1 files changed, 111 insertions, 0 deletions
diff --git a/js/src/ds/FixedLengthVector.h b/js/src/ds/FixedLengthVector.h
new file mode 100644
index 0000000000..64ae459ec4
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+++ b/js/src/ds/FixedLengthVector.h
@@ -0,0 +1,111 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef ds_FixedLengthVector_h
+#define ds_FixedLengthVector_h
+
+#include "mozilla/Assertions.h"             // MOZ_ASSERT
+#include "mozilla/OperatorNewExtensions.h"  // mozilla::KnownNotNull
+
+#include <stddef.h>  // size_t
+
+#include "js/Utility.h"    // js_free
+#include "vm/JSContext.h"  // JSContext
+
+namespace js {
+
+// A dynamically-allocated fixed-length vector with bounds checking assertions.
+template <typename T>
+class FixedLengthVector {
+  // The pointer to the storage.
+  T* data_ = nullptr;
+
+  // The size of the storage.
+  size_t length_ = 0;
+
+ public:
+  FixedLengthVector() = default;
+
+  FixedLengthVector(FixedLengthVector&) = delete;
+  FixedLengthVector(FixedLengthVector&&) = default;
+
+  ~FixedLengthVector() {
+    if (initialized()) {
+      js_free(data_);
+    }
+  }
+
+  size_t length() const { return length_; }
+
+  bool initialized() const { return !!data_; }
+
+  // Allocate the storage with the given size, wihtout calling constructor.
+  //
+  // If the allocation fails, this returns false and sets the
+  // pending exception on the given context.
+  [[nodiscard]] bool allocateUninitialized(JSContext* cx, size_t length) {
+    MOZ_ASSERT(!initialized());
+
+    length_ = length;
+    data_ = cx->pod_malloc<T>(length);
+    if (MOZ_UNLIKELY(!data_)) {
+      return false;
+    }
+
+    return true;
+  }
+
+  // Allocate the storage with the given size and call default constructor.
+  //
+  // If the allocation fails, this returns false and sets the
+  // pending exception on the given context.
+  [[nodiscard]] bool allocate(JSContext* cx, size_t length) {
+    if (!allocateUninitialized(cx, length)) {
+      return false;
+    }
+
+    for (size_t i = 0; i < length; i++) {
+      new (mozilla::KnownNotNull, &data_[i]) T();
+    }
+    return true;
+  }
+
+  T* begin() {
+    MOZ_ASSERT(initialized());
+    return data_;
+  }
+
+  const T* begin() const {
+    MOZ_ASSERT(initialized());
+    return data_;
+  }
+
+  T* end() {
+    MOZ_ASSERT(initialized());
+    return data_ + length_;
+  }
+
+  const T* end() const {
+    MOZ_ASSERT(initialized());
+    return data_ + length_;
+  }
+
+  T& operator[](size_t index) {
+    MOZ_ASSERT(initialized());
+    MOZ_ASSERT(index < length_);
+    return begin()[index];
+  }
+
+  const T& operator[](size_t index) const {
+    MOZ_ASSERT(initialized());
+    MOZ_ASSERT(index < length_);
+    return begin()[index];
+  }
+};
+
+}  // namespace js
+
+#endif  // ds_FixedLengthVector_h