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1 /*
2  * Copyright © 2018  Google, Inc.
3  *
4  *  This is part of HarfBuzz, a text shaping library.
5  *
6  * Permission is hereby granted, without written agreement and without
7  * license or royalty fees, to use, copy, modify, and distribute this
8  * software and its documentation for any purpose, provided that the
9  * above copyright notice and the following two paragraphs appear in
10  * all copies of this software.
11  *
12  * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
13  * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
14  * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
15  * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
16  * DAMAGE.
17  *
18  * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
19  * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
20  * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
21  * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
22  * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
23  *
24  * Google Author(s): Behdad Esfahbod
25  */
26 
27 #ifndef HB_NULL_HH
28 #define HB_NULL_HH
29 
30 #include "hb.hh"
31 
32 
33 /*
34  * Static pools
35  */
36 
37 /* Global nul-content Null pool.  Enlarge as necessary. */
38 
39 #define HB_NULL_POOL_SIZE 9880
40 
41 /* Use SFINAE to sniff whether T has min_size; in which case return T::null_size,
42  * otherwise return sizeof(T). */
43 
44 /* The hard way...
45  * https://stackoverflow.com/questions/7776448/sfinae-tried-with-bool-gives-compiler-error-template-argument-tvalue-invol
46  */
47 
48 template<bool> struct _hb_bool_type {};
49 
50 template <typename T, typename B>
51 struct _hb_null_size
52 { enum { value = sizeof (T) }; };
53 template <typename T>
54 struct _hb_null_size<T, _hb_bool_type<(bool) (1 + (unsigned int) T::min_size)> >
55 { enum { value = T::null_size }; };
56 
57 template <typename T>
58 struct hb_null_size
59 { enum { value = _hb_null_size<T, _hb_bool_type<true> >::value }; };
60 #define hb_null_size(T) hb_null_size<T>::value
61 
62 /* These doesn't belong here, but since is copy/paste from above, put it here. */
63 
64 /* hb_static_size (T)
65  * Returns T::static_size if T::min_size is defined, or sizeof (T) otherwise. */
66 
67 template <typename T, typename B>
68 struct _hb_static_size
69 { enum { value = sizeof (T) }; };
70 template <typename T>
71 struct _hb_static_size<T, _hb_bool_type<(bool) (1 + (unsigned int) T::min_size)> >
72 { enum { value = T::static_size }; };
73 
74 template <typename T>
75 struct hb_static_size
76 { enum { value = _hb_static_size<T, _hb_bool_type<true> >::value }; };
77 #define hb_static_size(T) hb_static_size<T>::value
78 
79 
80 /* hb_assign (obj, value)
81  * Calls obj.set (value) if obj.min_size is defined and value has different type
82  * from obj, or obj = v otherwise. */
83 
84 template <typename T, typename V, typename B>
85 struct _hb_assign
value_hb_assign86 { static inline void value (T &o, const V v) { o = v; } };
87 template <typename T, typename V>
88 struct _hb_assign<T, V, _hb_bool_type<(bool) (1 + (unsigned int) T::min_size)> >
value_hb_assign89 { static inline void value (T &o, const V v) { o.set (v); } };
90 template <typename T>
91 struct _hb_assign<T, T, _hb_bool_type<(bool) (1 + (unsigned int) T::min_size)> >
value_hb_assign92 { static inline void value (T &o, const T v) { o = v; } };
93 
94 template <typename T, typename V>
hb_assign(T & o,const V v)95 static inline void hb_assign (T &o, const V v)
96 { _hb_assign<T, V, _hb_bool_type<true> >::value (o, v); };
97 
98 
99 /*
100  * Null()
101  */
102 
103 extern HB_INTERNAL
104 hb_vector_size_impl_t const _hb_NullPool[(HB_NULL_POOL_SIZE + sizeof (hb_vector_size_impl_t) - 1) / sizeof (hb_vector_size_impl_t)];
105 
106 /* Generic nul-content Null objects. */
107 template <typename Type>
Null()108 static inline Type const & Null () {
109   static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
110   return *reinterpret_cast<Type const *> (_hb_NullPool);
111 }
112 template <typename QType>
113 struct NullHelper
114 {
115   typedef typename hb_remove_const (typename hb_remove_reference (QType)) Type;
get_nullNullHelper116   static const Type & get_null () { return Null<Type> (); }
117 };
118 #define Null(Type) NullHelper<Type>::get_null ()
119 
120 /* Specializations for arbitrary-content Null objects expressed in bytes. */
121 #define DECLARE_NULL_NAMESPACE_BYTES(Namespace, Type) \
122 	} /* Close namespace. */ \
123 	extern HB_INTERNAL const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::null_size]; \
124 	template <> \
125 	/*static*/ inline const Namespace::Type& Null<Namespace::Type> () { \
126 	  return *reinterpret_cast<const Namespace::Type *> (_hb_Null_##Namespace##_##Type); \
127 	} \
128 	namespace Namespace { \
129 	static_assert (true, "Just so we take semicolon after.")
