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 86 { 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)> > 89 { 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)> > 92 { static inline void value (T &o, const T v) { o = v; } }; 93 94 template <typename T, typename 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> 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; 116 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> 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; 165 static Type & get_crap () { return Crap<Type> (); } 166 }; 167 #define Crap(Type) CrapHelper<Type>::get_crap () 168 169 template <typename Type> 170 struct CrapOrNullHelper { 171 static Type & get () { return Crap(Type); } 172 }; 173 template <typename Type> 174 struct CrapOrNullHelper<const Type> { 175 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; 188 189 hb_nonnull_ptr_t (T *v_ = nullptr) : v (v_) {} 190 T * operator = (T *v_) { return v = v_; } 191 T * operator -> () const { return get (); } 192 T & operator * () const { return *get (); } 193 T ** operator & () const { return &v; } 194 /* Only auto-cast to const types. */ 195 template <typename C> operator const C * () const { return get (); } 196 operator const char * () const { return (const char *) get (); } 197 T * get () const { return v ? v : const_cast<T *> (&Null(T)); } 198 T * get_raw () const { return v; } 199 200 T *v; 201 }; 202 203 204 #endif /* HB_NULL_HH */ 205
