1 files changed, 28 insertions, 16 deletions
diff --git a/src/forth/vm.rs b/src/forth/vm.rs
index e7c3794..564a647 100644
--- a/src/forth/vm.rs
+++ b/src/forth/vm.rs
@@ -4,6 +4,10 @@ use std::ops::Index;
 
 pub type DataStackType = isize;
 
+const MIN_SPEED: DataStackType = 0;
+const MAX_SPEED: DataStackType = 10;
+const UNITS_PER_ROTATION: DataStackType = 360;
+
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub enum OpCode {
     Num(DataStackType),
@@ -41,8 +45,8 @@ pub enum OpCode {
     Say,
     Heading,
     SetHeading,
-    Velocity,
-    SetVelocity,
+    Speed,
+    SetSpeed,
     Doppler,
 }
 
@@ -124,7 +128,7 @@ pub struct VM {
 
     pub out: Vec<String>,
     pub heading: DataStackType,
-    pub velocity: DataStackType,
+    pub speed: DataStackType,
     pub doppler: DataStackType,
 }
 
@@ -151,7 +155,7 @@ impl VM {
 
             out: vec![],
             heading: 0,
-            velocity: 0,
+            speed: 0,
             doppler: 0,
         }
     }
@@ -315,13 +319,21 @@ impl VM {
                 self.stack.0.push(self.heading);
             }
             OpCode::SetHeading => {
-                self.heading = self.stack.0.pop().ok_or(RuntimeError::StackUnderflow)?;
+                let v = self.stack.0.pop().ok_or(RuntimeError::StackUnderflow)?;
+                self.heading = (UNITS_PER_ROTATION + (v % UNITS_PER_ROTATION)) % UNITS_PER_ROTATION;
             }
-            OpCode::Velocity => {
-                self.stack.0.push(self.velocity);
+            OpCode::Speed => {
+                self.stack.0.push(self.speed);
             }
-            OpCode::SetVelocity => {
-                self.velocity = self.stack.0.pop().ok_or(RuntimeError::StackUnderflow)?;
+            OpCode::SetSpeed => {
+                let v = self.stack.0.pop().ok_or(RuntimeError::StackUnderflow)?;
+                self.speed = if v < MIN_SPEED {
+                    MIN_SPEED
+                } else if v > MAX_SPEED {
+                    MAX_SPEED
+                } else {
+                    v
+                };
             }
             OpCode::Doppler => {
                 self.stack.0.push(self.doppler);
@@ -845,26 +857,26 @@ mod tests {
     }
 
     #[test]
-    fn opcode_velocity() {
+    fn opcode_speed() {
         let wordlist = wl_for(vec![vec![
-            OpCode::Velocity
+            OpCode::Speed
         ]]);
         let mut vm = VM::new(wordlist);
-        vm.velocity = 12;
+        vm.speed = 12;
         vm.run().expect("should run to completion");
         assert_eq!(vm.stack.0.len(), 1, "stack size");
-        assert_eq!(vm.stack.0[0], 12, "velocity value");
+        assert_eq!(vm.stack.0[0], 12, "speed value");
     }
 
     #[test]
-    fn opcode_setvelocity() {
+    fn opcode_setspeed() {
         let wordlist = wl_for(vec![vec![
-            OpCode::Num(3), OpCode::SetVelocity
+            OpCode::Num(3), OpCode::SetSpeed
         ]]);
         let mut vm = VM::new(wordlist);
         vm.run().expect("should run to completion");
         assert_eq!(vm.stack.0.len(), 0, "empty stack");
-        assert_eq!(vm.velocity, 3, "velocity value");
+        assert_eq!(vm.speed, 3, "speed value");
     }
 
     #[test]