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/* $Id: listsort.c,v 1.4 2005/02/21 05:29:33 danmc Exp $ */
/*----------------------------------------------------------------*
* Linked list sorting code taken from
* http://www.chiark.greenend.org.uk/~sgtatham/algorithms/listsort.html
* and hacked to serve in gattrib by SDB.
*----------------------------------------------------------------*/
/*
* 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 code can handle singly and doubly linked lists, and
* circular and linear lists too. For any serious application,
* you'll probably want to remove the conditionals on `is_circular'
* and `is_double' to adapt the code to your own purpose.
*
*/
/*
* 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.
*/
/* --- We don't need these 'cause they are already defined elsewhere ---
* #define FALSE 0
* #define TRUE 1
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <stdio.h>
#ifdef HAVE_STRING_H
#include <string.h>
#endif
/*------------------------------------------------------------------
* Gattrib specific includes
*------------------------------------------------------------------*/
#include <libgeda/libgeda.h> /* geda library fcns */
#include "../include/struct.h" /* typdef and struct declarations */
#include "../include/prototype.h" /* function prototypes */
#include "../include/globals.h"
#ifdef HAVE_LIBDMALLOC
#include <dmalloc.h>
#endif
/*----------------------------------------------------------------*
* Comparison function -- compare values of string data.
*----------------------------------------------------------------*/
int cmp(STRING_LIST *a, STRING_LIST *b) {
return strcmp(a->data, b->data);
}
/*----------------------------------------------------------------*
* This is the actual sort function. Notice that it returns the new
* head of the list. (It has to, because the head will not
* generally be the same element after the sort.) So unlike sorting
* an array, where you can do
*
* sort(myarray);
*
* you now have to do
*
* list = listsort(mylist);
*----------------------------------------------------------------*/
STRING_LIST *listsort(STRING_LIST *list, int is_circular, int is_double) {
STRING_LIST *p, *q, *e, *tail, *oldhead;
int insize, nmerges, psize, qsize, i;
/*
* Silly special case: if `list' was passed in as NULL, return
* NULL immediately.
*/
if (!list)
return NULL;
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++;
if (is_circular)
q = (q->next == oldhead ? NULL : q->next);
else
q = 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 (is_circular && q == oldhead) q = NULL;
} else if (qsize == 0 || !q) {
/* q is empty; e must come from p. */
e = p; p = p->next; psize--;
if (is_circular && 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 (is_circular && p == oldhead) p = NULL;
} else {
/* First element of q is lower; e must come from q. */
e = q; q = q->next; qsize--;
if (is_circular && q == oldhead) q = NULL;
}
/* add the next element to the merged list */
if (tail) {
tail->next = e;
} else {
list = e;
}
if (is_double) {
/* 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;
}
if (is_circular) {
tail->next = list;
if (is_double)
list->prev = tail;
} else
tail->next = NULL;
/* If we have done only one merge, we're finished. */
if (nmerges <= 1) /* allow for nmerges==0, the empty list case */
return list;
/* Otherwise repeat, merging lists twice the size */
insize *= 2;
}
}
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