1 | /* |
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2 | * Copyright (c) 2010 Gedare Bloom. |
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3 | * |
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4 | * The license and distribution terms for this file may be |
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5 | * found in the file LICENSE in this distribution or at |
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6 | * http://www.rtems.com/license/LICENSE. |
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7 | */ |
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8 | |
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9 | #if HAVE_CONFIG_H |
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10 | #include "config.h" |
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11 | #endif |
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12 | |
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13 | #include <rtems/score/rbtreeimpl.h> |
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14 | #include <rtems/score/isr.h> |
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15 | |
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16 | /** @brief Validate and fix-up tree properties after deleting a node |
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17 | * |
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18 | * This routine is called on a black node, @a the_node, after its deletion. |
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19 | * This function maintains the properties of the red-black tree. |
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20 | * |
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21 | * @note It does NOT disable interrupts to ensure the atomicity |
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22 | * of the extract operation. |
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23 | */ |
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24 | static void _RBTree_Extract_validate_unprotected( |
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25 | RBTree_Node *the_node |
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26 | ) |
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27 | { |
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28 | RBTree_Node *parent, *sibling; |
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29 | RBTree_Direction dir; |
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30 | |
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31 | parent = the_node->parent; |
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32 | if(!parent->parent) return; |
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33 | |
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34 | sibling = _RBTree_Sibling(the_node); |
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35 | |
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36 | /* continue to correct tree as long as the_node is black and not the root */ |
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37 | while (!_RBTree_Is_red(the_node) && parent->parent) { |
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38 | |
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39 | /* if sibling is red, switch parent (black) and sibling colors, |
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40 | * then rotate parent left, making the sibling be the_node's grandparent. |
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41 | * Now the_node has a black sibling and red parent. After rotation, |
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42 | * update sibling pointer. |
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43 | */ |
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44 | if (_RBTree_Is_red(sibling)) { |
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45 | parent->color = RBT_RED; |
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46 | sibling->color = RBT_BLACK; |
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47 | dir = the_node != parent->child[0]; |
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48 | _RBTree_Rotate(parent, dir); |
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49 | sibling = parent->child[_RBTree_Opposite_direction(dir)]; |
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50 | } |
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51 | |
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52 | /* sibling is black, see if both of its children are also black. */ |
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53 | if (!_RBTree_Is_red(sibling->child[RBT_RIGHT]) && |
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54 | !_RBTree_Is_red(sibling->child[RBT_LEFT])) { |
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55 | sibling->color = RBT_RED; |
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56 | if (_RBTree_Is_red(parent)) { |
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57 | parent->color = RBT_BLACK; |
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58 | break; |
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59 | } |
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60 | the_node = parent; /* done if parent is red */ |
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61 | parent = the_node->parent; |
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62 | sibling = _RBTree_Sibling(the_node); |
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63 | } else { |
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64 | /* at least one of sibling's children is red. we now proceed in two |
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65 | * cases, either the_node is to the left or the right of the parent. |
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66 | * In both cases, first check if one of sibling's children is black, |
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67 | * and if so rotate in the proper direction and update sibling pointer. |
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68 | * Then switch the sibling and parent colors, and rotate through parent. |
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69 | */ |
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70 | dir = the_node != parent->child[0]; |
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71 | if (!_RBTree_Is_red(sibling->child[_RBTree_Opposite_direction(dir)])) { |
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72 | sibling->color = RBT_RED; |
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73 | sibling->child[dir]->color = RBT_BLACK; |
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74 | _RBTree_Rotate(sibling, _RBTree_Opposite_direction(dir)); |
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75 | sibling = parent->child[_RBTree_Opposite_direction(dir)]; |
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76 | } |
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77 | sibling->color = parent->color; |
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78 | parent->color = RBT_BLACK; |
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79 | sibling->child[_RBTree_Opposite_direction(dir)]->color = RBT_BLACK; |
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80 | _RBTree_Rotate(parent, dir); |
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81 | break; /* done */ |
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82 | } |
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83 | } /* while */ |
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84 | if(!the_node->parent->parent) the_node->color = RBT_BLACK; |
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85 | } |
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86 | |
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87 | /** @brief Extract a Node (unprotected) |
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88 | * |
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89 | * This routine extracts (removes) @a the_node from @a the_rbtree. |
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90 | * |
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91 | * @note It does NOT disable interrupts to ensure the atomicity |
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92 | * of the extract operation. |
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93 | */ |
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94 | void _RBTree_Extract_unprotected( |
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95 | RBTree_Control *the_rbtree, |
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96 | RBTree_Node *the_node |
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97 | ) |
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98 | { |
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99 | RBTree_Node *leaf, *target; |
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100 | RBTree_Color victim_color; |
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101 | RBTree_Direction dir; |
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102 | |
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103 | if (!the_node) return; |
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104 | |
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105 | /* check if min needs to be updated */ |
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106 | if (the_node == the_rbtree->first[RBT_LEFT]) { |
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107 | RBTree_Node *next; |
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108 | next = _RBTree_Successor_unprotected(the_node); |
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109 | the_rbtree->first[RBT_LEFT] = next; |
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110 | } |
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111 | |
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112 | /* Check if max needs to be updated. min=max for 1 element trees so |
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113 | * do not use else if here. */ |
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114 | if (the_node == the_rbtree->first[RBT_RIGHT]) { |
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115 | RBTree_Node *previous; |
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116 | previous = _RBTree_Predecessor_unprotected(the_node); |
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117 | the_rbtree->first[RBT_RIGHT] = previous; |
