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hb-null.hh
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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 #include "hb-meta.hh"
32 
33 
34 /*
35  * Static pools
36  */
37 
38 /* Global nul-content Null pool. Enlarge as necessary. */
39 
40 #define HB_NULL_POOL_SIZE 384
41 
42 /* Use SFINAE to sniff whether T has min_size; in which case return T::null_size,
43  * otherwise return sizeof(T). */
44 
45 /* The hard way...
46  * https://stackoverflow.com/questions/7776448/sfinae-tried-with-bool-gives-compiler-error-template-argument-tvalue-invol
47  */
48 
49 template <typename T, typename>
50 struct _hb_null_size : hb_integral_constant<unsigned, sizeof (T)> {};
51 template <typename T>
52 struct _hb_null_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::null_size> {};
53 
54 template <typename T>
56 #define hb_null_size(T) hb_null_size<T>::value
57 
58 /* These doesn't belong here, but since is copy/paste from above, put it here. */
59 
60 /* hb_static_size (T)
61  * Returns T::static_size if T::min_size is defined, or sizeof (T) otherwise. */
62 
63 template <typename T, typename>
64 struct _hb_static_size : hb_integral_constant<unsigned, sizeof (T)> {};
65 template <typename T>
66 struct _hb_static_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::static_size> {};
67 template <typename T>
69 #define hb_static_size(T) hb_static_size<T>::value
70 
71 
72 /*
73  * Null()
74  */
75 
76 extern HB_INTERNAL
77 uint64_t const _hb_NullPool[(HB_NULL_POOL_SIZE + sizeof (uint64_t) - 1) / sizeof (uint64_t)];
78 
79 /* Generic nul-content Null objects. */
80 template <typename Type>
81 struct Null {
82  static Type const & get_null ()
83  {
84  static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
85  return *reinterpret_cast<Type const *> (_hb_NullPool);
86  }
87 };
88 template <typename QType>
89 struct NullHelper
90 {
92  static const Type & get_null () { return Null<Type>::get_null (); }
93 };
94 #define Null(Type) NullHelper<Type>::get_null ()
95 
96 /* Specializations for arbitrary-content Null objects expressed in bytes. */
97 #define DECLARE_NULL_NAMESPACE_BYTES(Namespace, Type) \
98  } /* Close namespace. */ \
99  extern HB_INTERNAL const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::null_size]; \
100  template <> \
101  struct Null<Namespace::Type> { \
102  static Namespace::Type const & get_null () { \
103  return *reinterpret_cast<const Namespace::Type *> (_hb_Null_##Namespace##_##Type); \
104  } \
105  }; \
106  namespace Namespace { \
107  static_assert (true, "") /* Require semicolon after. */
108 #define DEFINE_NULL_NAMESPACE_BYTES(Namespace, Type) \
109  const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::null_size]
110 
111 /* Specializations for arbitrary-content Null objects expressed as struct initializer. */
112 #define DECLARE_NULL_INSTANCE(Type) \
113  extern HB_INTERNAL const Type _hb_Null_##Type; \
114  template <> \
115  struct Null<Type> { \
116  static Type const & get_null () { \
117  return _hb_Null_##Type; \
118  } \
119  }; \
120  static_assert (true, "") /* Require semicolon after. */
121 #define DEFINE_NULL_INSTANCE(Type) \
122  const Type _hb_Null_##Type
123 
124 /* Global writable pool. Enlarge as necessary. */
125 
126 /* To be fully correct, CrapPool must be thread_local. However, we do not rely on CrapPool
127  * for correct operation. It only exist to catch and divert program logic bugs instead of
