Actually make MovType work

src/vm.rs

@@ -40,6 +40,15 @@ pub enum ExitInstruction {
 }
 
 pub enum MovType { Mov, Add, Xor }
+impl MovType {
+    fn merge(&self, old_value: Sample, new_value: Sample) -> Sample {
+        match self {
+            MovType::Mov => new_value,
+            MovType::Add => Sample(old_value.0 + new_value.0),
+            MovType::Xor => Sample(old_value.0 ^ new_value.0)
+        }
+    }
+}
 
 #[derive(Clone, Copy)] pub enum MovDst { L(RegL), R(RegR), Z(RegZ), Ix }
 #[derive(Clone, Copy)] pub enum MovSrc { A(RegA), L(RegL), R(RegR), Z(RegZ), Ix, Imm(Sample) }
@@ -155,20 +164,20 @@ impl Scope {
             }
             MovDst::R(RegR(r)) => {
                 let r = r as usize;
-                self.reg_rs[r] = value; return
+                self.reg_rs[r] = ty.merge(self.reg_rs[r], value); return
             }
             MovDst::Z(RegZ(z)) => {
                 let z = z as usize;
                 (&mut self.reg_zs[z], &self.loop_zs[z])
             }
-            MovDst::Ix => { self.ix = value; return }
+            MovDst::Ix => { self.ix = ty.merge(self.ix, value); return }
         };
 
         let mut ix = flat_ix + offset;
         if loop_.length != 0 { ix %= loop_.length; }
         ix += chan.formal().start + loop_.start;
 
-        chan[ix] = value
+        chan[ix] = ty.merge(chan[ix], value)
     }
 
     fn replace(&mut self, dst: OupDst, value: Channel) {