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118 | } |
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119 | |
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120 | /* if the_node has at most one non-null child then it is safe to proceed |
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121 | * check if both children are non-null, if so then we must find a target node |
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122 | * either max in node->child[RBT_LEFT] or min in node->child[RBT_RIGHT], |
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123 | * and replace the_node with the target node. This maintains the binary |
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124 | * search tree property, but may violate the red-black properties. |
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125 | */ |
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126 | |
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127 | if (the_node->child[RBT_LEFT] && the_node->child[RBT_RIGHT]) { |
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128 | target = the_node->child[RBT_LEFT]; /* find max in node->child[RBT_LEFT] */ |
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129 | while (target->child[RBT_RIGHT]) target = target->child[RBT_RIGHT]; |
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130 | |
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131 | /* if the target node has a child, need to move it up the tree into |
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132 | * target's position (target is the right child of target->parent) |
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133 | * when target vacates it. if there is no child, then target->parent |
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134 | * should become NULL. This may cause the coloring to be violated. |
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135 | * For now we store the color of the node being deleted in victim_color. |
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136 | */ |
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137 | leaf = target->child[RBT_LEFT]; |
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138 | if(leaf) { |
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139 | leaf->parent = target->parent; |
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140 | } else { |
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141 | /* fix the tree here if the child is a null leaf. */ |
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142 | _RBTree_Extract_validate_unprotected(target); |
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143 | } |
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144 | victim_color = target->color; |
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145 | dir = target != target->parent->child[0]; |
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146 | target->parent->child[dir] = leaf; |
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147 | |
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148 | /* now replace the_node with target */ |
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149 | dir = the_node != the_node->parent->child[0]; |
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150 | the_node->parent->child[dir] = target; |
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151 | |
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152 | /* set target's new children to the original node's children */ |
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153 | target->child[RBT_RIGHT] = the_node->child[RBT_RIGHT]; |
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154 | if (the_node->child[RBT_RIGHT]) |
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155 | the_node->child[RBT_RIGHT]->parent = target; |
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156 | target->child[RBT_LEFT] = the_node->child[RBT_LEFT]; |
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157 | if (the_node->child[RBT_LEFT]) |
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158 | the_node->child[RBT_LEFT]->parent = target; |
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159 | |
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160 | /* finally, update the parent node and recolor. target has completely |
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161 | * replaced the_node, and target's child has moved up the tree if needed. |
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162 | * the_node is no longer part of the tree, although it has valid pointers |
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163 | * still. |
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164 | */ |
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165 | target->parent = the_node->parent; |
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166 | target->color = the_node->color; |
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167 | } else { |
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168 | /* the_node has at most 1 non-null child. Move the child in to |
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169 | * the_node's location in the tree. This may cause the coloring to be |
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170 | * violated. We will fix it later. |
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171 | * For now we store the color of the node being deleted in victim_color. |
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172 | */ |
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173 | leaf = the_node->child[RBT_LEFT] ? |
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174 | the_node->child[RBT_LEFT] : the_node->child[RBT_RIGHT]; |
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175 | if( leaf ) { |
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176 | leaf->parent = the_node->parent; |
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177 | } else { |
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178 | /* fix the tree here if the child is a null leaf. */ |
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179 | _RBTree_Extract_validate_unprotected(the_node); |
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180 | } |
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181 | victim_color = the_node->color; |
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182 | |
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183 | /* remove the_node from the tree */ |
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184 | dir = the_node != the_node->parent->child[0]; |
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185 | the_node->parent->child[dir] = leaf; |
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186 | } |
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187 | |
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188 | /* fix coloring. leaf has moved up the tree. The color of the deleted |
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189 | * node is in victim_color. There are two cases: |
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190 | * 1. Deleted a red node, its child must be black. Nothing must be done. |
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191 | * 2. Deleted a black node, its child must be red. Paint child black. |
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192 | */ |
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193 | if (victim_color == RBT_BLACK) { /* eliminate case 1 */ |
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194 | if (leaf) { |
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195 | leaf->color = RBT_BLACK; /* case 2 */ |
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196 | } |
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197 | } |
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198 | |
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199 | /* Wipe the_node */ |
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200 | _RBTree_Set_off_rbtree(the_node); |
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201 | |
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202 | /* set root to black, if it exists */ |
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203 | if (the_rbtree->root) the_rbtree->root->color = RBT_BLACK; |
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204 | } |
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205 | |
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206 | |
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207 | /* |
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208 | * _RBTree_Extract |
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209 | * |
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210 | * This kernel routine deletes the given node from a rbtree. |
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211 | * |
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212 | * Input parameters: |
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213 | * node - pointer to node in rbtree to be deleted |
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214 | * |
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215 | * Output parameters: NONE |
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216 | * |
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217 | * INTERRUPT LATENCY: |
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218 | * only case |
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219 | */ |
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220 | |
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221 | void _RBTree_Extract( |
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222 | RBTree_Control *the_rbtree, |
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223 | RBTree_Node *the_node |
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224 | ) |
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225 | { |
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226 | ISR_Level level; |
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227 | |
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228 | _ISR_Disable( level ); |
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229 | _RBTree_Extract_unprotected( the_rbtree, the_node ); |
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230 | _ISR_Enable( level ); |
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231 | } |
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