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+/*
+ * Copyright © 2018 Google, Inc.
+ *
+ * This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ * Google Author(s): Behdad Esfahbod
+ */
+
+#ifndef HB_NULL_HH
+#define HB_NULL_HH
+
+#include "hb.hh"
+#include "hb-meta.hh"
+
+
+/*
+ * Static pools
+ */
+
+/* Global nul-content Null pool. Enlarge as necessary. */
+
+#define HB_NULL_POOL_SIZE 640
+
+template <typename T, typename>
+struct _hb_has_min_size : hb_false_type {};
+template <typename T>
+struct _hb_has_min_size<T, hb_void_t<decltype (T::min_size)>>
+ : hb_true_type {};
+template <typename T>
+using hb_has_min_size = _hb_has_min_size<T, void>;
+#define hb_has_min_size(T) hb_has_min_size<T>::value
+
+template <typename T, typename>
+struct _hb_has_null_size : hb_false_type {};
+template <typename T>
+struct _hb_has_null_size<T, hb_void_t<decltype (T::null_size)>>
+ : hb_true_type {};
+template <typename T>
+using hb_has_null_size = _hb_has_null_size<T, void>;
+#define hb_has_null_size(T) hb_has_null_size<T>::value
+
+/* Use SFINAE to sniff whether T has min_size; in which case return the larger
+ * of sizeof(T) and T::null_size, otherwise return sizeof(T).
+ *
+ * The main purpose of this is to let structs communicate that they are not nullable,
+ * by defining min_size but *not* null_size. */
+
+/* The hard way...
+ * https://stackoverflow.com/questions/7776448/sfinae-tried-with-bool-gives-compiler-error-template-argument-tvalue-invol
+ */
+
+template <typename T, typename>
+struct _hb_null_size : hb_integral_constant<unsigned, sizeof (T)> {};
+template <typename T>
+struct _hb_null_size<T, hb_void_t<decltype (T::min_size)>>
+ : hb_integral_constant<unsigned,
+ (sizeof (T) > T::null_size ? sizeof (T) : T::null_size)> {};
+template <typename T>
+using hb_null_size = _hb_null_size<T, void>;
+#define hb_null_size(T) hb_null_size<T>::value
+
+/* These doesn't belong here, but since is copy/paste from above, put it here. */
+
+/* hb_static_size (T)
+ * Returns T::static_size if T::min_size is defined, or sizeof (T) otherwise. */
+
+template <typename T, typename>
+struct _hb_static_size : hb_integral_constant<unsigned, sizeof (T)> {};
+template <typename T>
+struct _hb_static_size<T, hb_void_t<decltype (T::static_size)>> : hb_integral_constant<unsigned, T::static_size> {};
+template <typename T>
+using hb_static_size = _hb_static_size<T, void>;
+#define hb_static_size(T) hb_static_size<T>::value
+
+template <typename T, typename>
+struct _hb_min_size : hb_integral_constant<unsigned, sizeof (T)> {};
+template <typename T>
+struct _hb_min_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::min_size> {};
+template <typename T>
+using hb_min_size = _hb_min_size<T, void>;
+#define hb_min_size(T) hb_min_size<T>::value
+
+
+/*
+ * Null()
+ */
+
+extern HB_INTERNAL
+uint64_t const _hb_NullPool[(HB_NULL_POOL_SIZE + sizeof (uint64_t) - 1) / sizeof (uint64_t)];
+
+/* Generic nul-content Null objects. */
+template <typename Type>
+struct Null {
+ static Type const & get_null ()
+ {
+ static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
+ return *reinterpret_cast<Type const *> (_hb_NullPool);
+ }
+};
+template <typename QType>
+struct NullHelper
+{
+ typedef hb_remove_const<hb_remove_reference<QType>> Type;
+ static const Type & get_null () { return Null<Type>::get_null (); }
+};
+#define Null(Type) NullHelper<Type>::get_null ()
+
+/* Specializations for arbitrary-content Null objects expressed in bytes. */
+#define DECLARE_NULL_NAMESPACE_BYTES(Namespace, Type) \
+ } /* Close namespace. */ \
