104 lines
3.8 KiB
C
104 lines
3.8 KiB
C
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/*
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* Library: libcrc
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* File: src/crc8.c
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* Author: Lammert Bies
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*
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* This file is licensed under the MIT License as stated below
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*
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* Copyright (c) 1999-2016 Lammert Bies
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*
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* Description
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* -----------
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* The source file src/crc8.c contains routines for the calculation of 8 bit
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* CRC values according to the calculation rules used in the SHT1x and SHT7x
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* series of temperature and humidity sensors.
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*/
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#include <stdlib.h>
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#include "checksum.h"
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/*
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* static uint8_t sht75_crc_table[];
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*
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* The SHT75 humidity sensor is capable of calculating an 8 bit CRC checksum to
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* ensure data integrity. The lookup table crc_table[] is used to recalculate
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* the CRC.
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*/
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static uint8_t sht75_crc_table[] = {
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0, 49, 98, 83, 196, 245, 166, 151, 185, 136, 219, 234, 125, 76, 31, 46,
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67, 114, 33, 16, 135, 182, 229, 212, 250, 203, 152, 169, 62, 15, 92, 109,
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134, 183, 228, 213, 66, 115, 32, 17, 63, 14, 93, 108, 251, 202, 153, 168,
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197, 244, 167, 150, 1, 48, 99, 82, 124, 77, 30, 47, 184, 137, 218, 235,
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61, 12, 95, 110, 249, 200, 155, 170, 132, 181, 230, 215, 64, 113, 34, 19,
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126, 79, 28, 45, 186, 139, 216, 233, 199, 246, 165, 148, 3, 50, 97, 80,
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187, 138, 217, 232, 127, 78, 29, 44, 2, 51, 96, 81, 198, 247, 164, 149,
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248, 201, 154, 171, 60, 13, 94, 111, 65, 112, 35, 18, 133, 180, 231, 214,
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122, 75, 24, 41, 190, 143, 220, 237, 195, 242, 161, 144, 7, 54, 101, 84,
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57, 8, 91, 106, 253, 204, 159, 174, 128, 177, 226, 211, 68, 117, 38, 23,
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252, 205, 158, 175, 56, 9, 90, 107, 69, 116, 39, 22, 129, 176, 227, 210,
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191, 142, 221, 236, 123, 74, 25, 40, 6, 55, 100, 85, 194, 243, 160, 145,
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71, 118, 37, 20, 131, 178, 225, 208, 254, 207, 156, 173, 58, 11, 88, 105,
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4, 53, 102, 87, 192, 241, 162, 147, 189, 140, 223, 238, 121, 72, 27, 42,
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193, 240, 163, 146, 5, 52, 103, 86, 120, 73, 26, 43, 188, 141, 222, 239,
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130, 179, 224, 209, 70, 119, 36, 21, 59, 10, 89, 104, 255, 206, 157, 172
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};
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/*
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* uint8_t crc_8( const unsigned char *input_str, size_t num_bytes );
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*
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* The function crc_8() calculates the 8 bit wide CRC of an input string of a
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* given length.
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*/
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uint8_t crc_8( const unsigned char *input_str, size_t num_bytes ) {
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size_t a;
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uint8_t crc;
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const unsigned char *ptr;
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crc = CRC_START_8;
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ptr = input_str;
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if ( ptr != NULL ) for (a=0; a<num_bytes; a++) {
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crc = sht75_crc_table[(*ptr++) ^ crc];
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}
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return crc;
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} /* crc_8 */
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/*
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* uint8_t update_crc_8( unsigned char crc, unsigned char val );
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*
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* Given a databyte and the previous value of the CRC value, the function
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* update_crc_8() calculates and returns the new actual CRC value of the data
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* comming in.
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*/
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uint8_t update_crc_8( unsigned char crc, unsigned char val ) {
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return sht75_crc_table[val ^ crc];
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} /* update_crc_8 */
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