Merge pull request #13 from skx/12-stack

Fix stack removal.

cpu/cpu.go

@@ -130,7 +130,9 @@ func (c *CPU) LoadBytes(data []byte) {
 
 	// Copy contents of file to our memory region
 	for i := 0; i < len(data); i++ {
-		c.mem[i] = data[i]
+		// Addition to fix a linter warning suggesting the used
+		// of `copy`.
+		c.mem[i+0] = data[i+0]
 	}
 }
 

cpu/stack.go

@@ -43,7 +43,12 @@ func (s *Stack) Pop() (int, error) {
 		return 0, errors.New("Pop from an empty stack")
 	}
 
-	result := s.entries[0]
-	s.entries = append(s.entries[:0], s.entries[1:]...)
-	return result, nil
+	// get top
+	l := len(s.entries)
+	top := s.entries[l-1]
+
+	// truncate
+	s.entries = s.entries[:l-1]
+
+	return top, nil
 }

cpu/stack_test.go

@@ -55,3 +55,60 @@ func TestEmptyStack(t *testing.T) {
 		t.Errorf("should receive an error popping an empty stack!")
 	}
 }
+
+
+// Test issue #12 - stack is FIFO, not LIFO
+func TestIssue12(t *testing.T) {
+
+	s := NewStack()
+	s.Push(10)  // top is 10
+	s.Push(20)  // top is 20, then 10
+	s.Push(30)  // top is 30, then 20, then 10
+
+	// Ensure the contents are as expected
+	if s.entries[0] != 10 { t.Fatalf("Unexpected result")}
+	if s.entries[1] != 20 { t.Fatalf("Unexpected result")}
+	if s.entries[2] != 30 { t.Fatalf("Unexpected result")}
+	if s.Size() != 3 { t.Fatalf("wrong length") }
+
+
+	// popping should remove in expected order
+	val,err := s.Pop()
+	if err != nil {
+		t.Fatalf("unexpected error")
+	}
+	if val != 30 {
+		t.Fatalf("stack is wrong")
+	}
+
+	// Contents should still be what we expect,
+	// after removing one entry
+	if s.entries[0] != 10 { t.Fatalf("Unexpected result")}
+	if s.entries[1] != 20 { t.Fatalf("Unexpected result")}
+	if s.Size() != 2 { t.Fatalf("wrong length") }
+
+	// Get the middle value
+	val,err = s.Pop()
+	if err != nil {
+		t.Fatalf("unexpected error")
+	}
+	if val != 20 {
+		t.Fatalf("stack is wrong")
+	}
+
+
+	if s.entries[0] != 10 { t.Fatalf("Unexpected result")}
+	if s.Size() != 1 { t.Fatalf("wrong length")}
+	val,err = s.Pop()
+	if err != nil {
+		t.Fatalf("unexpected error")
+	}
+	if val != 10 {
+		t.Fatalf("stack is wrong")
+	}
+
+	if !s.Empty() {
+		t.Fatalf("stack should be empty")
+	}
+	if s.Size() != 0 { t.Fatalf("wrong length")}
+}