[ignition] Rewrite reverse iterator as random iterator

src/interpreter/bytecode-array-random-iterator.h

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_INTERPRETER_BYTECODE_ARRAY_RANDOM_ITERATOR_H_
+#define V8_INTERPRETER_BYTECODE_ARRAY_RANDOM_ITERATOR_H_
+
+#include "src/interpreter/bytecode-array-accessor.h"
+#include "src/zone/zone-containers.h"
+#include "src/zone/zone.h"
+
+namespace v8 {
+namespace internal {
+namespace interpreter {
+
+class V8_EXPORT_PRIVATE BytecodeArrayRandomIterator final
+    : public BytecodeArrayAccessor {
+ public:
+  explicit BytecodeArrayRandomIterator(Handle<BytecodeArray> bytecode_array,
+                                       Zone* zone);
+
+  BytecodeArrayRandomIterator& operator++() {
+    ++current_index_;
+    UpdateOffsetFromIndex();
+    return *this;
+  }
+  BytecodeArrayRandomIterator& operator--() {
+    --current_index_;
+    UpdateOffsetFromIndex();
+    return *this;
+  }
+
+  BytecodeArrayRandomIterator& operator+=(int offset) {
+    current_index_ += offset;
+    UpdateOffsetFromIndex();
+    return *this;
+  }
+
+  BytecodeArrayRandomIterator& operator-=(int offset) {
+    current_index_ -= offset;
+    UpdateOffsetFromIndex();
+    return *this;
+  }
+
+  int current_index() const { return current_index_; }
+
+  size_t size() const { return offsets_.size(); }
+
+  void GoToIndex(int index) {
+    current_index_ = index;
+    UpdateOffsetFromIndex();
+  }
+  void GoToStart() {
+    current_index_ = 0;
+    UpdateOffsetFromIndex();
+  }
+  void GoToEnd() {
+    DCHECK_LT(offsets_.size() - 1, static_cast<size_t>(INT_MAX));
+    current_index_ = static_cast<int>(offsets_.size() - 1);
+    UpdateOffsetFromIndex();
+  }
+
+  bool IsValid() const;
+
+ private:
+  ZoneVector<int> offsets_;
+  int current_index_;
+
+  void UpdateOffsetFromIndex();
+
+  DISALLOW_COPY_AND_ASSIGN(BytecodeArrayRandomIterator);
+};
+
+}  // namespace interpreter
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_INTERPRETER_BYTECODE_ARRAY_RANDOM_ITERATOR_H_