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+/* Copyright (c) 2010 the authors listed at the following URL, and/or
+the authors of referenced articles or incorporated external code:
+http://en.literateprograms.org/Skip_list_(C)?action=history&offset=20080313195128
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+Retrieved from: http://en.literateprograms.org/Skip_list_(C)?oldid=12811
+*/
+
+/*
+ * Modifications by Lubos Slovak, 2010-2011
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#include <string.h>
+#include <assert.h>
+
+//#include "common.h"
+#include "common/skip-list.h"
+
+#define ERR_ALLOC_FAILED fprintf(stderr, "Allocation failed at %s:%d\n", \
+ __FILE__, __LINE__)
+
+/*----------------------------------------------------------------------------*/
+
+static const float P = 0.5;
+
+/*!
+ * \brief Maximum level of a node, i.e. maximum number of skip list levels.
+ */
+static const int MAX_LEVEL = 6;
+
+/*----------------------------------------------------------------------------*/
+/* Private functions */
+/*----------------------------------------------------------------------------*/
+/*!
+ * \brief Generates random real number between 0 and 1.
+ */
+static float frand()
+{
+ unsigned seed = (unsigned)time(0);
+ return (float) rand_r(&seed) / RAND_MAX;
+}
+
+/*----------------------------------------------------------------------------*/
+/*!
+ * \brief Returns random level between 0 and MAX_LEVEL.
+ */
+static int skip_random_level()
+{
+ static int first = 1;
+ int lvl = 0;
+
+ if (first) {
+ first = 0;
+ }
+
+ while (frand() < P && lvl < MAX_LEVEL) {
+ lvl++;
+ }
+
+ return lvl;
+}
+
+/*----------------------------------------------------------------------------*/
+/*!
+ * \brief Creates a new skip list node with the given key and value.
+ *
+ * \param level Level of the skip list node.
+ * \param key Key of the new node.
+ * \param value Value to be stored in the node.
+ *
+ * \return Pointer to the newly created node or NULL if not successful.
+ */
+static skip_node_t *skip_make_node(int level, void *key, void *value)
+{
+ skip_node_t *sn = (skip_node_t *)malloc(sizeof(skip_node_t));
+ if (sn == NULL) {
+ ERR_ALLOC_FAILED;
+ return NULL;
+ }
+
+ sn->forward = (skip_node_t **)calloc(level + 1, sizeof(skip_node_t *));
+ if (sn->forward == NULL) {
+ ERR_ALLOC_FAILED;
+ free(sn);
+ return NULL;
+ }
+ sn->key = key;
+ sn->value = value;
+ return sn;
+}
+
+/*----------------------------------------------------------------------------*/
+/*!
+ * \brief Properly deallocates the given skip list node, and optionally destroys
+ * its key and value.
+ *
+ * \param node Skip list node to be deleted.
+ * \param destroy_key Function for properly destroying the key. If set tu NULL,
+ * the object at which the key points will not be destroyed.
+ * \param destroy_value Function for properly destroying the key. If set tu
+ * NULL, the object at which the value points will not be
+ * destroyed.
