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kc3-lang/harfbuzz/src/hb-null.hh
Behdad Esfahbod
- src/hb-null.hh
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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 448 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::min_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, &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 &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 *> (&Null (T)); } T * get_raw () const { return v; } private: T *v; }; #endif /* HB_NULL_HH */