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