+ */
+static void skip_delete_node(skip_node_t **node, void (*destroy_key)(void *),
+ void (*destroy_value)(void *))
+{
+ if (destroy_key != NULL) {
+ destroy_key((*node)->key);
+ }
+ if (destroy_value != NULL) {
+ destroy_value((*node)->value);
+ }
+
+ free((*node)->forward);
+ free(*node);
+
+ node = NULL;
+}
+
+/*----------------------------------------------------------------------------*/
+/* Public functions */
+/*----------------------------------------------------------------------------*/
+
+skip_list_t *skip_create_list(int (*compare_keys)(void *, void *))
+{
+ assert(compare_keys != NULL);
+
+ skip_list_t *ss = (skip_list_t *)malloc(sizeof(skip_list_t));
+ if (ss == NULL) {
+ ERR_ALLOC_FAILED;
+ return NULL;
+ }
+
+ ss->head = skip_make_node(MAX_LEVEL, NULL, NULL);
+ if (ss->head == NULL) {
+ ERR_ALLOC_FAILED;
+ free(ss);
+ return NULL;
+ }
+
+ ss->level = 0;
+ ss->compare_keys = compare_keys;
+
+ return ss;
+}
+
+/*----------------------------------------------------------------------------*/
+
+void skip_destroy_list(skip_list_t **list, void (*destroy_key)(void *),
+ void (*destroy_value)(void *))
+{
+ assert((*list) != NULL);
+ assert((*list)->head != NULL);
+
+ skip_node_t *x;
+
+ while ((*list)->head->forward[0] != NULL) {
+ x = (*list)->head->forward[0];
+ for (int i = 0; i <= (*list)->level; i++) {
+ if ((*list)->head->forward[i] != x) {
+ break;
+ }
+ (*list)->head->forward[i] = x->forward[i];
+ }
+
+ // delete the item
+ skip_delete_node(&x, destroy_key, destroy_value);
+
+ while ((*list)->level > 0
+ && (*list)->head->forward[(*list)->level] == NULL) {
+ (*list)->level--;
+ }
+ }
+
+ // free the head
+ skip_delete_node(&(*list)->head, NULL, NULL);
+
+ free(*list);
+ *list = NULL;
+}
+
+/*----------------------------------------------------------------------------*/
+
+void *skip_find(const skip_list_t *list, void *key)
+{
+ assert(list != NULL);
+ assert(list->head != NULL);
+ assert(list->compare_keys != NULL);
+
+ int i;
+ skip_node_t *x = list->head;
+ for (i = list->level; i >= 0; i--) {
+ while (x->forward[i] != NULL
+ && list->compare_keys(x->forward[i]->key, key) == -1) {
+ x = x->forward[i];
+ }
+ }
+ x = x->forward[0];
+
+ if (x != NULL && list->compare_keys(x->key, key) == 0) {
+ return x->value;
+ }
+ return NULL;
+}
+
+/*----------------------------------------------------------------------------*/
+
+void *skip_find_less_or_equal(const skip_list_t *list, void *key)
+{
+ assert(list != NULL);
+ assert(list->head != NULL);
+ assert(list->compare_keys != NULL);
+
+ int i;
+ skip_node_t *x = list->head;
+ for (i = list->level; i >= 0; i--) {
+ while (x->forward[i] != NULL
+ && list->compare_keys(x->forward[i]->key, key) <= 0) {
+ x = x->forward[i];
+ }
+ }
+
+ return x->value;
+}
+
+/*----------------------------------------------------------------------------*/
+
+int skip_insert(skip_list_t *list, void *key, void *value,
+ int (*merge_values)(void **, void **))
+{
+ assert(list != NULL);
+ assert(list->head != NULL);
+ assert(list->compare_keys != NULL);
+
+ int i;
+ skip_node_t *x = list->head;
+ skip_node_t *update[MAX_LEVEL + 1];
+ memset(update, 0, MAX_LEVEL + 1);
+
+ for (i = list->level; i >= 0; i--) {
+ while (x->forward[i] != NULL
+ && list->compare_keys(x->forward[i]->key, key) == -1) {
+ x = x->forward[i];
+ }
+ update[i] = x;
+ }
+ x = x->forward[0];
+
+ if (x == NULL || list->compare_keys(x->key, key) != 0) {
+ int lvl = skip_random_level();
+
+ if (lvl > list->level) {
+ for (i = list->level + 1; i <= lvl; i++) {
+ update[i] = list->head;
+ }
