From 181deb932074de613e33f955978af579e52e1feb Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Tue, 10 Nov 2015 18:14:30 +0100
Subject: Add efficient priority queue implementation

---
 src/pqueue.c | 134 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 134 insertions(+)
 create mode 100644 src/pqueue.c

(limited to 'src/pqueue.c')

diff --git a/src/pqueue.c b/src/pqueue.c
new file mode 100644
index 0000000..6c920b5
--- /dev/null
+++ b/src/pqueue.c
@@ -0,0 +1,134 @@
+/*
+  Copyright (c) 2012-2015, Matthias Schiffer <mschiffer@universe-factory.net>
+  All rights reserved.
+
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+
+    1. Redistributions of source code must retain the above copyright notice,
+       this list of conditions and the following disclaimer.
+    2. Redistributions in binary form must reproduce the above copyright notice,
+       this list of conditions and the following disclaimer in the documentation
+       and/or other materials provided with the distribution.
+
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+/**
+   \file
+
+   Priority queue implementation
+
+   Priority queues implemented using pairing heaps.
+*/
+
+
+#include "pqueue.h"
+#include "log.h"
+
+
+static inline void pqueue_link(fastd_pqueue_t **pqueue, fastd_pqueue_t *elem) {
+	if (elem->next)
+		exit_bug("pqueue_link: element already linked");
+
+	elem->pprev = pqueue;
+	elem->next = *pqueue;
+	if (elem->next)
+		elem->next->pprev = &elem->next;
+
+	*pqueue = elem;
+}
+
+static inline void pqueue_unlink(fastd_pqueue_t *elem) {
+	*elem->pprev = elem->next;
+	if (elem->next)
+		elem->next->pprev = elem->pprev;
+
+	elem->pprev = NULL;
+	elem->next = NULL;
+}
+
+
+static fastd_pqueue_t * pqueue_merge(fastd_pqueue_t *pqueue1, fastd_pqueue_t *pqueue2) {
+	if (!pqueue1)
+		exit_bug("pqueue_merge: pqueue1 unset");
+	if (pqueue1->next)
+		exit_bug("pqueue_merge: pqueue1 has successor");
+
+	if (!pqueue2)
+		return pqueue1;
+
+	if (pqueue2->next)
+		exit_bug("pqueue_merge: pqueue2 has successor");
+
+	fastd_pqueue_t *lo, *hi;
+
+	if (pqueue1->value < pqueue2->value) {
+		lo = pqueue1;
+		hi = pqueue2;
+	}
+	else {
+		lo = pqueue2;
+		hi = pqueue1;
+	}
+
+	pqueue_link(&lo->children, hi);
+
+	return lo;
+}
+
+static fastd_pqueue_t * pqueue_merge_pairs(fastd_pqueue_t *pqueue0) {
+	if (!pqueue0)
+		return NULL;
+
+	if (!pqueue0->pprev)
+		exit_bug("pqueue_merge_pairs: unlinked pqueue");
+
+	fastd_pqueue_t *pqueue1 = pqueue0->next;
+
+	if (!pqueue1)
+		return pqueue0;
+
+	fastd_pqueue_t *pqueue2 = pqueue1->next;
+
+	pqueue0->next = pqueue1->next = NULL;
+	pqueue0->pprev = pqueue1->pprev = NULL;
+
+	return pqueue_merge(pqueue_merge(pqueue0, pqueue1), pqueue_merge_pairs(pqueue2));
+}
+
+void fastd_pqueue_insert(fastd_pqueue_t **pqueue, fastd_pqueue_t *elem) {
+	if (elem->pprev || elem->next || elem->children)
+		exit_bug("fastd_pqueue_insert: tried to insert linked pqueue element");
+
+	*pqueue = pqueue_merge(elem, *pqueue);
+	(*pqueue)->pprev = pqueue;
+}
+
+void fastd_pqueue_remove(fastd_pqueue_t *elem) {
+	if (!fastd_pqueue_linked(elem)) {
+		if (elem->children || elem->next)
+			exit_bug("fastd_pqueue_remove: corrupted pqueue item");
+
+		return;
+	}
+
+	fastd_pqueue_t **pprev = elem->pprev;
+
+	pqueue_unlink(elem);
+
+	fastd_pqueue_t *merged = pqueue_merge_pairs(elem->children);
+	if (merged)
+		pqueue_link(pprev, merged);
+
+	elem->children = NULL;
+}
-- 
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