1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
|
/*
Generic queue utilities.
Copyright (C) 2002 Robert Lipe, robertlipe@usa.net
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111 USA
*/
#include "queue.h"
#include "stddef.h"
void
enqueue(queue *new_el, queue *old)
{
new_el->next = old->next;
new_el->prev = old;
old->next->prev = new_el;
old->next = new_el;
}
queue *
dequeue(queue *element)
{
queue *prev = element->prev;
queue *next = element->next;
next->prev = prev;
prev->next = next;
return element;
}
/*
* The following sorting code was derived from linked-list mergesort
* sample code by Simon Tatham, code obtained from:
* http://www.chiark.greenend.org.uk/~sgtatham/algorithms/listsort.html
* Modified for use with gpsbabel's queues by Paul Fox, October 2006.
*
* Original description and copyright messages follow...
*/
/*
* Demonstration code for sorting a linked list.
*
* The algorithm used is Mergesort, because that works really well
* on linked lists, without requiring the O(N) extra space it needs
* when you do it on arrays.
*
* ...
*/
/*
* This file is copyright 2001 Simon Tatham.
*
* 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 SIMON TATHAM 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.
*/
void
sortqueue (queue *qh, int (*cmp)(const queue *, const queue *))
{
queue *p, *q, *e, *tail, *oldhead, *list;
int insize, nmerges, psize, qsize, i;
/*
* Special case: if `list' is empty, we're done.
*/
if (QUEUE_EMPTY(qh))
return;
/*
* The algorithm doesn't really want the extra list head
* element. So remove the list head for now. Put it back later.
*/
list = QUEUE_FIRST(qh);
dequeue(qh);
insize = 1;
while (1) {
p = list;
oldhead = list; /* only used for circular linkage */
list = NULL;
tail = NULL;
nmerges = 0; /* count number of merges we do in this pass */
while (p) {
nmerges++; /* there exists a merge to be done */
/* step `insize' places along from p */
q = p;
psize = 0;
for (i = 0; i < insize; i++) {
psize++;
q = (q->next == oldhead ? NULL : q->next);
if (!q) break;
}
/* if q hasn't fallen off end, we have
* two lists to merge */
qsize = insize;
/* now we have two lists; merge them */
while (psize > 0 || (qsize > 0 && q)) {
/* decide whether next element of
* merge comes from p or q
*/
if (psize == 0) {
/* p is empty; e must come from q. */
e = q; q = q->next; qsize--;
if (q == oldhead) q = NULL;
} else if (qsize == 0 || !q) {
/* q is empty; e must come from p. */
e = p; p = p->next; psize--;
if (p == oldhead) p = NULL;
} else if (cmp(p,q) <= 0) {
/* First element of p is
* lower (or same); e must
* come from p.
*/
e = p; p = p->next; psize--;
if (p == oldhead) p = NULL;
} else {
/* First element of q is
* lower; e must come from
* q.
*/
e = q; q = q->next; qsize--;
if (q == oldhead) q = NULL;
}
/* add the next element to the merged list */
if (tail) {
tail->next = e;
} else {
list = e;
}
/* Maintain reverse pointers in a
* doubly linked list. */
e->prev = tail;
tail = e;
}
/* now p has stepped `insize' places
* along, and q has too */
p = q;
}
tail->next = list;
list->prev = tail;
/* If we have done only one merge, we're finished.
* Allow for nmerges==0, the empty list case.
*/
if (nmerges <= 1) {
/* Put the list head back at the start of the list */
ENQUEUE_TAIL(list, qh);
return;
}
/* Otherwise repeat, merging lists twice the size */
insize *= 2;
}
}
|
