From 5494ff5803623fc64683084a1de19e0e1704b4e3 Mon Sep 17 00:00:00 2001
From: "J. Hinchliffe" <jjh413@student.bham.ac.uk>
Date: Sun, 15 Jun 2025 05:03:25 +0100
Subject: [PATCH] common: start writing encoding routines (todo!)

---
 src/common/instructions.rs | 91 +++++++++++++++++++++-----------------
 1 file changed, 51 insertions(+), 40 deletions(-)

diff --git a/src/common/instructions.rs b/src/common/instructions.rs
index b66a650..da30c15 100644
--- a/src/common/instructions.rs
+++ b/src/common/instructions.rs
@@ -154,6 +154,8 @@ impl std::fmt::Display for Register {
     }
 }
 
+/// TODO: Turn argument tuples into simple structs like `TwoReg`, `TwoRegAndOff`
+/// etc just to make code a little cleaner.
 #[derive(Debug, Clone, Copy)]
 #[repr(u8)]
 pub enum Instruction {
@@ -212,6 +214,7 @@ pub enum Instruction {
     Halt = 0x24,
 }
 
+#[expect(clippy::missing_const_for_fn)]
 impl Instruction {
     /// Returns the opcode of an instruction.
     ///
@@ -226,48 +229,56 @@ impl Instruction {
     #[must_use]
     #[allow(unused)]
     pub fn encode(&self) -> u32 {
-        match self {
-            Self::Nop => todo!(),
-            Self::Mov(src, dst) => todo!(),
-            Self::MovSigned(register, register1) => todo!(),
-            Self::LoadByte(register, _, register1) => todo!(),
-            Self::LoadByteSigned(register, _, register1) => todo!(),
-            Self::LoadHalfword(register, _, register1) => todo!(),
-            Self::LoadHalfwordSigned(register, _, register1) => todo!(),
-            Self::LoadWord(register, _, register1) => todo!(),
-            Self::StoreByte(register, _, register1) => todo!(),
-            Self::StoreHalfword(register, _, register1) => todo!(),
-            Self::StoreWord(register, _, register1) => todo!(),
-            Self::LoadLowerImmediate(register, _) => todo!(),
-            Self::LoadUpperImmediate(register, _) => todo!(),
-            Self::Jump(register, _) => todo!(),
-            Self::JumpEq(register, _) => todo!(),
-            Self::JumpNeq(register, _) => todo!(),
-            Self::JumpGt(register, _) => todo!(),
-            Self::JumpGe(register, _) => todo!(),
-            Self::JumpLt(register, _) => todo!(),
-            Self::JumpLe(register, _) => todo!(),
-            Self::Compare(register, register1) => todo!(),
-            Self::Add(register, register1, register2) => todo!(),
-            Self::Sub(register, register1, register2) => todo!(),
-            Self::Increment(register) => todo!(),
-            Self::Decrement(register) => todo!(),
-            Self::ShiftLeft(register, register1, _) => todo!(),
-            Self::ShiftRight(register, register1, _) => todo!(),
-            Self::And(register, register1, register2) => todo!(),
-            Self::Or(register, register1, register2) => todo!(),
-            Self::Not(register, register1) => todo!(),
-            Self::Xor(register, register1, register2) => todo!(),
-            Self::Nand(register, register1, register2) => todo!(),
-            Self::Nor(register, register1, register2) => todo!(),
-            Self::Xnor(register, register1, register2) => todo!(),
-            Self::Interrupt(interrupt) => todo!(),
-            Self::IntReturn => todo!(),
-            Self::Halt => todo!(),
-        }
+        // match self {
+        //     _ => todo!(),
+        // }
+
+        // Note to Harry, I will finish this encode/decode shit in a few hours.
+
+        21
     }
 
-    const fn _encode_mov() {}
+    /// Encodes an R-type instruction from its fields. These must have unused high-order
+    /// bits set to 0 else the bit shifting logic is fucked.
+    ///
+    /// # Arguments
+    ///
+    /// - `shamt`: The amount to shift value (used only in shift instructions, otherwise 0).
+    #[must_use]
+    pub const fn encode_r_type(opcode: u8, sr1: u8, sr2: u8, dr: u8, shamt: u8) -> u32 {
+        let opcode = opcode as u32;
+        let sr1 = sr1 as u32;
+        let sr2 = sr2 as u32;
+        let dr = dr as u32;
+        let shamt = shamt as u32;
+
+        (opcode << 26) | (sr1 << 21) | (sr2 << 16) | (dr << 11) | (shamt << 6)
+    }
+
+    /// Encodes an I-type instruction from its fields. These must have some unused high-order
+    /// bits set to 0 else the bit shifting logic gets fucked.
+    #[must_use]
+    pub const fn encode_i_type(opcode: u8, sr1: u8, dr: u8, immediate: u16) -> u32 {
+        let opcode = opcode as u32;
+        let sr1 = sr1 as u32;
+        let dr = dr as u32;
+        let immediate = immediate as u32;
+
+        (opcode << 26) | (sr1 << 21) | (dr << 16) | immediate
+    }
+
+    #[must_use]
+    #[deprecated = "I am a little confused as to whether we keep these around for jumps."]
+    /// Encodes a J-type instruction from its fields. These must have some unused high-order
+    /// bits set to 0 else the bit shifting logic gets fucked.
+    ///
+    /// Note: the address argument is passed as-is, caller is responsible for resolving this
+    /// address properly.
+    pub const fn _encode_j_type(opcode: u8, addr: u32) -> u32 {
+        let opcode = opcode as u32;
+
+        (opcode << 26) | addr
+    }
 
     #[must_use]
     pub const fn decode(_data: u32) -> Self {