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Add skip list implementation (many thanks to Keith Packard)
The files here are copied directly from the standalone skiplist module available from: git clone git://cworth.org/~cworth/skiplist In particular the files come from the double branch and the following commit on that branch: 8b5a439c68e220cf1514d9b3141a1dbdce8af585 Also of interest is the original skiplist module hosted by Keith Packard that is the original implementation on which these files were based. Since the cworth/skiplist branched off of keithp's, Keith has also now implemented a doubly-linked variant which might be interesting for further simplification of the code. See: git clone git://keithp.com/git/skiplist and the double-link branch there.
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Carl Worth
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87
src/cairo-skiplist-private.h
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87
src/cairo-skiplist-private.h
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/*
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* Copyright © 2006 Keith Packard
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* Copyright © 2006 Carl Worth
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*
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* Permission to use, copy, modify, distribute, and sell this software and its
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* documentation for any purpose is hereby granted without fee, provided that
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* the above copyright notice appear in all copies and that both that copyright
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* notice and this permission notice appear in supporting documentation, and
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* that the name of the copyright holders not be used in advertising or
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* publicity pertaining to distribution of the software without specific,
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* written prior permission. The copyright holders make no representations
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* about the suitability of this software for any purpose. It is provided "as
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* is" without express or implied warranty.
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*
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* THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
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* INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
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* EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
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* CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
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* DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
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* TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
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* OF THIS SOFTWARE.
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*/
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#ifndef SKIPLIST_H
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#define SKIPLIST_H
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#define MAX_LEVEL 31
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/*
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* Skip list element. In order to use the skip list, the caller must
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* generate a structure for list elements that has as its final member
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* a skip_elt_t, (which will be allocated with variable size).
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*
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* The caller must also pass the size of the structure to
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* skip_list_init.
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*/
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typedef struct _skip_elt {
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int prev_index;
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struct _skip_elt *prev;
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struct _skip_elt *next[1];
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} skip_elt_t;
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#define SKIP_LIST_ELT_TO_DATA(type, elt) ((type *) ((char *) (elt) - (sizeof (type) - sizeof (skip_elt_t))))
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typedef int
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(*skip_list_compare_t) (void *list, void *a, void *b);
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typedef struct _skip_list {
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skip_list_compare_t compare;
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size_t elt_size;
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size_t data_size;
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skip_elt_t *chains[MAX_LEVEL];
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int max_level;
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} skip_list_t;
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/* Initialize a new skip list. The compare function accepts a pointer
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* to the list as well as pointers to two elements. The function must
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* return a value greater than zero, zero, or less then 0 if the first
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* element is considered respectively greater than, equal to, or less
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* than the second element. The size of each object, (as computed by
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* sizeof) is passed for elt_size. Note that the structure used for
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* list elements must have as its final member a skip_elt_t
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*/
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void
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skip_list_init (skip_list_t *list,
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skip_list_compare_t compare,
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size_t elt_size);
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/* Insert a new element into the list at the correct sort order as
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* determined by compare. Data will be copied (elt_size bytes from
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* <data> via memcpy). The new element is returned. */
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void *
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skip_list_insert (skip_list_t *list, void *data);
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/* Find an element which compare considers equal to <data> */
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void *
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skip_list_find (skip_list_t *list, void *data);
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/* Delete an element which compare considers equal to <data> */
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void
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skip_list_delete (skip_list_t *list, void *data);
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/* Delete the given element from the list. */
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void
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skip_list_delete_given (skip_list_t *list, skip_elt_t *given);
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#endif
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238
src/cairo-skiplist.c
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238
src/cairo-skiplist.c
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/*
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* Copyright © 2006 Keith Packard
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* Copyright © 2006 Carl Worth
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*
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* Permission to use, copy, modify, distribute, and sell this software and its
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* documentation for any purpose is hereby granted without fee, provided that
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* the above copyright notice appear in all copies and that both that copyright
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* notice and this permission notice appear in supporting documentation, and
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* that the name of the copyright holders not be used in advertising or
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* publicity pertaining to distribution of the software without specific,
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* written prior permission. The copyright holders make no representations
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* about the suitability of this software for any purpose. It is provided "as
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* is" without express or implied warranty.
