diff --git a/lib/Machine.ml b/lib/Machine.ml
index 4450ce4..27d5c30 100644
--- a/lib/Machine.ml
+++ b/lib/Machine.ml
@@ -87,54 +87,58 @@ let create code =
 
 let dispatch ?(trace = false) (Machine m) (pc : int) =
   let pc = ref pc in
+  let trace op l =
+    if trace then
+      let instr = Instr.of_int op in
+      perform (Trace (!pc, instr, l))
+  in
 
   while true do
-    pc := !pc land 0xffff;
-
-    let op = Bytes.get_uint8 m.data !pc in
-    let instr = Instr.of_int op in
-    let trace l = if trace then perform (Trace (!pc, instr, l)) in
-
+    let op = Bytes.get_uint8 m.data (!pc land 0xffff) in
     pc := (!pc + 1) land 0xffff;
 
+    let short = op land 0x20 <> 0 in
+    let keep = op land 0x80 <> 0 in
+    let return = op land 0x40 <> 0 in
+    let opcode = op land 0x1f in
+
     match op with
     | 0x00 -> pc := perform BRK
     | 0x20 (* JCI *) ->
         let cond = pop1 m.stack in
         let addr = Util.get_int16_wrap ~wrap:0xffff m.data !pc in
-        trace [ Bytes.get_uint16_be m.data !pc; cond ];
+        trace op [ Bytes.get_uint16_be m.data !pc; cond ];
         if cond != 0 then pc := !pc + addr + 2 else pc := !pc + 2
     | 0x40 (* JMI *) ->
         let addr = Util.get_int16_wrap ~wrap:0xffff m.data !pc in
-        trace [ Bytes.get_uint16_be m.data !pc ];
+        trace op [ Bytes.get_uint16_be m.data !pc ];
         pc := !pc + addr + 2
     | 0x60 (* JSI *) ->
         let addr = Util.get_int16_wrap ~wrap:0xffff m.data !pc in
-        trace [ Bytes.get_uint16_be m.data !pc ];
+        trace op [ Bytes.get_uint16_be m.data !pc ];
         push2 m.callstack (!pc + 2);
         pc := !pc + addr + 2
     | 0x80 (* LIT *) ->
         let lit = Bytes.get_uint8 m.data !pc in
-        trace [ lit ];
+        trace op [ lit ];
         push1 m.stack lit;
         pc := !pc + 1
     | 0xa0 (* LIT2 *) ->
         let lit = Util.get_uint16_wrap ~wrap:0xffff m.data !pc in
-        trace [ lit ];
+        trace op [ lit ];
         push2 m.stack lit;
         pc := !pc + 2
     | 0xc0 (* LITr *) ->
         let lit = Bytes.get_uint8 m.data !pc in
-        trace [ lit ];
+        trace op [ lit ];
         push1 m.callstack lit;
         pc := !pc + 1
     | 0xe0 (* LIT2r *) ->
         let lit = Util.get_uint16_wrap ~wrap:0xffff m.data !pc in
-        trace [ lit ];
+        trace op [ lit ];
         push2 m.callstack lit;
         pc := !pc + 2
     | _ -> begin
-        let (Instruction { short; keep; return; opcode }) = Instr.of_int op in
         let stk = if return then m.callstack else m.stack in
         let stk' = if return then m.stack else m.callstack in
         let mode =
@@ -143,166 +147,166 @@ let dispatch ?(trace = false) (Machine m) (pc : int) =
         match[@warning "-8"] opcode with
         | 0x01 (* INC *) ->
             let r = pop mode stk in
-            trace [ r ];
+            trace op [ r ];
             push mode stk (r + 1)
-        | 0x02 (* POP *) -> trace [ pop mode stk ]
+        | 0x02 (* POP *) -> trace op [ pop mode stk ]
         | 0x03 (* NIP *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             push mode stk b
         | 0x04 (* SWP *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             push mode stk b;
             push mode stk a
         | 0x05 (* ROT *) ->
             let c = pop mode stk in
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b; c ];
+            trace op [ a; b; c ];
             push mode stk b;
             push mode stk c;
             push mode stk a
         | 0x06 (* DUP *) ->
             let a = pop mode stk in
-            trace [ a ];
+            trace op [ a ];
             push mode stk a;
             push mode stk a
         | 0x07 (* OVR *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             push mode stk a;
             push mode stk b;
             push mode stk a
         | 0x08 (* EQU *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             pushbyte mode stk (if a = b then 1 else 0)
         | 0x09 (* NEQ *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             pushbyte mode stk (if a != b then 1 else 0)
         | 0x0a (* GTH *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             pushbyte mode stk (if a > b then 1 else 0)
         | 0x0b (* LTH *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             pushbyte mode stk (if a < b then 1 else 0)
         | 0x0c (* JMP *) ->
