1 2 /* Copyright 1998 by the Massachusetts Institute of Technology. 3 * 4 * Permission to use, copy, modify, and distribute this 5 * software and its documentation for any purpose and without 6 * fee is hereby granted, provided that the above copyright 7 * notice appear in all copies and that both that copyright 8 * notice and this permission notice appear in supporting 9 * documentation, and that the name of M.I.T. not be used in 10 * advertising or publicity pertaining to distribution of the 11 * software without specific, written prior permission. 12 * M.I.T. makes no representations about the suitability of 13 * this software for any purpose. It is provided "as is" 14 * without express or implied warranty. 15 */ 16 17 #include "ares_setup.h" 18 19 #include "ares.h" 20 #include "ares_private.h" 21 22 /* Routines for managing doubly-linked circular linked lists with a 23 * dummy head. 24 */ 25 26 /* Initialize a new head node */ 27 void ares__init_list_head(struct list_node* head) { 28 head->prev = head; 29 head->next = head; 30 head->data = NULL; 31 } 32 33 /* Initialize a list node */ 34 void ares__init_list_node(struct list_node* node, void* d) { 35 node->prev = NULL; 36 node->next = NULL; 37 node->data = d; 38 } 39 40 /* Returns true iff the given list is empty */ 41 int ares__is_list_empty(struct list_node* head) { 42 return ((head->next == head) && (head->prev == head)); 43 } 44 45 /* Inserts new_node before old_node */ 46 void ares__insert_in_list(struct list_node* new_node, 47 struct list_node* old_node) { 48 new_node->next = old_node; 49 new_node->prev = old_node->prev; 50 old_node->prev->next = new_node; 51 old_node->prev = new_node; 52 } 53 54 /* Removes the node from the list it's in, if any */ 55 void ares__remove_from_list(struct list_node* node) { 56 if (node->next != NULL) { 57 node->prev->next = node->next; 58 node->next->prev = node->prev; 59 node->prev = NULL; 60 node->next = NULL; 61 } 62 } 63 64 /* Swap the contents of two lists */ 65 void ares__swap_lists(struct list_node* head_a, 66 struct list_node* head_b) { 67 int is_a_empty = ares__is_list_empty(head_a); 68 int is_b_empty = ares__is_list_empty(head_b); 69 struct list_node old_a = *head_a; 70 struct list_node old_b = *head_b; 71 72 if (is_a_empty) { 73 ares__init_list_head(head_b); 74 } else { 75 *head_b = old_a; 76 old_a.next->prev = head_b; 77 old_a.prev->next = head_b; 78 } 79 if (is_b_empty) { 80 ares__init_list_head(head_a); 81 } else { 82 *head_a = old_b; 83 old_b.next->prev = head_a; 84 old_b.prev->next = head_a; 85 } 86 } 87
