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 the larger
43 * of sizeof(T) and T::null_size, otherwise return sizeof(T).
44 *
45 * The main purpose of this is to let structs communicate that they are not nullable,
46 * by defining min_size but *not* null_size. */
47
48 /* The hard way...
49 * https://stackoverflow.com/questions/7776448/sfinae-tried-with-bool-gives-compiler-error-template-argument-tvalue-invol
50 */
51
52 template <typename T, typename>
53 struct _hb_null_size : hb_integral_constant<unsigned, sizeof (T)> {};
54 template <typename T>
55 struct _hb_null_size<T, hb_void_t<decltype (T::min_size)>>
56 : hb_integral_constant<unsigned,
57 (sizeof (T) > T::null_size ? sizeof (T) : T::null_size)> {};
58 template <typename T>
59 using hb_null_size = _hb_null_size<T, void>;
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>
68 struct _hb_static_size : hb_integral_constant<unsigned, sizeof (T)> {};
69 template <typename T>
70 struct _hb_static_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::static_size> {};
71 template <typename T>
72 using hb_static_size = _hb_static_size<T, void>;
73 #define hb_static_size(T) hb_static_size<T>::value
74
75 template <typename T, typename>
76 struct _hb_min_size : hb_integral_constant<unsigned, sizeof (T)> {};
77 template <typename T>
78 struct _hb_min_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::min_size> {};
79 template <typename T>
80 using hb_min_size = _hb_min_size<T, void>;
81 #define hb_min_size(T) hb_min_size<T>::value
82
83
84 /*
85 * Null()
86 */
87
88 extern HB_INTERNAL
89 uint64_t const _hb_NullPool[(HB_NULL_POOL_SIZE + sizeof (uint64_t) - 1) / sizeof (uint64_t)];
90
91 /* Generic nul-content Null objects. */
92 template <typename Type>
93 struct Null {
get_nullNull94 static Type const & get_null ()
95 {
96 static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
97 return *reinterpret_cast<Type const *> (_hb_NullPool);
98 }
99 };
100 template <typename QType>
101 struct NullHelper
102 {
103 typedef hb_remove_const<hb_remove_reference<QType>> Type;
get_nullNullHelper104 static const Type & get_null () { return Null<Type>::get_null (); }
105 };
106 #define Null(Type) NullHelper<Type>::get_null ()
107
108 /* Specializations for arbitrary-content Null objects expressed in bytes. */
109 #define DECLARE_NULL_NAMESPACE_BYTES(Namespace, Type) \
110 } /* Close namespace. */ \
111 extern HB_INTERNAL const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::null_size]; \
112 template <> \
113 struct Null<Namespace::Type> { \
114 static Namespace::Type const & get_null () { \
115 return *reinterpret_cast<const Namespace::Type *> (_hb_Null_##Namespace##_##Type); \
116 } \
117 }; \
118 namespace Namespace { \
119 static_assert (true, "") /* Require semicolon after. */
120 #define DEFINE_NULL_NAMESPACE_BYTES(Namespace, Type) \
121 const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::null_size]
122
123 /* Specializations for arbitrary-content Null objects expressed as struct initializer. */
124 #define DECLARE_NULL_INSTANCE(Type) \
125 extern HB_INTERNAL const Type _hb_Null_##Type; \
126 template <> \
127 struct Null<Type> { \
128 static Type const & get_null () { \
129 return _hb_Null_##Type; \
130 } \
131 }; \
132 static_assert (true, "") /* Require semicolon after. */
133 #define DEFINE_NULL_INSTANCE(Type) \
134 const Type _hb_Null_##Type
135
136 /* Global writable pool. Enlarge as necessary. */
137
138 /* To be fully correct, CrapPool must be thread_local. However, we do not rely on CrapPool
139 * for correct operation. It only exist to catch and divert program logic bugs instead of
140 * causing bad memory access. So, races there are not actually introducing incorrectness
141 * in the code. Has ~12kb binary size overhead to have it, also clang build fails with it. */
142 extern HB_INTERNAL
143 /*thread_local*/ uint64_t _hb_CrapPool[(HB_NULL_POOL_SIZE + sizeof (uint64_t) - 1) / sizeof (uint64_t)];
144
145 /* CRAP pool: Common Region for Access Protection. */
146 template <typename Type>
Crap()147 static inline Type& Crap () {
148 static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
149 Type *obj = reinterpret_cast<Type *> (_hb_CrapPool);
150 memcpy (obj, &Null (Type), sizeof (*obj));
151 return *obj;
152 }
153 template <typename QType>
154 struct CrapHelper
155 {
156 typedef hb_remove_const<hb_remove_reference<QType>> Type;
get_crapCrapHelper157 static Type & get_crap () { return Crap<Type> (); }
158 };
159 #define Crap(Type) CrapHelper<Type>::get_crap ()
160
161 template <typename Type>
162 struct CrapOrNullHelper {
getCrapOrNullHelper163 static Type & get () { return Crap (Type); }
164 };
165 template <typename Type>
166 struct CrapOrNullHelper<const Type> {
getCrapOrNullHelper167 static const Type & get () { return Null (Type); }
168 };
169 #define CrapOrNull(Type) CrapOrNullHelper<Type>::get ()
170
171
172 /*
173 * hb_nonnull_ptr_t
174 */
175
176 template <typename P>
177 struct hb_nonnull_ptr_t
178 {
179 typedef hb_remove_pointer<P> T;
180
hb_nonnull_ptr_thb_nonnull_ptr_t181 hb_nonnull_ptr_t (T *v_ = nullptr) : v (v_) {}
operator =hb_nonnull_ptr_t182 T * operator = (T *v_) { return v = v_; }
operator ->hb_nonnull_ptr_t183 T * operator -> () const { return get (); }
operator *hb_nonnull_ptr_t184 T & operator * () const { return *get (); }
operator &hb_nonnull_ptr_t185 T ** operator & () const { return &v; }
186 /* Only auto-cast to const types. */
operator const C*hb_nonnull_ptr_t187 template <typename C> operator const C * () const { return get (); }
operator const char*hb_nonnull_ptr_t188 operator const char * () const { return (const char *) get (); }
gethb_nonnull_ptr_t189 T * get () const { return v ? v : const_cast<T *> (&Null (T)); }
get_rawhb_nonnull_ptr_t190 T * get_raw () const { return v; }
191
192 private:
193 T *v;
194 };
195
196
197 #endif /* HB_NULL_HH */
198