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111
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1 /* objc-map.h -- Implementation of map data structures for ObjC compiler
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2 Copyright (C) 2011-2017 Free Software Foundation, Inc.
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3 Written by Nicola Pero <nicola.pero@meta-innovation.com>
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4
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5 This program is free software; you can redistribute it and/or modify it
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6 under the terms of the GNU Lesser Public License as published by the
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7 Free Software Foundation; either version 3, or (at your option) any
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8 later version.
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9
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10 This program is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 GNU Lesser Public License for more details.
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14
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15 You should have received a copy of the GNU Lesser Public License
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16 along with this program; if not, write to the Free Software
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17 Foundation, 51 Franklin Street - Fifth Floor,
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18 Boston, MA 02110-1301, USA. */
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19
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20 #ifndef OBJC_MAP_H
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21 #define OBJC_MAP_H
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22
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23 /* A map is a data structure that maps a key to a value. In this file
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24 we currently have maps that can map a GCC identifier (a tree) to
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25 some other GCC tree. This is what the ObjC frontend mostly needs:
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26 being able to look up an identifier into an ObjC data structure. A
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27 typical usage is mapping ObjC class names (as identifiers) to a
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28 tree representing the class.
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29
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30 This implementation is fast. :-) */
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31
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32 /**
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33 ** Private definitions.
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34 **/
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35
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36 /* We include private declaration and definitions that are required to
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37 provide the implementation of inline functions. You should ignore
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38 these definitions (and the implementation of the inline functions)
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39 as they are not part of the public API and may change. */
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40 typedef unsigned int objc_map_private_hash_t;
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41
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42 /* This is used as sentinel. */
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43 #define OBJC_MAP_PRIVATE_EMPTY_SLOT (tree)0
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44
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45 struct GTY(()) objc_map_private {
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46 /* Total number of slots. This is the maximum number of elements
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47 that can be currently stored in the map before resizing. This is
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48 the number of slots in the C array. Important: this is
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49 guaranteed to be a power of 2. When we create (or resize) the
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50 map, we round up the size to the next power of 2. This allows us
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51 to convert a hash to a position in the hashtable by simply doing
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52 "position = hash & mask", where mask is number_of_slots - 1
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53 instead of using a modulo (which requires a division). */
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54 size_t number_of_slots;
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55
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56 /* This is number_of_slots - 1, precomputed. */
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57 size_t mask;
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58
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59 /* Number of slots that are not empty (ie, that are active). We
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60 keep counts using this variable which can easily be checked
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61 against max_number_of_non_empty_slots. */
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62 size_t number_of_non_empty_slots;
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63
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64 /* This is the load factor limit. When the number of non empty
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65 slots equals this number, we need to resize the array. This is
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66 calculated once, when the slots are resized, and then kept cached
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67 so it can be compared quickly when elements are added. */
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68 size_t max_number_of_non_empty_slots;
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69
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70 /* The maximum load factor. */
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71 int maximum_load_factor;
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72
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73 /* These are the keys. */
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74 tree * GTY ((length ("%h.number_of_slots"))) slots;
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75
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76 /* These are the values. values[i] is the value corresponding
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77 to slots[i]. */
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78 tree * GTY ((length ("%h.number_of_slots"))) values;
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79 };
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80
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81 /* Private functions used to resize the map. They may be called by
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82 the inline functions when adding elements. */
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83 extern void
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84 objc_map_private_grow (struct objc_map_private *map);
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85
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86
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87 /**
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88 ** The definition of a map.
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89 **/
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90 typedef struct objc_map_private *objc_map_t;
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91
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92
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93 /**
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94 ** Creating a map.
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95 **/
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96
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97 /* objc_map_alloc_ggc() creates a new map which is under GGC. The initial
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98 capacity must be specified as an argument; this is used to size the map
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99 when it is created. */
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100 objc_map_t objc_map_alloc_ggc (size_t initial_capacity);
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101
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102 /**
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103 ** Performance tuning.
