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/*
* Library: libcrc
* Git: https://github.com/lammertb/libcrc
* Author: Lammert Bies
*
* This file is licensed under the MIT License as stated below
*
* Copyright (c) 1999-2016 Lammert Bies
* Copyright (c) 2020 Thomas A. Early, N7TAE
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*
* Description
* -----------
* The source file contains routines which calculate the CCITT CRC
* values for an incomming byte string.
*/
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include "crc.h"
#define CRC_POLY_16 0x5935u
#define CRC_START_16 0xFFFFu
CCRC::CCRC()
{
for (uint16_t i=0; i<256; i++)
{
uint16_t crc = 0;
uint16_t c = i << 8;
for (uint16_t j=0; j<8; j++)
{
if ( (crc ^ c) & 0x8000 )
crc = ( crc << 1 ) ^ CRC_POLY_16;
else
crc = crc << 1;
c = c << 1;
}
crc_tab16[i] = crc;
}
}
uint16_t CCRC::CalcCRC( const uint8_t *input_str, size_t num_bytes ) const
{
uint16_t crc = CRC_START_16;
if ( input_str )
for (size_t a=0; a<num_bytes; a++)
{
crc = (crc << 8) ^ crc_tab16[ ((crc >> 8) ^ uint16_t(input_str[a])) & 0x00FF ];
}
return crc;
}