lispsort.c

/*-------------------------------------------------------------------------
 *
 * lispsort.c--
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /cvsroot/pgsql/src/backend/lib/Attic/lispsort.c,v 1.3 1996/11/06 08:27:14 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */

#include <sys/types.h>

#include <postgres.h>

#include <nodes/pg_list.h>
#include <nodes/primnodes.h>
#include <nodes/plannodes.h>
#include <nodes/relation.h>
#include <lib/lispsort.h>
#include <lib/qsort.h>

/*
** lisp_qsort: Takes a lisp list as input, copies it into an array of lisp 
**             nodes which it sorts via qsort() with the comparison function
**             as passed into lisp_qsort(), and returns a new list with 
**             the nodes sorted.  The old list is *not* freed or modified (?)
*/
List *lisp_qsort(List *the_list,    /* the list to be sorted */
		 int (*compare)())      /* function to compare two nodes */
{
    int i;
    size_t num;
    List **nodearray;
    List *tmp, *output;
    
    /* find size of list */
    num = length(the_list);
    if (num < 2)
	return(copyObject(the_list));
    
    /* copy elements of the list into an array */
    nodearray = (List **) palloc(num * sizeof(List *));
    
    for (tmp = the_list, i = 0; tmp != NIL; tmp = lnext(tmp), i++)
	nodearray[i] = copyObject(lfirst(tmp));
    
    /* sort the array */
    pg_qsort(nodearray, num, sizeof(List *), compare);
    
    /* lcons together the array elements */
    output = NIL;
    for (i = num - 1; i >= 0; i--)
	output = lcons(nodearray[i], output);
    
    return(output);
}