/*
 * initialize subnet structure
 * Copyright (C) 2000  Henry Spencer.
 * 
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Library General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.  See <http://www.fsf.org/copyleft/lgpl.txt>.
 * 
 * This library 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 Library General Public
 * License for more details.
 *
 * RCSID $Id: initsubnet.c,v 1.5 2000/09/08 18:03:45 henry Exp $
 */
#include "internal.h"
#include "freeswan.h"

/*
 - initsubnet - initialize ip_subnet from address and count
 *
 * The only hard part is checking for host-part bits turned on.
 */
err_t				/* NULL for success, else string literal */
initsubnet(addr, count, clash, dst)
const ip_address *addr;
int count;
int clash;			/* '0' zero host-part bits, 'x' die on them */
ip_subnet *dst;
{
	unsigned char *p;
	int n;
	int c;
	unsigned m;
	int die;

	dst->addr = *addr;
	n = addrbytesptr(&dst->addr, (const unsigned char **)&p);
	if (n == 0)
		return "unknown address family";

	switch (clash) {
	case '0':
		die = 0;
		break;
	case 'x':
		die = 1;
		break;
	default:
		return "unknown clash-control value in initsubnet";
		break;
	}

	c = count / 8;
	if (c > n)
		return "impossible mask count";
	p += c;
	n -= c;

	m = 0xff;
	c = count % 8;
	if (n > 0 && c != 0)	/* partial byte */
		m >>= c;
	for (; n > 0; n--) {
		if ((*p & m) != 0) {
			if (die)
				return "improper subnet, host-part bits on";
			*p &= ~m;
		}
		m = 0xff;
		p++;
	}

	dst->maskbits = count;
	return NULL;
}
