/*
 * This file is part of the UCB release of Plan 9. It is subject to the license
 * terms in the LICENSE file found in the top-level directory of this
 * distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
 * part of the UCB release of Plan 9, including this file, may be copied,
 * modified, propagated, or distributed except according to the terms contained
 * in the LICENSE file.
 */
#include <stdlib.h>

#include <iplib/iplib.h>
#include <parlib/parlib.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>

static short endian = 1;
static uint8_t *aendian = (uint8_t *)&endian;
#define LITTLE *aendian

/* "Returns the one's complement checksum used in IP protocols."  That's from
 * Plan 9's man page.  This is not a usable, as is - you want to call
 * ip_calc_xsum(). */
uint16_t ptclbsum(uint8_t *addr, int len)
{
	uint32_t losum, hisum, mdsum, x;
	uint32_t t1, t2;

	losum = 0;
	hisum = 0;
	mdsum = 0;

	x = 0;
	if ((uintptr_t)addr & 1) {
		if (len) {
			hisum += addr[0];
			len--;
			addr++;
		}
		x = 1;
	}
	while(len >= 16) {
		t1 = *(uint16_t*)(addr + 0);
		t2 = *(uint16_t*)(addr + 2);	mdsum += t1;
		t1 = *(uint16_t*)(addr + 4);	mdsum += t2;
		t2 = *(uint16_t*)(addr + 6);	mdsum += t1;
		t1 = *(uint16_t*)(addr + 8);	mdsum += t2;
		t2 = *(uint16_t*)(addr + 10);	mdsum += t1;
		t1 = *(uint16_t*)(addr + 12);	mdsum += t2;
		t2 = *(uint16_t*)(addr + 14);	mdsum += t1;
		mdsum += t2;
		len -= 16;
		addr += 16;
	}
	while (len >= 2) {
		mdsum += *(uint16_t *)addr;
		len -= 2;
		addr += 2;
	}
	if (x) {
		if (len)
			losum += addr[0];
		if (LITTLE)
			losum += mdsum;
		else
			hisum += mdsum;
	} else {
		if (len)
			hisum += addr[0];
		if (LITTLE)
			hisum += mdsum;
		else
			losum += mdsum;
	}

	losum += hisum >> 8;
	losum += (hisum & 0xff) << 8;
	while (hisum = losum >> 16)
		losum = hisum + (losum & 0xffff);

	return losum & 0xffff;
}

/* Calculates an IP checksum for [addr, addr + len), returning the xsum in host
 * endian. */
uint16_t ip_calc_xsum(uint8_t *addr, size_t len)
{
	return ~ptclbsum(addr, len) & 0xffff;
}