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56 lines
1.0 KiB
C
56 lines
1.0 KiB
C
/*
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* Copyright (C) 2013 Freie Universität Berlin.
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*
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* This file is subject to the terms and conditions of the GNU Lesser
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* General Public License v2.1. See the file LICENSE in the top level
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* directory for more details.
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*/
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/**
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* @{
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* @file net_help.c
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* @brief Providing implementation for prototypes defined in net_help.h.
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* @author Oliver Gesch <oliver.gesch@googlemail.com>
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*/
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#include <stdio.h>
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#include <string.h>
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#include "thread.h"
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#include "net_help.h"
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uint16_t net_help_csum(uint16_t sum, uint8_t *buf, uint16_t len)
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{
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int count = len >> 1;
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if (count) {
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uint16_t carry = 0;
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do {
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uint16_t t = (*buf << 8) + *(buf + 1);
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count--;
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buf += 2;
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sum += carry;
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sum += t;
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carry = (t > sum);
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} while (count);
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sum += carry;
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}
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if (len & 1) {
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uint16_t u = (*buf << 8);
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sum += (*buf << 8);
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if (sum < u) {
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sum++;
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}
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}
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return sum;
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}
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/**
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* @}
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*/
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