50 lines
1.2 KiB
C
50 lines
1.2 KiB
C
/*
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This file is part of libcapwap.
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libcapwap is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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libcapwap is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with Foobar. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "lwapp.h"
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/**
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* Calculate the 16-bit checksum for LWAPP image data message
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* elements with opcode 3 - used by Cisco also in CAPWAP
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* (But it's not always correct, the real algo might be another)
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*/
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uint16_t lw_checksum(uint8_t * d, int len)
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{
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int i;
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// uint32_t cs = 0xffff;
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if (len==0)
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return 0xffff;
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uint32_t cs = 0;
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for (i = 0; i < len; i += 2) {
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uint16_t w = d[i] << 8;
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if (i + 1 < len)
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w |= d[i + 1];
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cs += w ^= 0xffff;
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cs += cs >> 16;
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cs &= 0xffff;
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}
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return (uint16_t) cs&0xffff;
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}
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