198 lines
6.6 KiB
C++
198 lines
6.6 KiB
C++
/*
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* Copyright © 2018 Google, Inc.
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*
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* This is part of HarfBuzz, a text shaping library.
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*
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* Permission is hereby granted, without written agreement and without
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* license or royalty fees, to use, copy, modify, and distribute this
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* software and its documentation for any purpose, provided that the
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* above copyright notice and the following two paragraphs appear in
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* all copies of this software.
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*
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* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
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* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
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* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
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* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*
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* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
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* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
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* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
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* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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*
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* Google Author(s): Behdad Esfahbod
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*/
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#ifndef HB_NULL_HH
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#define HB_NULL_HH
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#include "hb.hh"
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#include "hb-meta.hh"
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/*
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* Static pools
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*/
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/* Global nul-content Null pool. Enlarge as necessary. */
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#define HB_NULL_POOL_SIZE 384
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/* Use SFINAE to sniff whether T has min_size; in which case return the larger
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* of sizeof(T) and T::null_size, otherwise return sizeof(T).
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*
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* The main purpose of this is to let structs communicate that they are not nullable,
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* by defining min_size but *not* null_size. */
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/* The hard way...
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* https://stackoverflow.com/questions/7776448/sfinae-tried-with-bool-gives-compiler-error-template-argument-tvalue-invol
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*/
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template <typename T, typename>
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struct _hb_null_size : hb_integral_constant<unsigned, sizeof (T)> {};
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template <typename T>
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struct _hb_null_size<T, hb_void_t<decltype (T::min_size)>>
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: hb_integral_constant<unsigned,
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(sizeof (T) > T::null_size ? sizeof (T) : T::null_size)> {};
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template <typename T>
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using hb_null_size = _hb_null_size<T, void>;
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#define hb_null_size(T) hb_null_size<T>::value
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/* These doesn't belong here, but since is copy/paste from above, put it here. */
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/* hb_static_size (T)
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* Returns T::static_size if T::min_size is defined, or sizeof (T) otherwise. */
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template <typename T, typename>
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struct _hb_static_size : hb_integral_constant<unsigned, sizeof (T)> {};
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template <typename T>
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struct _hb_static_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::static_size> {};
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template <typename T>
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using hb_static_size = _hb_static_size<T, void>;
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#define hb_static_size(T) hb_static_size<T>::value
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template <typename T, typename>
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struct _hb_min_size : hb_integral_constant<unsigned, sizeof (T)> {};
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template <typename T>
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struct _hb_min_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::min_size> {};
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template <typename T>
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using hb_min_size = _hb_min_size<T, void>;
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#define hb_min_size(T) hb_min_size<T>::value
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/*
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* Null()
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*/
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extern HB_INTERNAL
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uint64_t const _hb_NullPool[(HB_NULL_POOL_SIZE + sizeof (uint64_t) - 1) / sizeof (uint64_t)];
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/* Generic nul-content Null objects. */
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template <typename Type>
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struct Null {
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static Type const & get_null ()
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{
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static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
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return *reinterpret_cast<Type const *> (_hb_NullPool);
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}
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};
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template <typename QType>
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struct NullHelper
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{
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typedef hb_remove_const<hb_remove_reference<QType>> Type;
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static const Type & get_null () { return Null<Type>::get_null (); }
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};
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#define Null(Type) NullHelper<Type>::get_null ()
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/* Specializations for arbitrary-content Null objects expressed in bytes. */
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#define DECLARE_NULL_NAMESPACE_BYTES(Namespace, Type) \
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} /* Close namespace. */ \
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extern HB_INTERNAL const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::null_size]; \
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template <> \
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struct Null<Namespace::Type> { \
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static Namespace::Type const & get_null () { \
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return *reinterpret_cast<const Namespace::Type *> (_hb_Null_##Namespace##_##Type); \
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} \
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}; \
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namespace Namespace { \
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static_assert (true, "") /* Require semicolon after. */
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#define DEFINE_NULL_NAMESPACE_BYTES(Namespace, Type) \
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const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::null_size]
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/* Specializations for arbitrary-content Null objects expressed as struct initializer. */
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#define DECLARE_NULL_INSTANCE(Type) \
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extern HB_INTERNAL const Type _hb_Null_##Type; \
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template <> \
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struct Null<Type> { \
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static Type const & get_null () { \
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return _hb_Null_##Type; \
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} \
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}; \
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static_assert (true, "") /* Require semicolon after. */
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#define DEFINE_NULL_INSTANCE(Type) \
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const Type _hb_Null_##Type
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/* Global writable pool. Enlarge as necessary. */
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/* To be fully correct, CrapPool must be thread_local. However, we do not rely on CrapPool
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* for correct operation. It only exist to catch and divert program logic bugs instead of
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* causing bad memory access. So, races there are not actually introducing incorrectness
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* in the code. Has ~12kb binary size overhead to have it, also clang build fails with it. */
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extern HB_INTERNAL
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/*thread_local*/ uint64_t _hb_CrapPool[(HB_NULL_POOL_SIZE + sizeof (uint64_t) - 1) / sizeof (uint64_t)];
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/* CRAP pool: Common Region for Access Protection. */
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template <typename Type>
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static inline Type& Crap () {
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static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
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Type *obj = reinterpret_cast<Type *> (_hb_CrapPool);
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memcpy (obj, &Null (Type), sizeof (*obj));
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return *obj;
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}
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template <typename QType>
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struct CrapHelper
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{
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typedef hb_remove_const<hb_remove_reference<QType>> Type;
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static Type & get_crap () { return Crap<Type> (); }
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};
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#define Crap(Type) CrapHelper<Type>::get_crap ()
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template <typename Type>
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struct CrapOrNullHelper {
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static Type & get () { return Crap (Type); }
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};
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template <typename Type>
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struct CrapOrNullHelper<const Type> {
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static const Type & get () { return Null (Type); }
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};
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#define CrapOrNull(Type) CrapOrNullHelper<Type>::get ()
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/*
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* hb_nonnull_ptr_t
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*/
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template <typename P>
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struct hb_nonnull_ptr_t
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{
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typedef hb_remove_pointer<P> T;
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hb_nonnull_ptr_t (T *v_ = nullptr) : v (v_) {}
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T * operator = (T *v_) { return v = v_; }
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T * operator -> () const { return get (); }
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T & operator * () const { return *get (); }
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T ** operator & () const { return &v; }
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/* Only auto-cast to const types. */
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template <typename C> operator const C * () const { return get (); }
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operator const char * () const { return (const char *) get (); }
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T * get () const { return v ? v : const_cast<T *> (&Null (T)); }
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T * get_raw () const { return v; }
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private:
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T *v;
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};
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#endif /* HB_NULL_HH */
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