130 #define DEFINE_NULL_NAMESPACE_BYTES(Namespace, Type) \
131 	const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::null_size]
132 
133 /* Specializations for arbitrary-content Null objects expressed as struct initializer. */
134 #define DECLARE_NULL_INSTANCE(Type) \
135 	extern HB_INTERNAL const Type _hb_Null_##Type; \
136 	template <> \
137 	/*static*/ inline const Type& Null<Type> () { \
138 	  return _hb_Null_##Type; \
139 	} \
140 static_assert (true, "Just so we take semicolon after.")
141 #define DEFINE_NULL_INSTANCE(Type) \
142 	const Type _hb_Null_##Type
143 
144 /* Global writable pool.  Enlarge as necessary. */
145 
146 /* To be fully correct, CrapPool must be thread_local. However, we do not rely on CrapPool
147  * for correct operation. It only exist to catch and divert program logic bugs instead of
148  * causing bad memory access. So, races there are not actually introducing incorrectness
149  * in the code. Has ~12kb binary size overhead to have it, also clang build fails with it. */
150 extern HB_INTERNAL
151 /*thread_local*/ hb_vector_size_impl_t _hb_CrapPool[(HB_NULL_POOL_SIZE + sizeof (hb_vector_size_impl_t) - 1) / sizeof (hb_vector_size_impl_t)];
152 
153 /* CRAP pool: Common Region for Access Protection. */
154 template <typename Type>
Crap()155 static inline Type& Crap () {
156   static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
157   Type *obj = reinterpret_cast<Type *> (_hb_CrapPool);
158   memcpy (obj, &Null(Type), sizeof (*obj));
159   return *obj;
160 }
161 template <typename QType>
162 struct CrapHelper
163 {
164   typedef typename hb_remove_const (typename hb_remove_reference (QType)) Type;
get_crapCrapHelper165   static Type & get_crap () { return Crap<Type> (); }
166 };
167 #define Crap(Type) CrapHelper<Type>::get_crap ()
168 
169 template <typename Type>
170 struct CrapOrNullHelper {
getCrapOrNullHelper171   static Type & get () { return Crap(Type); }
172 };
173 template <typename Type>
174 struct CrapOrNullHelper<const Type> {
getCrapOrNullHelper175   static const Type & get () { return Null(Type); }
176 };
177 #define CrapOrNull(Type) CrapOrNullHelper<Type>::get ()
178 
179 
180 /*
181  * hb_nonnull_ptr_t
182  */
183 
184 template <typename P>
185 struct hb_nonnull_ptr_t
186 {
187   typedef typename hb_remove_pointer (P) T;
188 
hb_nonnull_ptr_thb_nonnull_ptr_t189   hb_nonnull_ptr_t (T *v_ = nullptr) : v (v_) {}
operator =hb_nonnull_ptr_t190   T * operator = (T *v_)   { return v = v_; }
operator ->hb_nonnull_ptr_t191   T * operator -> () const { return get (); }
operator *hb_nonnull_ptr_t192   T & operator * () const  { return *get (); }
operator &hb_nonnull_ptr_t193   T ** operator & () const { return &v; }
194   /* Only auto-cast to const types. */
operator const C*hb_nonnull_ptr_t195   template <typename C> operator const C * () const { return get (); }
operator const char*hb_nonnull_ptr_t196   operator const char * () const { return (const char *) get (); }
gethb_nonnull_ptr_t197   T * get () const { return v ? v : const_cast<T *> (&Null(T)); }
get_rawhb_nonnull_ptr_t198   T * get_raw () const { return v; }
199 
200   T *v;
201 };
202 
203 
204 #endif /* HB_NULL_HH */
205