actube/src/cw/lw_checksum.c

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/*
This file is part of libcapwap.
libcapwap is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
libcapwap 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with Foobar. If not, see <http://www.gnu.org/licenses/>.
*/
/**
*@file
*@brief Implements lw_checksum.
*@addtogroup LW
*@{
*/
#include "mbag.h"
#include "lw.h"
/**
* Calculate the 16-bit checksum for LWAPP Image Data message
* elements with opcode 3 (see RFC5412)
* This is also used by Cisco in CAPWAP
* @param d pointer to data to calulate the checksum for
* @param len length of data
* @return the calculated checksum.
*/
uint16_t lw_checksum(uint8_t * d, int len)
{
int32_t sum = 0;
uint16_t *w = (uint16_t *) d;
while (len > 1) {
sum += ntohs(*w++);
len -= 2;
}
if (len)
sum += (*(uint8_t *) w) << 8;
sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
return (~sum) & 0xffff;
}
/**
*@}
*/