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104 **/
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105
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106 /* Set a maximum load factor for the data structure. This is the main
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107 tuning parameter to improve performance (at the expense of
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108 memory). */
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109 void objc_map_set_maximum_load_factor (objc_map_t map, int number_between_zero_and_one_hundred);
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110
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111 /* Read the maximum load factor. */
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112 int objc_map_maximum_load_factor (objc_map_t map);
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113
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114
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115 /**
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116 ** Getting the value corresponding to a key.
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117 **/
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118
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119 /* This is the value returned by objc_map_get() when the value
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120 corresponding to a key is not found. */
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121 #define OBJC_MAP_NOT_FOUND (tree)1
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122
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123 /* objc_map_get() returns the value associated with a certain key,
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124 or OBJC_MAP_NOT_FOUND if there is no value associated with that key.
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125 Note that you can also use it to simply check if the map contains a
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126 pair with a certain key; just compare the result of calling
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127 objc_map_get() to OBJC_MAP_NOT_FOUND.
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128
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129 It is essential to always check the results of the call to make
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130 sure it is not OBJC_MAP_NOT_FOUND.
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131
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132 NULL is a valid value, so a key can be inserted into a map with
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133 value NULL, and objc_map_get() will return NULL in that case.
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134 So a result of NULL means that they key *was* found, and the value
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135 associated with it was NULL. */
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136 static inline tree
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137 objc_map_get (objc_map_t map, /* struct tree_identifier * */tree key)
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138 {
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139 /* The inline implementation is private and may change without notice. */
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140 objc_map_private_hash_t hash = IDENTIFIER_HASH_VALUE (key);
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141 size_t i = hash & map->mask;
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142 size_t j = 1;
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143
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144 if (map->slots[i] == OBJC_MAP_PRIVATE_EMPTY_SLOT)
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145 return OBJC_MAP_NOT_FOUND;
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146
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147 if (map->slots[i] == key)
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148 return map->values[i];
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149
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150 while (1)
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151 {
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152 i = (i + j) & map->mask;
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153
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154 if (map->slots[i] == OBJC_MAP_PRIVATE_EMPTY_SLOT)
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155 return OBJC_MAP_NOT_FOUND;
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156
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157 if (map->slots[i] == key)
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158 return map->values[i];
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159
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160 j++;
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161 }
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162 }
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163
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164 /* objc_map_put() puts a key/value pair into the map. If the map does
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165 not contain the key, it is added to it with the specified value.
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166 If the map already contains the key, the previous value is replaced
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167 with the new one.
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168
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169 You can use any identifier as key, with the exception of NULL.
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170
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171 You can use any tree as value, including NULL. */
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172 static inline
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173 void objc_map_put (objc_map_t map, /*struct tree_identifier * */tree key, tree value)
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174 {
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175 /* The inline implementation is private and may change without notice. */
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176 objc_map_private_hash_t hash = IDENTIFIER_HASH_VALUE (key);
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177 size_t i, j = 0;
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178
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179 if (map->number_of_non_empty_slots == map->max_number_of_non_empty_slots)
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180 objc_map_private_grow (map);
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181
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182 i = hash & map->mask;
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183
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184 while (1)
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185 {
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186 if (map->slots[i] == OBJC_MAP_PRIVATE_EMPTY_SLOT)
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187 {
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188 map->number_of_non_empty_slots++;
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189 map->slots[i] = key;
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190 map->values[i] = value;
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191 return;
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192 }
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193 if (map->slots[i] == key)
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194 {
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195 map->values[i] = value;
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196 return;
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197 }
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198
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199 j++;
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200 i = (i + j) & map->mask;
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201 }
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202 }
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203
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204 /**
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205 ** Iterating over a map using an iterator.
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206 **/
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207
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208 /* When using iterators you can iterate directly on the elements in
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209 the map, and take an action over each one.
