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v8/include/cppgc/internal/base-page-handle.h

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+// Copyright 2022 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 INCLUDE_CPPGC_INTERNAL_BASE_PAGE_HANDLE_H_
+#define INCLUDE_CPPGC_INTERNAL_BASE_PAGE_HANDLE_H_
+
+#include "cppgc/heap-handle.h"
+#include "cppgc/internal/api-constants.h"
+#include "cppgc/internal/logging.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+// The class is needed in the header to allow for fast access to HeapHandle in
+// the write barrier.
+class BasePageHandle {
+ public:
+  static V8_INLINE BasePageHandle* FromPayload(void* payload) {
+    return reinterpret_cast<BasePageHandle*>(
+        (reinterpret_cast<uintptr_t>(payload) &
+         ~(api_constants::kPageSize - 1)) +
+        api_constants::kGuardPageSize);
+  }
+  static V8_INLINE const BasePageHandle* FromPayload(const void* payload) {
+    return FromPayload(const_cast<void*>(payload));
+  }
+
+  HeapHandle& heap_handle() { return heap_handle_; }
+  const HeapHandle& heap_handle() const { return heap_handle_; }
+
+ protected:
+  explicit BasePageHandle(HeapHandle& heap_handle) : heap_handle_(heap_handle) {
+    CPPGC_DCHECK(reinterpret_cast<uintptr_t>(this) % api_constants::kPageSize ==
+                 api_constants::kGuardPageSize);
+  }
+
+  HeapHandle& heap_handle_;
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_BASE_PAGE_HANDLE_H_