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comparison crc8.c @ 9:7da9a3f23592

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Import ds18x20 code
author Matt Johnston <matt@ucc.asn.au>
date Fri, 18 May 2012 23:57:08 +0800
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8:c55321727d02 9:7da9a3f23592
1 /* please read copyright-notice at EOF */
2
3 #include <stdint.h>
4
5 #define CRC8INIT 0x00
6 #define CRC8POLY 0x18 //0X18 = X^8+X^5+X^4+X^0
7
8 uint8_t crc8( uint8_t *data, uint16_t number_of_bytes_in_data )
9 {
10 uint8_t crc;
11 uint16_t loop_count;
12 uint8_t bit_counter;
13 uint8_t b;
14 uint8_t feedback_bit;
15
16 crc = CRC8INIT;
17
18 for (loop_count = 0; loop_count != number_of_bytes_in_data; loop_count++)
19 {
20 b = data[loop_count];
21
22 bit_counter = 8;
23 do {
24 feedback_bit = (crc ^ b) & 0x01;
25
26 if ( feedback_bit == 0x01 ) {
27 crc = crc ^ CRC8POLY;
28 }
29 crc = (crc >> 1) & 0x7F;
30 if ( feedback_bit == 0x01 ) {
31 crc = crc | 0x80;
32 }
33
34 b = b >> 1;
35 bit_counter--;
36
37 } while (bit_counter > 0);
38 }
39
40 return crc;
41 }
42
43 /*
44 This code is from Colin O'Flynn - Copyright (c) 2002
45 only minor changes by M.Thomas 9/2004
46
47 Permission is hereby granted, free of charge, to any person obtaining a copy of
48 this software and associated documentation files (the "Software"), to deal in
49 the Software without restriction, including without limitation the rights to
50 use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
51 the Software, and to permit persons to whom the Software is furnished to do so,
52 subject to the following conditions:
53
54 The above copyright notice and this permission notice shall be included in all
55 copies or substantial portions of the Software.
56
57 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
58 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
59 FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
60 COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
61 IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
62 CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
63 */