backend/src/core/interpreter/decode.rs
new file mode 100644
index 0000000..88990d3
--- /dev/null
+++ b/backend/src/core/interpreter/decode.rs
@@ -0,0 +1,36 @@
+use utils::{
+    error::{Error, Severity, Type::UnhandledInstruction},
+    instruction::Instruction,
+};
+
+use crate::core::interpreter::Interpreter;
+
+impl Interpreter {
+    pub fn decode_special(&mut self, instr: Instruction) -> Result<(), Error> {
+        match instr.special() {
+            Instruction::SLL => {
+                if instr.0 == 0 {
+                    Ok(()) // nop
+                } else {
+                    Ok(self.sll(instr))
+                }
+            }
+            Instruction::ADD => Ok(self.add(instr)),
+            Instruction::ADDU => Ok(self.addu(instr)),
+            _ => Err(Error {
+                severity: Severity::Fatal,
+                err_type: UnhandledInstruction(instr),
+            }),
+        }
+    }
+
+    pub fn decode_execute(&mut self, instr: Instruction) -> Result<(), Error> {
+        match instr.opcode() {
+            Instruction::SPECIAL => self.decode_special(instr),
+            _ => Err(Error {
+                severity: Severity::Error,
+                err_type: UnhandledInstruction(instr),
+            }),
+        }
+    }
+}
diff --git a/backend/src/core/interpreter/instructions.rs b/backend/src/core/interpreter/instructions.rs
new file mode 100644
index 0000000..df4659e
--- /dev/null
+++ b/backend/src/core/interpreter/instructions.rs
@@ -0,0 +1,34 @@
+#![allow(dead_code)]
+#![allow(unused)]
+
+use utils::{
+    error::{Error, Severity, Type::UnhandledInstruction},
+    instruction::Instruction,
+};
+
+use crate::core::interpreter::Interpreter;
+
+impl Interpreter {
+    pub fn add(&mut self, instr: Instruction) {
+        let rs = self.regs.read::<i64>(instr.rs()) as u32;
+        let rt = self.regs.read::<i64>(instr.rt()) as u32;
+        let (rd, overflow) = rs.overflowing_add(rt);
+        if overflow {
+            todo!("add overflow!")
+        }
+
+        self.regs.write(instr.rd(), rd as i32);
+    }
+
+    pub fn addu(&mut self, instr: Instruction) {
+        let rs = self.regs.read::<i64>(instr.rs()) as i32;
+        let rt = self.regs.read::<i64>(instr.rt()) as i32;
+        let rd = rs + rt;
+        self.regs.write(instr.rd(), rd);
+    }
+
+    pub fn sll(&mut self, instr: Instruction) {
+        let rd = self.regs.read::<i64>(instr.rt()) << instr.sa();
+        self.regs.write(instr.rd(), rd);
+    }
+}
diff --git a/utils/src/instruction.rs b/utils/src/instruction.rs
index dea63d6..6f05e68 100644
--- a/utils/src/instruction.rs
+++ b/utils/src/instruction.rs
@@ -5,16 +5,16 @@ bitfield! {
     pub struct Instruction(pub u32): FromStorage, IntoStorage, DerefStorage {
         pub special: u8 @ 0..6,
         pub regimm: u8 @ 16..21,
-        pub rt: u8 @ 16..21,
+        pub rt: usize @ 16..21,
         pub cop_rt: u8 @ 16..21,
-        pub rs: u8 @ 21..26,
+        pub rs: usize @ 21..26,
         pub cop_rs: u8 @ 21..26,
         pub opcode: u8 @ 26..32,
         pub imm: u16 @ 0..16,
         pub target: u32 @ 0..26,
         pub funct: u8 @ 0..6,
         pub sa: u8 @ 6..11,
-        pub rd: u8 @ 11..16,
+        pub rd: usize @ 11..16,
     }
 }