+ extern HB_INTERNAL const unsigned char _hb_Null_##Namespace##_##Type[hb_null_size (Namespace::Type)]; \
+ template <> \
+ struct Null<Namespace::Type> { \
+ static Namespace::Type const & get_null () { \
+ return *reinterpret_cast<const Namespace::Type *> (_hb_Null_##Namespace##_##Type); \
+ } \
+ }; \
+ namespace Namespace { \
+ static_assert (true, "") /* Require semicolon after. */
+#define DECLARE_NULL_NAMESPACE_BYTES_TEMPLATE1(Namespace, Type, Size) \
+ } /* Close namespace. */ \
+ extern HB_INTERNAL const unsigned char _hb_Null_##Namespace##_##Type[Size]; \
+ template <typename Spec> \
+ struct Null<Namespace::Type<Spec>> { \
+ static Namespace::Type<Spec> const & get_null () { \
+ return *reinterpret_cast<const Namespace::Type<Spec> *> (_hb_Null_##Namespace##_##Type); \
+ } \
+ }; \
+ namespace Namespace { \
+ static_assert (true, "") /* Require semicolon after. */
+#define DEFINE_NULL_NAMESPACE_BYTES(Namespace, Type) \
+ const unsigned char _hb_Null_##Namespace##_##Type[sizeof (_hb_Null_##Namespace##_##Type)]
+
+/* Specializations for arbitrary-content Null objects expressed as struct initializer. */
+#define DECLARE_NULL_INSTANCE(Type) \
+ extern HB_INTERNAL const Type _hb_Null_##Type; \
+ template <> \
+ struct Null<Type> { \
+ static Type const & get_null () { \
+ return _hb_Null_##Type; \
+ } \
+ }; \
+ static_assert (true, "") /* Require semicolon after. */
+#define DEFINE_NULL_INSTANCE(Type) \
+ const Type _hb_Null_##Type
+
+/* Global writable pool. Enlarge as necessary. */
+
+/* To be fully correct, CrapPool must be thread_local. However, we do not rely on CrapPool
+ * for correct operation. It only exist to catch and divert program logic bugs instead of
+ * causing bad memory access. So, races there are not actually introducing incorrectness
+ * in the code. Has ~12kb binary size overhead to have it, also clang build fails with it. */
+extern HB_INTERNAL
+/*thread_local*/ uint64_t _hb_CrapPool[(HB_NULL_POOL_SIZE + sizeof (uint64_t) - 1) / sizeof (uint64_t)];
+
+/* CRAP pool: Common Region for Access Protection. */
+template <typename Type>
+static inline Type& Crap () {
+ static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
+ Type *obj = reinterpret_cast<Type *> (_hb_CrapPool);
+ memcpy (obj, std::addressof (Null (Type)), sizeof (*obj));
+ return *obj;
+}
+template <typename QType>
+struct CrapHelper
+{
+ typedef hb_remove_const<hb_remove_reference<QType>> Type;
+ static Type & get_crap () { return Crap<Type> (); }
+};
+#define Crap(Type) CrapHelper<Type>::get_crap ()
+
+template <typename Type>
+struct CrapOrNullHelper {
+ static Type & get () { return Crap (Type); }
+};
+template <typename Type>
+struct CrapOrNullHelper<const Type> {
+ static const Type & get () { return Null (Type); }
+};
+#define CrapOrNull(Type) CrapOrNullHelper<Type>::get ()
+
+
+/*
+ * hb_nonnull_ptr_t
+ */
+
+template <typename P>
+struct hb_nonnull_ptr_t
+{
+ typedef hb_remove_pointer<P> T;
+
+ hb_nonnull_ptr_t (T *v_ = nullptr) : v (v_) {}
+ T * operator = (T *v_) { return v = v_; }
+ T * operator -> () const { return get (); }
+ T & operator * () const { return *get (); }
+ T ** operator & () const { return std::addressof (v); }
+ /* Only auto-cast to const types. */
+ template <typename C> operator const C * () const { return get (); }
+ operator const char * () const { return (const char *) get (); }
+ T * get () const { return v ? v : const_cast<T *> (std::addressof (Null (T))); }
+ T * get_raw () const { return v; }
+
+ private:
+ T *v;
+};
+
+
+#endif /* HB_NULL_HH */