128  * causing bad memory access. So, races there are not actually introducing incorrectness
129  * in the code. Has ~12kb binary size overhead to have it, also clang build fails with it. */
130 extern HB_INTERNAL
131 /*thread_local*/ uint64_t _hb_CrapPool[(HB_NULL_POOL_SIZE + sizeof (uint64_t) - 1) / sizeof (uint64_t)];
132 
133 /* CRAP pool: Common Region for Access Protection. */
134 template <typename Type>
135 static inline Type& Crap () {
136  static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
137  Type *obj = reinterpret_cast<Type *> (_hb_CrapPool);
138  memcpy (obj, &Null (Type), sizeof (*obj));
139  return *obj;
140 }
141 template <typename QType>
143 {
145  static Type & get_crap () { return Crap<Type> (); }
146 };
147 #define Crap(Type) CrapHelper<Type>::get_crap ()
148 
149 template <typename Type>
151  static Type & get () { return Crap (Type); }
152 };
153 template <typename Type>
154 struct CrapOrNullHelper<const Type> {
155  static const Type & get () { return Null (Type); }
156 };
157 #define CrapOrNull(Type) CrapOrNullHelper<Type>::get ()
158 
159 
160 /*
161  * hb_nonnull_ptr_t
162  */
163 
164 template <typename P>
166 {
168 
169  hb_nonnull_ptr_t (T *v_ = nullptr) : v (v_) {}
170  T * operator = (T *v_) { return v = v_; }
171  T * operator -> () const { return get (); }
172  T & operator * () const { return *get (); }
173  T ** operator & () const { return &v; }
174  /* Only auto-cast to const types. */
175  template <typename C> operator const C * () const { return get (); }
176  operator const char * () const { return (const char *) get (); }
177  T * get () const { return v ? v : const_cast<T *> (&Null (T)); }
178  T * get_raw () const { return v; }
179 
180  private:
181  T *v;
182 };
183 
184 
185 #endif /* HB_NULL_HH */
#define C
Definition: afm2pl.c:546
#define static_assert(c, msg)
Definition: cff.cc:31
#define T
Definition: fmt.h:20
#define memcpy(d, s, n)
Definition: gsftopk.c:64
#define const
Definition: ftzconf.h:91
unsigned __int64 uint64_t
Definition: stdint.h:90
typename hb_match_pointer< T >::type hb_remove_pointer
Definition: hb-meta.hh:118
typename hb_match_const< T >::type hb_remove_const
Definition: hb-meta.hh:102
typename _hb_void_t< Ts... >::type hb_void_t
Definition: hb-meta.hh:42
#define Crap(Type)
Definition: hb-null.hh:147
#define Null(Type)
Definition: hb-null.hh:94
uint64_t const _hb_NullPool[(384+sizeof(uint64_t) - 1)/sizeof(uint64_t)]
Definition: hb-static.cc:42
#define HB_NULL_POOL_SIZE
Definition: hb-null.hh:40
uint64_t _hb_CrapPool[(384+sizeof(uint64_t) - 1)/sizeof(uint64_t)]
Definition: hb-static.cc:43
#define HB_INTERNAL
Definition: hb.hh:265
#define uint64_t
Definition: stdint.in.h:215
hb_remove_const< hb_remove_reference< QType > > Type
Definition: hb-null.hh:144
static Type & get_crap()
Definition: hb-null.hh:145
static const Type & get()
Definition: hb-null.hh:155
static Type & get()
Definition: hb-null.hh:151
static const Type & get_null()
Definition: hb-null.hh:92
hb_remove_const< hb_remove_reference< QType > > Type
Definition: hb-null.hh:91
Definition: hb-null.hh:81
static Type const & get_null()
Definition: hb-null.hh:82
hb_remove_pointer< P > T
Definition: hb-null.hh:167
T * operator->() const
Definition: hb-null.hh:171
T * get() const
Definition: hb-null.hh:177
T ** operator&() const
Definition: hb-null.hh:173
T & operator*() const
Definition: hb-null.hh:172
hb_nonnull_ptr_t(T *v_=nullptr)
Definition: hb-null.hh:169
T * operator=(T *v_)
Definition: hb-null.hh:170
T * get_raw() const
Definition: hb-null.hh:178