Use bitwise AND to mask instruction literal value properly

This can't really be done at the microcode level, because it depends
on the word and opcode lengths...

Author: epall

lib/Computer.Build.rb

@@ -198,9 +198,10 @@ def initialize(op, *operands)
 
     def opcode
       return {
-        :complement => "101",
-        :add => "010",
-        :subtract => "110"}[@op]
+        :complement => "011",
+        :and => "001",
+        :add => "100",
+        :subtract => "101"}[@op]
     end
   end
 
@@ -312,6 +313,10 @@ def add(operand1, operand2)
   Computer::ALUOperation.new(:add, operand1, operand2)
 end
 
+def bitwise_and(operand1, operand2)
+  Computer::ALUOperation.new(:and, operand1, operand2)
+end
+
 def subtract(operand1, operand2)
   Computer::ALUOperation.new(:subtract, operand1, operand2)
 end

lib/McCalla.rb

@@ -22,7 +22,7 @@
   end
 
   computer.instruction "add" do |i|
-    i.move :MA, :IR
+    i.move :MA, bitwise_and(:IR, 0x0F)
     i.move :A, add(:A, :MD)
   end
 
@@ -42,6 +42,6 @@
   end
 
   computer.instruction "jmp" do |i|
-    i.move :pc, :IR
+    i.move :pc, bitwise_and(:IR, 0x0F)
   end
 end