2 * Copyright 1990 William Pugh
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted.
7 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS''
8 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
9 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
10 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR
11 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
12 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
13 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
14 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
15 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
16 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
17 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
20 * Permission to include in quagga provide on March 31, 2016
24 * Skip List impementation based on code from William Pugh.
25 * ftp://ftp.cs.umd.edu/pub/skipLists/
27 * Skip Lists are a probabilistic alternative to balanced trees, as
28 * described in the June 1990 issue of CACM and were invented by
29 * William Pugh in 1987.
31 * This file contains source code to implement a dictionary using
32 * skip lists and a test driver to test the routines.
34 * A couple of comments about this implementation:
35 * The routine randomLevel has been hard-coded to generate random
36 * levels using p=0.25. It can be easily changed.
38 * The insertion routine has been implemented so as to use the
39 * dirty hack described in the CACM paper: if a random level is
40 * generated that is more than the current maximum level, the
41 * current maximum level plus one is used instead.
43 * Levels start at zero and go up to MaxLevel (which is equal to
44 * (MaxNumberOfLevels-1).
46 * The run-time flag SKIPLIST_FLAG_ALLOW_DUPLICATES determines whether or
47 * not duplicates are allowed for a given list. If set, duplicates are
48 * allowed and act in a FIFO manner. If not set, an insertion of a value
49 * already in the list updates the previously existing binding.
51 * BitsInRandom is defined to be the number of bits returned by a call to
52 * random(). For most all machines with 32-bit integers, this is 31 bits
63 #include "lib_errors.h"
66 DEFINE_MTYPE_STATIC(LIB
, SKIP_LIST
, "Skip List")
67 DEFINE_MTYPE_STATIC(LIB
, SKIP_LIST_NODE
, "Skip Node")
69 #define BitsInRandom 31
71 #define MaxNumberOfLevels 16
72 #define MaxLevel (MaxNumberOfLevels-1)
73 #define newNodeOfLevel(l) XCALLOC(MTYPE_SKIP_LIST_NODE, sizeof(struct skiplistnode)+(l)*sizeof(struct skiplistnode *))
75 static int randomsLeft
;
76 static int randomBits
;
77 static struct skiplist
*skiplist_last_created
; /* debugging hack */
80 #define CHECKLAST(sl) \
82 if ((sl)->header->forward[0] && !(sl)->last) \
84 if (!(sl)->header->forward[0] && (sl)->last) \
92 static int randomLevel(void)
94 register int level
= 0;
98 if (randomsLeft
<= 0) {
99 randomBits
= frr_weak_random();
100 randomsLeft
= BitsInRandom
/ 2;
108 if (level
>= MaxLevel
)
116 static int default_cmp(const void *key1
, const void *key2
)
125 unsigned int skiplist_count(struct skiplist
*l
)
130 struct skiplist
*skiplist_new(int flags
,
131 int (*cmp
)(const void *key1
, const void *key2
),
132 void (*del
)(void *val
))
134 struct skiplist
*new;
136 new = XCALLOC(MTYPE_SKIP_LIST
, sizeof(struct skiplist
));
141 new->header
= newNodeOfLevel(MaxNumberOfLevels
);
142 new->stats
= newNodeOfLevel(MaxNumberOfLevels
);
148 new->cmp
= default_cmp
;
153 skiplist_last_created
= new; /* debug */
158 void skiplist_free(struct skiplist
*l
)
160 register struct skiplistnode
*p
, *q
;
166 if (l
->del
&& p
!= l
->header
)
168 XFREE(MTYPE_SKIP_LIST_NODE
, p
);
172 XFREE(MTYPE_SKIP_LIST_NODE
, l
->stats
);
173 XFREE(MTYPE_SKIP_LIST
, l
);
177 int skiplist_insert(register struct skiplist
*l
, register void *key
,
178 register void *value
)
181 struct skiplistnode
*update
[MaxNumberOfLevels
];
182 register struct skiplistnode
*p
, *q
;
188 flog_err(EC_LIB_DEVELOPMENT
, "%s: key is 0, value is %p",
195 while (q
= p
->forward
[k
], q
&& (*l
->cmp
)(q
->key
, key
) < 0)
200 if (!(l
->flags
& SKIPLIST_FLAG_ALLOW_DUPLICATES
) && q
201 && ((*l
->cmp
)(q
->key
, key
) == 0)) {
210 update
[k
] = l
->header
;
213 q
= newNodeOfLevel(k
);
216 #ifdef SKIPLIST_0TIMER_DEBUG
217 q