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210
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211 Here is how you iterate over a hmap_pointer using iterators:
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212
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213 objc_map_iterator_t i;
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214
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215 objc_map_iterator_initialize (map, &i);
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216
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217 while (objc_map_iterator_move_to_next (map, &i))
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218 {
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219 tree p = objc_map_iterator_current_key (map, i);
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220 tree q = objc_map_iterator_current_value (map, i);
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221
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222 ... do something with p and q ...
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223 }
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224
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225 You'll notice that the functions that modify the iterator (to
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226 initialize it, or move it to the next element) take a pointer to it
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227 as argument (as in "&i"), while the functions that only read its
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228 state (to read the current key/value, or remove the current
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229 key/value from the map) take it as a direct argument (as in "i").
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230
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231 Note that all the objc_map_iterator_*() functions are inline and if
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232 you follow the pattern above, the compiler should be able to inline
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233 everything into a very efficient loop, roughly equivalent to
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234 hand-writing a C loop that iterates directly onto the hmap_pointer
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235 internal data structures. */
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236
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237 /* A objc_map_iterator_t variable encapsulates the state of an
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238 iteration. The fact that this is actually a size_t (pointing to
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239 the index of the slot that we return next) is an internal, private
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240 detail of the implementation and may change without notice. */
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241 typedef size_t objc_map_iterator_t;
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242
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243 /* Initialize an iterator to iterate over the specified objc_map. You
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244 must use this before starting the iteration, to get a working
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245 iterator. */
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246 static inline
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247 void
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248 objc_map_iterator_initialize (objc_map_t map ATTRIBUTE_UNUSED, objc_map_iterator_t *i)
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249 {
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250 /* The inline implementation is private and may change without notice. */
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251 /* This is trivial, but the same API would work to initialize more
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252 complicated iterators. */
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253 *i = 0;
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254 }
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255
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256 #define OBJC_MAP_FAILURE 0
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257 #define OBJC_MAP_SUCCESS 1
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258
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259 /* Move the iterator to the next key/value pair, and return
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260 OBJC_MAP_SUCCESS if there is such a key/value pair, and
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261 OBJC_MAP_FAILURE if there are no more ones. The iterator must have
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262 been initialized using objc_map_iterator_initialize(). Note that
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263 because this function is modifying the iterator, you need to pass a
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264 pointer to it. */
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265 static inline
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266 int
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267 objc_map_iterator_move_to_next (objc_map_t map, objc_map_iterator_t *i)
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268 {
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269 /* The inline implementation is private and may change without notice. */
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270 while (1)
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271 {
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272 void *slot;
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273 if (*i == map->number_of_slots)
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274 return OBJC_MAP_FAILURE;
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275
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276 slot = map->slots[*i];
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277 *i = *i + 1;
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278 if (slot != OBJC_MAP_PRIVATE_EMPTY_SLOT)
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279 return OBJC_MAP_SUCCESS;
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280 }
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281 }
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282
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283 /* Return the current key. You can only call it after you have called
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284 objc_map_iterator_move_to_next() at least once (to move to the
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285 first element), and only if the last call returned
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286 OBJC_MAP_SUCCESS. The behavior is otherwise undefined, probably a
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287 segmentation fault. */
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288 static inline
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289 tree
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290 objc_map_iterator_current_key (objc_map_t map, objc_map_iterator_t i)
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291 {
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292 /* The inline implementation is private and may change without notice. */
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293 return map->slots[i - 1];
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294 }
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295
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296 /* Return the current value. You can only call it after you have
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297 called objc_map_iterator_move_to_next() at least once (to move to
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298 the first element), and only if the last call returned
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299 OBJC_MAP_SUCCESS. The behavior is otherwise undefined, probably a
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300 segmentation fault. */
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301 static inline
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302 tree
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303 objc_map_iterator_current_value (objc_map_t map, objc_map_iterator_t i)
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304 {
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305 /* The inline implementation is private and may change without notice. */
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306 return map->values[i - 1];
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307 }
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308
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309 #endif /* OBJC_MAP_H */
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