/*
 * $Id: memory.c,v 1.2 2006/02/09 03:09:04 glynn Exp $
 */

/* -*-c-basic-offset: 4;-*-
 *  Chained memory allocator 
 *  memory.c
 *
 *  Pierre de Mouveaux (pmx)  
 *  pmx@audiovu.com  - 10 april 2000.  
 *
 *  Used in GRASS 5.0 r.cost module
 *
 *  Released under GPL
 */



#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <grass/gis.h>
#include "memory.h"

#define NUM_IN_BLOCK	1024*8


struct cost* first_free = NULL;
struct cost* first = NULL;
struct cost* last = NULL;
int allocate() 
{
	struct cost* data, *p1, *p2;
	int i;

/*  	fprintf(stderr,"allocate()\n"); */

	data = (struct cost*)G_malloc(NUM_IN_BLOCK*sizeof(struct cost));

	if (data == NULL) {
		/* G_warning( */
		fprintf(stderr,"allocat(): error %s\n",strerror(errno));
		return 0;
	}

	if (last != NULL) {
		last->lower = data;
		data->higher = last;
	}

	
	p1 = p2 = data; 
	p2++;

	for (i=1; i < NUM_IN_BLOCK - 1; i++,p1++,p2++) {
		p1->lower = p2;
		p2->higher = p1;
		p1->above = NULL;
	}
	p2->higher = p1;
	p2->above = NULL;
	p2->lower = NULL;
	last = p2;
	
	if (first == NULL) {
		first_free = data;
		first = data;
	} else {
		first_free->lower = data;
	}
	
	return 1;
}

int release() {
	struct cost* p = first;
	struct cost* next;

	if (p == NULL)
		return 1;

	do {
		next = (p + NUM_IN_BLOCK) ->lower;
		G_free(p);
		p = next;
	} while (next != NULL);

	first = last = first_free = NULL;
}
			   
struct cost* get() {
	struct cost* p;

	if (first_free == NULL) {
		if (allocate() < 0) {
			/* exit(1); */
		}
	}

	p = first_free;
	first_free=p->lower;
	if (first_free->lower == NULL) {
		if (allocate() < 0) {
			/* exit(1); */
		}
	}
	return p;
}

int give(struct cost* p) {
	if (p == NULL)
		return 0;

	p->lower = first_free;
	first_free->above = p;
	first_free = p;
	p->above = NULL;	/* not used in this chain - (pmx) */
	
	return 1;
}