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")}
+}