Make memory an object

memory.go

@@ -0,0 +1,39 @@
+package vm
+
+import "fmt"
+
+type memory struct {
+	entries []uint64
+}
+
+func newMemory(size uint64) *memory {
+	return &memory{
+		entries: make([]uint64, size),
+	}
+}
+
+func (mem *memory) readUnsigned(index uint64) (uint64, error) {
+	if index >= uint64(len(mem.entries)) {
+		return 0, fmt.Errorf("Invalid memory index: %016x", index)
+	}
+
+	return mem.entries[index], nil
+}
+
+func (mem *memory) mustReadUnsigned(index uint64) uint64 {
+	value, err := mem.readUnsigned(index)
+	if err != nil {
+		panic(err)
+	}
+	return value
+}
+
+func (mem *memory) writeUnsigned(index uint64, value uint64) error {
+	if index >= uint64(len(mem.entries)) {
+		return fmt.Errorf("Invalid memory index: %016x", index)
+	}
+
+	mem.entries[index] = value
+
+	return nil
+}

state.go

@@ -15,13 +15,14 @@ type State struct {
 	instructionIndex int64
 
 	comparisonResult bool
-	globalMemory     [globalMemoryEntries]uint64
+	globalMemory     *memory
 	stack            []*stackFrame
 }
 
 func NewState(functions [][]*Instruction) (*State, error) {
 	return &State{
 		functions:    functions,
+		globalMemory: newMemory(globalMemoryEntries),
 	}, nil
 }
 
@@ -97,11 +98,11 @@ func (state *State) readUnsigned(op *Operand) uint64 {
 		return state.stackFrame().functionMemory[op.Value]
 
 	case GlobalMemoryIndex:
-		if op.Value >= globalMemoryEntries {
-			state.setError(fmt.Errorf("Invalid global memory index: %016x", op.Value))
-			return 0
+		value, err := state.globalMemory.readUnsigned(op.Value)
+		if err != nil {
+			state.setError(err)
 		}
-		return state.globalMemory[op.Value]
+		return value
 
 	default:
 		state.setError(fmt.Errorf("Unknown operand type: 0x%02x", op.Type))
@@ -126,11 +127,10 @@ func (state *State) writeUnsigned(op *Operand, value uint64) {
 		state.stackFrame().functionMemory[op.Value] = value
 
 	case GlobalMemoryIndex:
-		if op.Value >= globalMemoryEntries {
-			state.setError(fmt.Errorf("Invalid global memory index: %016x", op.Value))
-			return
+		err := state.globalMemory.writeUnsigned(op.Value, value)
+		if err != nil {
+			state.setError(err)
 		}
-		state.globalMemory[op.Value] = value
 
 	default:
 		state.setError(fmt.Errorf("Unknown operand type: 0x%02x", op.Type))

state_test.go

@@ -41,7 +41,7 @@ func TestFirst(t *testing.T) {
 		t.Fatal(state)
 	}
 
-	if state.globalMemory[0] != 3 {
-		t.Fatal(state.globalMemory[0])
+	if state.globalMemory.mustReadUnsigned(0) != 3 {
+		t.Fatal(state.globalMemory.mustReadUnsigned(0))
 	}
 }