RIOT/sys/net/crosslayer/net_help/net_help.c

/*
 * Copyright (C) 2013  Freie Universität Berlin.
 *
 * This file is subject to the terms and conditions of the GNU Lesser
 * General Public License v2.1. See the file LICENSE in the top level
 * directory for more details.
 */

/**
 * @{
 * @file    net_help.c
 * @brief   Providing implementation for prototypes defined in net_help.h.
 * @author  Oliver Gesch <oliver.gesch@googlemail.com>
 */

#include <stdio.h>
#include <string.h>
#include "thread.h"

#include "net_help.h"

uint16_t net_help_csum(uint16_t sum, uint8_t *buf, uint16_t len)
{
    int count = len >> 1;

    if (count) {
        uint16_t carry = 0;

        do {
            uint16_t t = (*buf << 8) + *(buf + 1);
            count--;
            buf += 2;
            sum += carry;
            sum += t;
            carry = (t > sum);
        } while (count);

        sum += carry;
    }

    if (len & 1) {
        uint16_t u = (*buf << 8);
        sum += (*buf << 8);

        if (sum < u) {
            sum++;
        }
    }

    return sum;
}

/**
 * @}
 */