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
49template <typename T, typename>
50struct _hb_null_size : hb_integral_constant<unsigned, sizeof (T)> {};
51template <typename T>
52struct _hb_null_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::null_size> {};
53
54template <typename T>
55using hb_null_size = _hb_null_size<T, void>;
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
63template <typename T, typename>
64struct _hb_static_size : hb_integral_constant<unsigned, sizeof (T)> {};
65template <typename T>
66struct _hb_static_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::static_size> {};
67template <typename T>
68using hb_static_size = _hb_static_size<T, void>;
69#define hb_static_size(T) hb_static_size<T>::value
70
71
72/*
73 * Null()
74 */
75
76extern HB_INTERNAL
77uint64_t const _hb_NullPool[(HB_NULL_POOL_SIZE + sizeof (uint64_t) - 1) / sizeof (uint64_t)];
78
79/* Generic nul-content Null objects. */
80template <typename Type>
81struct 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};
88template <typename QType>
89struct NullHelper
90{
91 typedef hb_remove_const<hb_remove_reference<QType>> Type;
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, "Just so we take 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, "Just so we take 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. */
130extern 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. */
134template <typename Type>
135static 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}
141template <typename QType>
142struct CrapHelper
143{
144 typedef hb_remove_const<hb_remove_reference<QType>> Type;
145 static Type & get_crap () { return Crap<Type> (); }
146};
147#define Crap(Type) CrapHelper<Type>::get_crap ()
148
149template <typename Type>
150struct CrapOrNullHelper {
151 static Type & get () { return Crap(Type); }
152};
153template <typename Type>
154struct 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
164template <typename P>
165struct hb_nonnull_ptr_t
166{
167 typedef hb_remove_pointer<P> T;
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 T *v;
181};
182
183
184#endif /* HB_NULL_HH */
185