->flags
= SKIPLIST_NODE_FLAG_INSERTED
; /* debug */
220 ++(l
->stats
->forward
[k
]);
221 #ifdef SKIPLIST_DEBUG
222 zlog_debug("%s: incremented stats @%p:%d, now %ld", __func__
, l
, k
,
223 l
->stats
->forward
[k
] - (struct skiplistnode
*)NULL
);
228 q
->forward
[k
] = p
->forward
[k
];
233 * If this is the last item in the list, update the "last" pointer
235 if (!q
->forward
[0]) {
246 int skiplist_delete(register struct skiplist
*l
, register void *key
,
247 register void *value
) /* used only if duplicates allowed */
250 struct skiplistnode
*update
[MaxNumberOfLevels
];
251 register struct skiplistnode
*p
, *q
;
255 /* to make debugging easier */
256 for (k
= 0; k
< MaxNumberOfLevels
; ++k
)
262 while (q
= p
->forward
[k
], q
&& (*l
->cmp
)(q
->key
, key
) < 0)
267 if (l
->flags
& SKIPLIST_FLAG_ALLOW_DUPLICATES
) {
268 while (q
&& ((*l
->cmp
)(q
->key
, key
) == 0)
269 && (q
->value
!= value
)) {
271 for (i
= 0; i
<= l
->level
; ++i
) {
272 if (update
[i
]->forward
[i
] == q
)
279 if (q
&& (*l
->cmp
)(q
->key
, key
) == 0) {
280 if (!(l
->flags
& SKIPLIST_FLAG_ALLOW_DUPLICATES
)
281 || (q
->value
== value
)) {
284 * found node to delete
286 #ifdef SKIPLIST_0TIMER_DEBUG
287 q
->flags
&= ~SKIPLIST_NODE_FLAG_INSERTED
;
290 * If we are deleting the last element of the list,
291 * update the list's "last" pointer.
294 if (update
[0] == l
->header
)
300 for (k
= 0; k
<= m
&& (p
= update
[k
])->forward
[k
] == q
;
302 p
->forward
[k
] = q
->forward
[k
];
304 --(l
->stats
->forward
[k
- 1]);
305 #ifdef SKIPLIST_DEBUG
306 zlog_debug("%s: decremented stats @%p:%d, now %ld",
308 l
->stats
->forward
[k
- 1]
309 - (struct skiplistnode
*)NULL
);
313 XFREE(MTYPE_SKIP_LIST_NODE
, q
);
314 while (l
->header
->forward
[m
] == NULL
&& m
> 0)
328 * Obtain first value matching "key". Unless SKIPLIST_FLAG_ALLOW_DUPLICATES
329 * is set, this will also be the only value matching "key".
331 * Also set a cursor for use with skiplist_next_value.
333 int skiplist_first_value(register struct skiplist
*l
, /* in */
334 register const void *key
, /* in */
335 void **valuePointer
, /* out */
336 void **cursor
) /* out */
339 register struct skiplistnode
*p
, *q
;
345 while (q
= p
->forward
[k
], q
&& (*l
->cmp
)(q
->key
, key
) < 0)
350 if (!q
|| (*l
->cmp
)(q
->key
, key
))
354 *valuePointer
= q
->value
;
362 int skiplist_search(register struct skiplist
*l
, register void *key
,
365 return skiplist_first_value(l
, key
, valuePointer
, NULL
);
370 * Caller supplies key and value of an existing item in the list.
371 * Function returns the value of the next list item that has the
372 * same key (useful when SKIPLIST_FLAG_ALLOW_DUPLICATES is set).
374 * Returns 0 on success. If the caller-supplied key and value
375 * do not correspond to a list element, or if they specify the
376 * last element with the given key, -1 is returned.
378 int skiplist_next_value(register struct skiplist
*l
, /* in */
379 register const void *key
, /* in */
380 void **valuePointer
, /* in/out */
381 void **cursor
) /* in/out */
384 register struct skiplistnode
*p
, *q
;
388 if (!(l
->flags
& SKIPLIST_FLAG_ALLOW_DUPLICATES
)) {
392 if (!cursor
|| !*cursor
) {
400 while (q
= p
->forward
[k
],
401 q
&& (*l
->cmp
)(q
->key
, key
) < 0)
406 * Find matching value
408 while (q
&& ((*l
->cmp
)(q
->key
, key
) == 0)
409 && (q
->value
!= *valuePointer
)) {
413 if (!q
|| ((*l
->cmp
)(q
->key
, key
) != 0)
414 || (q
->value
!= *valuePointer
)) {
422 q
= (struct skiplistnode
*)*cursor
;
431 * If we reached end-of-list or if the key is no longer the same,
434 if (!q
|| ((*l
->cmp
)(q
->key
, key
) != 0))
437 *valuePointer
= q
->value
;
444 int skiplist_first(register struct skiplist
*l
, void **keyPointer
,
447 register struct skiplistnode
*p
;
450 p
= l
->header
->forward
[0];
455 *keyPointer
= p
->key
;
458 *valuePointer
= p
->value
;
465 int skiplist_last(register struct skiplist
*l
, void **keyPointer
,
471 *keyPointer
= l
->last
->key
;
473 *valuePointer
= l
->last
->value
;
482 int skiplist_empty(register struct skiplist
*l
)
491 * Use this to walk the list. Caller sets *cursor to NULL to obtain
492 * first element. Return value of 0 indicates valid cursor/element
493 * returned, otherwise NULL cursor arg or EOL.
