From 803c6267d2cab4b33310bb27d574ce750622d41d Mon Sep 17 00:00:00 2001
From: Marco Thomas <github@marcothms.de>
Date: Wed, 2 Jul 2025 20:32:13 +0900
Subject: [PATCH] ft(interpreter): impl mul and div

---
 src/interpreter/interpreter.rs | 32 ++++++++++++++++++++++
 src/operands.rs                | 49 ++++++++++++++++++----------------
 2 files changed, 58 insertions(+), 23 deletions(-)

diff --git a/src/interpreter/interpreter.rs b/src/interpreter/interpreter.rs
index b69ec7b..f1e2bd3 100644
--- a/src/interpreter/interpreter.rs
+++ b/src/interpreter/interpreter.rs
@@ -668,10 +668,42 @@ impl Interpreter {
                 /*
                  * MUL
                  */
+                Mnemonic::MUL(target) => {
+                    let src = self.computer.read_modrm(target)?;
+                    let dest = self.computer.regs.ax.read();
+                    let (ax, dx) = src.mul(dest.into());
+                    self.computer.regs.ax.write(ax);
+                    self.computer.regs.dx.write(dx);
+                    self.computer.flags.of = if dx == 0 { false } else { true };
+                    self.computer.flags.cf = if dx == 0 { false } else { true };
+                }
+                Mnemonic::IMUL(_) => todo!(),
 
                 /*
                  * DIV
                  */
+                Mnemonic::DIV(target) => {
+                    // byte: Unsigned divide AX by r/m8, with result stored in AL ← Quotient, AH ← Remainder.
+                    // word: Unsigned divide DX:AX by r/m16, with result stored in AX ← Quotient, DX ← Remainder.
+                    let src = self.computer.read_modrm(target)?;
+                    let ax = self.computer.regs.ax.read();
+                    match src {
+                        ImmediateOperand::Byte(b) => {
+                            self.computer.regs.ax.lower = (ax / b as Word) as Byte;
+                            self.computer.regs.ax.upper = (ax % b as Word) as Byte;
+                        }
+                        ImmediateOperand::Word(w) => {
+                            let dx = self.computer.regs.dx.read();
+                            let num: u32 = ((dx as u32) << 16) | (ax as u32);
+                            let quot: u16 = (num / w as u32) as Word;
+                            let rem: u16 = (num % w as u32) as Word;
+
+                            self.computer.regs.ax.write(quot);
+                            self.computer.regs.dx.write(rem);
+                        }
+                    }
+                }
+                Mnemonic::IDIV(_) => todo!(),
 
                 /*
                  * HLT
diff --git a/src/operands.rs b/src/operands.rs
index e157246..809f10d 100644
--- a/src/operands.rs
+++ b/src/operands.rs
@@ -107,6 +107,32 @@ impl ImmediateOperand {
             Self::Word(word) => return (word >> 15) == 1,
         }
     }
+
+    /// Multiply values and return the extended u32, split into two words.
+    pub fn mul(&self, other: Self) -> (Word, Word) {
+        let result: u32 = match self {
+            Self::Byte(lhsb) => match other {
+                Self::Byte(rhsb) => *lhsb as u32 * rhsb as u32,
+                Self::Word(rhsw) => match other.sign_extend() {
+                    Self::Word(lhsw) => lhsw as u32 * rhsw as u32,
+                    _ => panic!("unreachable"),
+                },
+            },
+            Self::Word(lhsw) => match other {
+                Self::Word(rhsw) => *lhsw as u32 * rhsw as u32,
+                Self::Byte(_) => match other.sign_extend() {
+                    Self::Word(rhsw) => *lhsw as u32 * rhsw as u32,
+                    _ => panic!("unreachable"),
+                },
+            },
+        };
+
+        let bytes = result.to_le_bytes();
+        let lower = Word::from_le_bytes([bytes[0], bytes[1]]);
+        let upper = Word::from_le_bytes([bytes[2], bytes[3]]);
+
+        (lower, upper)
+    }
 }
 
 impl PartialOrd for ImmediateOperand {
@@ -262,29 +288,6 @@ impl Sub<Byte> for ImmediateOperand {
         }
     }
 }
-impl Mul for ImmediateOperand {
-    type Output = Self;
-
-    fn mul(self, other: Self) -> Self {
-        match self {
-            ImmediateOperand::Byte(lhsb) => match other {
-                ImmediateOperand::Byte(rhsb) => ImmediateOperand::Byte(lhsb.wrapping_mul(rhsb)),
-                ImmediateOperand::Word(rhsw) => ImmediateOperand::Word(match other.sign_extend() {
-                    ImmediateOperand::Word(lhsw) => lhsw.wrapping_mul(rhsw),
-                    _ => panic!("unreachable"),
-                }),
-            },
-            ImmediateOperand::Word(lhsw) => match other {
-                ImmediateOperand::Word(rhsw) => ImmediateOperand::Word(lhsw.wrapping_mul(rhsw)),
-                ImmediateOperand::Byte(_) => ImmediateOperand::Word(match other.sign_extend() {
-                    ImmediateOperand::Word(rhsw) => lhsw.wrapping_mul(rhsw),
-                    _ => panic!("unreachable"),
-                }),
-            },
-        }
-    }
-}
-
 impl Shl for ImmediateOperand {
     type Output = Self;