+ list->level = lvl;
+ }
+
+ x = skip_make_node(lvl, key, value);
+ if (x == NULL) {
+ ERR_ALLOC_FAILED;
+ return -1;
+ }
+
+ for (i = 0; i <= lvl; i++) {
+ x->forward[i] = update[i]->forward[i];
+ update[i]->forward[i] = x;
+ }
+
+ return 0;
+ } else { // already in the list
+ if (merge_values != NULL) { // if merge function provided, merge
+ return (merge_values(&x->value, &value) == 0) ? 2 : -2;
+ } else {
+ return 1;
+ }
+ }
+}
+
+/*----------------------------------------------------------------------------*/
+
+int skip_remove(skip_list_t *list, void *key, void (*destroy_key)(void *),
+ void (*destroy_value)(void *))
+{
+ assert(list != NULL);
+ assert(list->head != NULL);
+ assert(list->compare_keys != NULL);
+
+ int i;
+ skip_node_t *x = list->head;
+ skip_node_t *update[MAX_LEVEL + 1];
+ memset(update, 0, MAX_LEVEL + 1);
+
+ for (i = list->level; i >= 0; i--) {
+ while (x->forward[i] != NULL
+ && list->compare_keys(x->forward[i]->key, key) == -1) {
+ x = x->forward[i];
+ }
+ update[i] = x;
+ }
+ x = x->forward[0];
+
+ if (x != NULL && list->compare_keys(x->key, key) == 0) {
+ for (i = 0; i <= list->level; i++) {
+ if (update[i]->forward[i] != x) {
+ break;
+ }
+ update[i]->forward[i] = x->forward[i];
+ }
+
+ // delete the item
+ skip_delete_node(&x, destroy_key, destroy_value);
+
+ while (list->level > 0
+ && list->head->forward[list->level] == NULL) {
+ list->level--;
+ }
+ return 0;
+ } else {
+ return -1;
+ }
+}
+
+/*----------------------------------------------------------------------------*/
+
+int skip_is_empty(const skip_list_t *list)
+{
+ if (!list) {
+ return 1;
+ }
+
+ return (list->head->forward[0] == NULL);
+}
+
+/*----------------------------------------------------------------------------*/
+
+const skip_node_t *skip_first(const skip_list_t *list)
+{
+ if (!list) {
+ return NULL;
+ }
+
+ return list->head->forward[0];
+}
+
+/*----------------------------------------------------------------------------*/
+
+const skip_node_t *skip_next(const skip_node_t *node)
+{
+ return node->forward[0];
+}
+
+/*----------------------------------------------------------------------------*/
+
+void skip_print_list(const skip_list_t *list,
+ void (*print_item)(void *, void *))
+{
+ assert(list != NULL);
+ assert(list->head != NULL);
+ assert(list->compare_keys != NULL);
+ assert(print_item != NULL);
+
+ skip_node_t *x = list->head->forward[0];
+ while (x != NULL) {
+ print_item(x->key, x->value);
+ x = x->forward[0];
+ }
+}
+
+/*----------------------------------------------------------------------------*/
+
+skip_list_t *skip_copy_list(const skip_list_t *list)
+{
+ skip_list_t *ss = (skip_list_t *)malloc(sizeof(skip_list_t));
+ if (ss == NULL) {
+ ERR_ALLOC_FAILED;
+ return NULL;
+ }
+
+ ss->head = skip_make_node(list->level, NULL, NULL);
+ if (ss->head == NULL) {
+ ERR_ALLOC_FAILED;
+ free(ss);
+ return NULL;
+ }
+
+ ss->level = list->level;
+ ss->compare_keys = list->compare_keys;
+
+ skip_node_t *x = list->head->forward[0];
+ skip_node_t *prev = list->head;
+ skip_node_t *new_prev = ss->head;
+ while (x != NULL) {
+ //print_item(x->key, x->value);
+
+ // create new node
+ skip_node_t *n = skip_make_node(list->level, x->key, x->value);
+ if (n == NULL) {
+ skip_destroy_list(&ss, NULL, NULL);
+ return NULL;
+ }
+ // set forward pointers from the previous node
+ for (int i = 0; i <= list->level; ++i) {
+ if (prev->forward[i] == x) {
+ new_prev->forward[i] = n;
+ }
+ }
+
+ prev = x;
+ x = x->forward[0];
+ new_prev = n;
+ }
+
+ return ss;
+}
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