495 int skiplist_next(register struct skiplist
*l
, /* in */
496 void **keyPointer
, /* out */
497 void **valuePointer
, /* out */
498 void **cursor
) /* in/out */
500 struct skiplistnode
*p
;
508 p
= l
->header
->forward
[0];
519 *keyPointer
= p
->key
;
522 *valuePointer
= p
->value
;
529 int skiplist_delete_first(register struct skiplist
*l
)
532 register struct skiplistnode
*p
, *q
;
538 q
= l
->header
->forward
[0];
543 for (k
= l
->level
; k
>= 0; --k
) {
544 if (p
->forward
[k
] == q
) {
545 p
->forward
[k
] = q
->forward
[k
];
546 if ((k
== l
->level
) && (p
->forward
[k
] == NULL
)
554 #ifdef SKIPLIST_0TIMER_DEBUG
555 q
->flags
&= ~SKIPLIST_NODE_FLAG_INSERTED
;
558 * If we are deleting the last element of the list,
559 * update the list's "last" pointer.
565 --(l
->stats
->forward
[nodelevel
]);
566 #ifdef SKIPLIST_DEBUG
567 zlog_debug("%s: decremented stats @%p:%d, now %ld", __func__
, l
,
569 l
->stats
->forward
[nodelevel
] - (struct skiplistnode
*)NULL
);
575 XFREE(MTYPE_SKIP_LIST_NODE
, q
);
584 void skiplist_debug(struct vty
*vty
, struct skiplist
*l
)
589 l
= skiplist_last_created
;
590 vty_out(vty
, "Skiplist %p has max level %d\n", l
, l
->level
);
591 for (i
= l
->level
; i
>= 0; --i
)
592 vty_out(vty
, " @%d: %ld\n", i
,
593 (long)((l
->stats
->forward
[i
])
594 - (struct skiplistnode
*)NULL
));
597 static void *scramble(int i
)
601 result
= (unsigned)(i
& 0xff) << 24;
602 result
|= (unsigned)i
>> 8;
604 return (void *)result
;
607 #define sampleSize 65536
608 void skiplist_test(struct vty
*vty
)
612 void *keys
[sampleSize
];
615 zlog_debug("%s: entry", __func__
);
617 l
= skiplist_new(SKIPLIST_FLAG_ALLOW_DUPLICATES
, NULL
, NULL
);
619 zlog_debug("%s: skiplist_new returned %p", __func__
, l
);
621 for (i
= 0; i
< 4; i
++) {
623 for (k
= 0; k
< sampleSize
; k
++) {
625 zlog_debug("%s: (%d:%d)", __func__
, i
, k
);
627 // keys[k] = (void *)random();
628 keys
[k
] = scramble(k
);
629 if (skiplist_insert(l
, keys
[k
], keys
[k
]))
630 zlog_debug("error in insert #%d,#%d", i
, k
);
633 zlog_debug("%s: inserts done", __func__
);
635 for (k
= 0; k
< sampleSize
; k
++) {
638 zlog_debug("[%d:%d]", i
, k
);
639 if (skiplist_search(l
, keys
[k
], &v
))
640 zlog_debug("error in search #%d,#%d", i
, k
);
643 zlog_debug("search returned wrong value");
647 for (k
= 0; k
< sampleSize
; k
++) {
650 zlog_debug("<%d:%d>", i
, k
);
651 if (skiplist_delete(l
, keys
[k
], keys
[k
]))
652 zlog_debug("error in delete");
653 keys
[k
] = scramble(k
^ 0xf0f0f0f0);
654 if (skiplist_insert(l
, keys
[k
], keys
[k
]))
655 zlog_debug("error in insert #%d,#%d", i
, k
);
658 for (k
= 0; k
< sampleSize
; k
++) {
661 zlog_debug("{%d:%d}", i
, k
);
662 if (skiplist_delete_first(l
))
663 zlog_debug("error in delete_first");