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*
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* THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
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* INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
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* EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
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* CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
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* DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
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* TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
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* OF THIS SOFTWARE.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <stddef.h>
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#include <string.h>
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#include <assert.h>
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#include "cairo-skiplist-private.h"
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#define ELT_DATA(elt) (void *) ((char*) (elt) - list->data_size)
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#define NEXT_TO_ELT(next) (skip_elt_t *) ((char *) (next) - offsetof (skip_elt_t, next))
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/*
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* Initialize an empty skip list
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*/
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void
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skip_list_init (skip_list_t *list,
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skip_list_compare_t compare,
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size_t elt_size)
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{
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int i;
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list->compare = compare;
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list->elt_size = elt_size;
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list->data_size = elt_size - sizeof (skip_elt_t);
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for (i = 0; i < MAX_LEVEL; i++)
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list->chains[i] = NULL;
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list->max_level = 0;
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}
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/*
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* Generate a random level number, distributed
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* so that each level is 1/4 as likely as the one before
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*
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* Note that level numbers run 1 <= level <= MAX_LEVEL
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*/
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static int
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random_level (void)
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{
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/* tricky bit -- each bit is '1' 75% of the time */
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long int bits = random () | random ();
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int level = 0;
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while (++level < MAX_LEVEL)
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{
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if (bits & 1)
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break;
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bits >>= 1;
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}
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return level;
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}
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/*
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* Insert 'data' into the list
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*/
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void *
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skip_list_insert (skip_list_t *list, void *data)
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{
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skip_elt_t **update[MAX_LEVEL];
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char *data_and_elt;
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skip_elt_t *elt, *prev, **next;
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int i, level, prev_index;
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level = random_level ();
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prev_index = level - 1;
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/*
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* Find links along each chain
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*/
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prev = NULL;
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next = list->chains;
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for (i = list->max_level; --i >= 0; )
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{
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for (; (elt = next[i]); next = elt->next)
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{
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if (list->compare (list, ELT_DATA(elt), data) > 0)
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break;
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}
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update[i] = next;
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if (i == prev_index && next != list->chains)
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prev = NEXT_TO_ELT (next);
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}
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/*
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* Create new list element
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*/
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if (level > list->max_level)
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{
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level = list->max_level + 1;
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prev_index = level - 1;
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update[list->max_level] = list->chains;
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list->max_level = level;
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}
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data_and_elt = malloc (list->elt_size + (level-1) * sizeof (skip_elt_t *));
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memcpy (data_and_elt, data, list->data_size);
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elt = (skip_elt_t *) (data_and_elt + list->data_size);
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elt->prev_index = prev_index;
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elt->prev = prev;
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/*
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* Insert into all chains
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*/
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for (i = 0; i < level; i++)
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{
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elt->next[i] = update[i][i];
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if (elt->next[i] && elt->next[i]->prev_index == i)
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elt->next[i]->prev = elt;
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update[i][i] = elt;
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}
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return data_and_elt;
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}
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void *
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skip_list_find (skip_list_t *list, void *data)
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{
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int i;
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skip_elt_t **next = list->chains;
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skip_elt_t *elt;
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/*
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* Walk chain pointers one level at a time
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*/
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for (i = list->max_level; --i >= 0;)
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while (next[i] && list->compare (list, data, ELT_DATA(next[i])) > 0)
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{
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next = next[i]->next;
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}
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/*
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* Here we are
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*/
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elt = next[0];
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if (elt && list->compare (list, data, ELT_DATA (elt)) == 0)
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return ELT_DATA (elt);
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return NULL;
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}
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void
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skip_list_delete (skip_list_t *list, void *data)
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{
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skip_elt_t **update[MAX_LEVEL], *prev[MAX_LEVEL];
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skip_elt_t *elt, **next;
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int i;
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/*
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* Find links along each chain
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*/
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next = list->chains;
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for (i = list->max_level; --i >= 0; )
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{
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for (; (elt = next[i]); next = elt->next)
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{
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if (list->compare (list, ELT_DATA (elt), data) >= 0)
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break;
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}
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update[i] = &next[i];
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if (next == list->chains)
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prev[i] = NULL;
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else
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prev[i] = NEXT_TO_ELT (next);
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}
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elt = next[0];
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assert (list->compare (list, ELT_DATA (elt), data) == 0);
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for (i = 0; i < list->max_level && *update[i] == elt; i++) {
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*update[i] = elt->next[i];
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if (elt->next[i] && elt->next[i]->prev_index == i)
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elt->next[i]->prev = prev[i];
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}
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while (list->max_level > 0 && list->chains[list->max_level - 1] == NULL)
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list->max_level--;
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free (ELT_DATA (elt));
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}
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void
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skip_list_delete_given (skip_list_t *list, skip_elt_t *given)
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{
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skip_elt_t **update[MAX_LEVEL], *prev[MAX_LEVEL];
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skip_elt_t *elt, **next;
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int i;
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/*
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* Find links along each chain
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*/
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if (given->prev)
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next = given->prev->next;
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else
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next = list->chains;
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for (i = given->prev_index + 1; --i >= 0; )
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{
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for (; (elt = next[i]); next = elt->next)
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{
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if (elt == given)
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break;
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}
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update[i] = &next[i];
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if (next == list->chains)
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prev[i] = NULL;
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else
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prev[i] = NEXT_TO_ELT (next);
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}
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elt = next[0];
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assert (elt == given);
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for (i = 0; i < (given->prev_index + 1) && *update[i] == elt; i++) {
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*update[i] = elt->next[i];
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if (elt->next[i] && elt->next[i]->prev_index == i)
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elt->next[i]->prev = prev[i];
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}
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while (list->max_level > 0 && list->chains[list->max_level - 1] == NULL)
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list->max_level--;
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free (ELT_DATA (elt));
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}
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