refactor: removes magic numbers in asmgenerator

src/main/wacc/backend/asmGenerator.scala

@@ -25,6 +25,8 @@ object asmGenerator {
   private val ECX = Register(D32, CX)
   private val argRegs = List(DI, SI, DX, CX, R8, R9)
 
+  private val _7_BIT_MASK = 0x7f
+
   extension [T](chain: Chain[T])
     def +(item: T): Chain[T] = chain.append(item)
 
@@ -326,7 +328,7 @@ object asmGenerator {
         op match {
           case UnaryOperator.Chr =>
             chain += Move(EAX, stack.head)
-            chain += And(EAX, ImmediateVal(-128))
+            chain += And(EAX, ImmediateVal(~_7_BIT_MASK))
             chain += Compare(EAX, ImmediateVal(0))
             chain += Jump(LabelArg(BadChrError.errLabel), Cond.NotEqual)
           case UnaryOperator.Ord => // No op needed