             let addr = pop mode stk in
-            trace [ addr ];
+            trace op [ addr ];
             if short then pc := addr else pc := !pc + Util.uint8_to_int8 addr
         | 0x0d (* JCN *) ->
             let addr = pop mode stk in
             let cond = popbyte mode stk in
-            trace [ cond; addr ];
+            trace op [ cond; addr ];
             if cond != 0 then
               if short then pc := addr else pc := !pc + Util.uint8_to_int8 addr
         | 0x0e (* JSR *) ->
             push2 m.callstack !pc;
             let addr = pop mode stk in
-            trace [ addr ];
+            trace op [ addr ];
             if short then pc := addr else pc := !pc + Util.uint8_to_int8 addr
         | 0x0f (* STH *) ->
             let a = pop mode stk in
-            trace [ a ];
+            trace op [ a ];
             push mode stk' a
         | 0x10 (* LDZ *) ->
             let addr = popbyte mode stk in
-            trace [ addr ];
+            trace op [ addr ];
             push mode stk
               (if short then Util.get_uint16_wrap m.data addr
                else Bytes.get_uint8 m.data addr)
         | 0x11 (* STZ *) ->
             let addr = popbyte mode stk in
             let v = pop mode stk in
-            trace [ v; addr ];
+            trace op [ v; addr ];
             if short then Util.set_uint16_wrap m.data addr v
             else Bytes.set_uint8 m.data addr v
         | 0x12 (* LDR *) ->
             let addr = !pc + Util.uint8_to_int8 (popbyte mode stk) in
-            trace [ addr ];
+            trace op [ addr ];
             push mode stk
               (if short then Util.get_uint16_wrap ~wrap:0xffff m.data addr
                else Bytes.get_uint8 m.data addr)
         | 0x13 (* STR *) ->
             let addr = !pc + Util.uint8_to_int8 (popbyte mode stk) in
             let v = pop mode stk in
-            trace [ v; addr ];
+            trace op [ v; addr ];
             if short then Util.set_uint16_wrap ~wrap:0xffff m.data addr v
             else Bytes.set_uint8 m.data addr v
         | 0x14 (* LDA *) ->
             let addr = popshort mode stk in
-            trace [ addr ];
+            trace op [ addr ];
             push mode stk
               (if short then Util.get_uint16_wrap ~wrap:0xffff m.data addr
                else Bytes.get_uint8 m.data addr)
         | 0x15 (* STA *) ->
             let addr = popshort mode stk in
             let v = pop mode stk in
-            trace [ v; addr ];
+            trace op [ v; addr ];
             if short then Util.set_uint16_wrap ~wrap:0xffff m.data addr v
             else Bytes.set_uint8 m.data addr v
         | 0x16 (* DEI *) ->
             let port = popbyte mode stk in
-            trace [ port ];
+            trace op [ port ];
             push mode stk
               (perform (DEI ((if short then `Short else `Byte), port)))
         | 0x17 (* DEO *) ->
             let port = popbyte mode stk in
             let value = pop mode stk in
-            trace [ value; port ];
+            trace op [ value; port ];
             if short then Util.set_uint16_wrap m.dev port value
             else Bytes.set_uint8 m.dev port value;
             perform (DEO (port, value))
         | 0x18 (* ADD *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             push mode stk (a + b)
         | 0x19 (* SUB *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             push mode stk (a - b)
         | 0x1a (* MUL *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             push mode stk (a * b)
         | 0x1b (* DIV *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             push mode stk (if b = 0 then 0 else a / b)
         | 0x1c (* AND *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             push mode stk (a land b)
         | 0x1d (* ORA *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             push mode stk (a lor b)
         | 0x1e (* EOR *) ->
             let b = pop mode stk in
             let a = pop mode stk in
-            trace [ a; b ];
+            trace op [ a; b ];
             push mode stk (a lxor b)
         | 0x1f (* SFT *) ->
             let sft = popbyte mode stk in
             let value = pop mode stk in
-            trace [ value; sft ];
+            trace op [ value; sft ];
             push mode stk ((value lsr (sft land 0xf)) lsl sft lsr 4)
       end
   done