From d72709642270c3eed897e6889f20ddbb67264888 Mon Sep 17 00:00:00 2001
From: Scott Richmond <kredati@users.noreply.github.com>
Date: Wed, 18 Jun 2025 14:12:10 -0400
Subject: [PATCH] VM instructions now take 3 bytes

---
 src/vm.rs | 66 ++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 46 insertions(+), 20 deletions(-)

diff --git a/src/vm.rs b/src/vm.rs
index 2d6cbd9..8555a78 100644
--- a/src/vm.rs
+++ b/src/vm.rs
@@ -57,7 +57,7 @@ impl CallFrame {
         let Value::Fn(ref function) = self.function else {
             unreachable!()
         };
-        &function.chunk(self.arity)
+        function.chunk(self.arity)
     }
 }
 
@@ -76,6 +76,11 @@ impl fmt::Display for CallFrame {
     }
 }
 
+fn combine_bytes(high: u8, low: u8) -> usize {
+    let out = ((high as u16) << 8) + low as u16;
+    out as usize
+}
+
 pub struct Vm {
     pub stack: Vec<Value>,
     pub call_stack: Vec<CallFrame>,
@@ -205,46 +210,61 @@ impl Vm {
                     self.ip += 2;
                 }
                 Jump => {
-                    let jump_len = self.chunk().bytecode[self.ip + 1];
-                    self.ip += jump_len as usize + 2;
+                    let high = self.chunk().bytecode[self.ip + 1];
+                    let low = self.chunk().bytecode[self.ip + 2];
+                    let jump_len = combine_bytes(high, low);
+                    // let jump_len = self.chunk().bytecode[self.ip + 1];
+                    self.ip += jump_len + 3;
                 }
                 JumpBack => {
-                    let jump_len = self.chunk().bytecode[self.ip + 1];
-                    self.ip -= jump_len as usize;
+                    let high = self.chunk().bytecode[self.ip + 1];
+                    let low = self.chunk().bytecode[self.ip + 2];
+                    let jump_len = combine_bytes(high, low);
+                    // let jump_len = self.chunk().bytecode[self.ip + 1];
+                    self.ip -= jump_len;
                 }
                 JumpIfFalse => {
-                    let jump_len = self.chunk().bytecode[self.ip + 1];
+                    let high = self.chunk().bytecode[self.ip + 1];
+                    let low = self.chunk().bytecode[self.ip + 2];
+                    let jump_len = combine_bytes(high, low);
+                    // let jump_len = self.chunk().bytecode[self.ip + 1];
                     let cond = self.pop();
                     match cond {
                         Value::Nil | Value::False => {
-                            self.ip += jump_len as usize + 2;
+                            self.ip += jump_len + 3;
                         }
                         _ => {
-                            self.ip += 2;
+                            self.ip += 3;
                         }
                     }
                 }
                 JumpIfTrue => {
-                    let jump_len = self.chunk().bytecode[self.ip + 1];
+                    let high = self.chunk().bytecode[self.ip + 1];
+                    let low = self.chunk().bytecode[self.ip + 2];
+                    let jump_len = combine_bytes(high, low);
+                    // let jump_len = self.chunk().bytecode[self.ip + 1];
                     let cond = self.pop();
                     match cond {
                         Value::Nil | Value::False => {
-                            self.ip += 2;
+                            self.ip += 3;
                         }
                         _ => {
-                            self.ip += jump_len as usize + 2;
+                            self.ip += jump_len + 3;
                         }
                     }
                 }
                 JumpIfZero => {
-                    let jump_len = self.chunk().bytecode[self.ip + 1];
+                    let high = self.chunk().bytecode[self.ip + 1];
+                    let low = self.chunk().bytecode[self.ip + 2];
+                    let jump_len = combine_bytes(high, low);
+                    // let jump_len = self.chunk().bytecode[self.ip + 1];
                     let cond = self.pop();
                     match cond {
                         Value::Number(x) if x <= 0.0 => {
-                            self.ip += jump_len as usize + 2;
+                            self.ip += jump_len as usize + 3;
                         }
                         Value::Number(..) => {
-                            self.ip += 2;
+                            self.ip += 3;
                         }
                         _ => return self.panic("repeat requires a number"),
                     }
@@ -542,19 +562,25 @@ impl Vm {
                     self.ip += 1;
                 }
                 JumpIfNoMatch => {
-                    let jump_len = self.chunk().bytecode[self.ip + 1] as usize;
+                    let high = self.chunk().bytecode[self.ip + 1];
+                    let low = self.chunk().bytecode[self.ip + 2];
+                    let jump_len = combine_bytes(high, low);
+                    // let jump_len = self.chunk().bytecode[self.ip + 1] as usize;
                     if !self.matches {
-                        self.ip += jump_len + 2;
+                        self.ip += jump_len + 3;
                     } else {
-                        self.ip += 2;
+                        self.ip += 3;
                     }
                 }
                 JumpIfMatch => {
-                    let jump_len = self.chunk().bytecode[self.ip + 1] as usize;
+                    let high = self.chunk().bytecode[self.ip + 1];
+                    let low = self.chunk().bytecode[self.ip + 2];
+                    let jump_len = combine_bytes(high, low);
+                    // let jump_len = self.chunk().bytecode[self.ip + 1] as usize;
                     if self.matches {
-                        self.ip += jump_len + 2;
+                        self.ip += jump_len + 3;
                     } else {
-                        self.ip += 2;
+                        self.ip += 3;
                     }
                 }
                 TypeOf => {