From 3372e774e9505acdc3778a8155476cca4bfbd3e8 Mon Sep 17 00:00:00 2001
From: krolxon <krolyxon@tutanota.com>
Date: Thu, 8 Jan 2026 18:47:07 +0530
Subject: [PATCH] add MUL & DIV

---
 README.md           |  2 ++
 examples/div.asm    |  4 ++++
 examples/mul.asm    |  4 ++++
 src/assembler.rs    | 21 ++++++++++++++++++++-
 src/cpu.rs          | 42 ++++++++++++++++++++++++++++++++++++++++--
 src/instructions.rs |  4 ++++
 6 files changed, 74 insertions(+), 3 deletions(-)
 create mode 100644 examples/div.asm
 create mode 100644 examples/mul.asm

diff --git a/README.md b/README.md
index 0fda2d6..fd391d2 100644
--- a/README.md
+++ b/README.md
@@ -47,6 +47,8 @@ cargo run -- --f <examples/filename.asc>
     - [x] Add label support (supporting JMP/JZ/JNZ)
 - [ ] Add instructions
     - [x] CMP
+    - [x] MUL
+    - [x] DIV
     - [ ] CALL
     - [ ] RET
 - [ ] Error handling
diff --git a/examples/div.asm b/examples/div.asm
new file mode 100644
index 0000000..f07766c
--- /dev/null
+++ b/examples/div.asm
@@ -0,0 +1,4 @@
+mov a, 10
+mov b, 2
+div a, b
+hlt
diff --git a/examples/mul.asm b/examples/mul.asm
new file mode 100644
index 0000000..a818dfd
--- /dev/null
+++ b/examples/mul.asm
@@ -0,0 +1,4 @@
+mov a, 99
+mov b, 99
+mul a, b
+hlt
diff --git a/src/assembler.rs b/src/assembler.rs
index e7aa305..1b9c85b 100644
--- a/src/assembler.rs
+++ b/src/assembler.rs
@@ -25,7 +25,7 @@ fn is_reg(s: &str) -> bool {
 
 fn instr_size(tokens: &[String]) -> u16 {
     match tokens[0].as_str() {
-        "mov" | "add" | "sub" | "jmp" | "jz" | "jnz" | "cmp" => 3,
+        "mov" | "add" | "sub" | "jmp" | "jz" | "jnz" | "cmp" | "mul" | "div" => 3,
         "hlt" => 1,
         _ => panic!("Unknown instruction {}", tokens[0]),
     }
@@ -153,6 +153,25 @@ pub fn assembler(source: &str) -> Vec<u8> {
                 }
             }
 
+            "mul" => {
+                let r1 = parse_reg(&tokens[1]);
+                let r2 = parse_reg(&tokens[2]);
+
+                bytes.push(Instruction::MUL as u8);
+                bytes.push(r1);
+                bytes.push(r2);
+
+            }
+
+            "div" => {
+                let r1 = parse_reg(&tokens[1]);
+                let r2 = parse_reg(&tokens[2]);
+
+                bytes.push(Instruction::DIV as u8);
+                bytes.push(r1);
+                bytes.push(r2);
+            }
+
             "hlt" => {
                 bytes.push(Instruction::HLT as u8);
             }
diff --git a/src/cpu.rs b/src/cpu.rs
index d0365ba..9416783 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -51,6 +51,8 @@ impl CPU {
             x if x == Instruction::JNZ as u8 => self.jnz(mem),
             x if x == Instruction::CMP_RI as u8 => self.cmp_ri(mem),
             x if x == Instruction::CMP_RR as u8 => self.cmp_rr(mem),
+            x if x == Instruction::MUL as u8 => self.mul(mem),
+            x if x == Instruction::DIV as u8 => self.div(mem),
             x if x == Instruction::HLT as u8 => self.halt(),
             _ => panic!("Unknown opcode {:02X}", opcode),
         }
@@ -298,6 +300,42 @@ impl CPU {
         self.carry = borrow;
     }
 
+    pub fn mul(&mut self, mem: &Memory) {
+        let dest = mem.read(self.pc); self.inc_pc();
+        let src  = mem.read(self.pc); self.inc_pc();
+
+        let lhs = self.get_reg(dest);
+        let rhs = self.get_reg(src);
+
+        let result16 = (lhs as u16) * (rhs as u16);
+        let result8  = (result16 & 0xFF) as u8;
+
+        self.set_reg(dest, result8);
+
+        self.zero  = result8 == 0;
+        self.carry = result16 > 0xFF;
+    }
+
+    pub fn div(&mut self, mem: &Memory) {
+        let dest = mem.read(self.pc); self.inc_pc();
+        let src  = mem.read(self.pc); self.inc_pc();
+
+        let lhs = self.get_reg(dest);
+        let rhs = self.get_reg(src);
+
+        if rhs == 0 {
+            panic!("Division by zero");
+            // OR: set halted = true
+            // OR: define a syscall/exception later
+        }
+
+        let result = lhs / rhs;
+
+        self.set_reg(dest, result);
+
+        self.zero = result == 0;
+        // carry unchanged
+    }
 
     fn get_reg(&self, r: u8) -> u8 {
         match r {
@@ -305,7 +343,7 @@ impl CPU {
             1 => self.b,
             2 => self.c,
             3 => self.d,
-            _ => 0,
+            _ => panic!("Invalid Register"),
         }
     }
 
@@ -315,7 +353,7 @@ impl CPU {
             1 => self.b = val,
             2 => self.c = val,
             3 => self.d = val,
-            _ => {},
+            _ => panic!("Invalid register"),
         }
     }
 
diff --git a/src/instructions.rs b/src/instructions.rs
index bfc4fc6..9f81b9a 100644
--- a/src/instructions.rs
+++ b/src/instructions.rs
@@ -12,6 +12,8 @@ pub enum Instruction {
     JNZ = 0x06,
     CMP_RI = 0x07,
     CMP_RR = 0x09,
+    MUL = 0x0C,
+    DIV = 0x0D,
     HLT = 0xFF,
 }
 
@@ -25,6 +27,8 @@ impl Instruction {
             0x05 => "JZ",
             0x06 => "JNZ",
             0x07 | 0x09 => "CMP",
+            0x0C => "MUL",
+            0x0D => "DIV",
             0xFF => "HLT",
             _ => "???",
         }