Drafted operand evaluation procedure.

diff --git a/mars.scm b/mars.scm
index 2f4db9d..b1aa9db 100644 (file)
--- a/mars.scm
+++ b/mars.scm
@@ -67,8 +67,8 @@
 
 (define (execute-instr ptr)
   (let* ((instr (vector-ref core ptr))
-         (A-operand (eval-operand (instr-A-mode instr) (instr-A-num) ptr))
-         (B-operand (eval-operand (instr-B-mode instr) (instr-B-num) ptr)))
+         (A-pointer (eval-operand (instr-A-mode instr) (instr-A-num) ptr))
+         (B-pointer (eval-operand (instr-B-mode instr) (instr-B-num) ptr)))
     (case (instr-opcode instr)
       ((DAT))
       ((MOV))
@@ -90,11 +90,27 @@
                
 (define (eval-operand mode num ptr)
   (case mode
-    ((immediate))
-    ((direct))
-    ((indirect-A))
-    ((indirect-B))
-    ((pre-indirect-A))
-    ((pre-indirect-B))
-    ((post-indirect-A))
-    ((post-indirect-B))))
+    ((immediate) 0)
+    ((direct) num)
+    ((indirect-A) (+ num (instr-A-num (vector-ref core (+ ptr num)))))
+    ((indirect-B) (+ num (instr-B-num (vector-ref core (+ ptr num)))))
+    ((pre-indirect-A)
+     (let ((aux-instr (vector-ref core (+ ptr num))))
+       (instr-set-A-num! aux-instr (- 1 (instr-A-num aux-instr)))
+       (+ num (instr-A-num aux-instr))))
+    ((pre-indirect-B)
+     (let ((aux-instr (vector-ref core (+ ptr num))))
+       (instr-set-B-num! aux-instr (- 1 (instr-B-num aux-instr)))
+       (+ num (instr-B-num aux-instr))))
+    ((post-indirect-A)
+     (let* ((aux-instr (vector-ref core (+ ptr num)))
+            (old-A-num (instr-A-num aux-instr)))
+       (instr-set-A-num! aux-instr (+ 1 (instr-A-num aux-instr)))
+       (+ num old-A-num)))
+    ((post-indirect-B)
+     (let* ((aux-instr (vector-ref core (+ ptr num)))
+            (old-B-num (instr-B-num aux-instr)))
+       (instr-set-B-num! aux-instr (+ 1 (instr-B-num aux-instr)))
+       (+ num old-B-num)))
+    (else
+     (error "Unrecognized mode" mode))))