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crc.c
Go to the documentation of this file.
1 /*
2 *
3 * Copyright (c) 2014, Freescale Semiconductor, Inc.
4 *
5 */
6
7 /*!
8 * @file crc.h
9 * @brief CRC source file that implements the CCITT CRC16 standard.
10 *
11 */
12
13 #include "isf.h"
14 #include "crc.h"
15
16
17
18 uint16 ccitt_crc16_cal(uint32 anumBytes, uint8 *apBuf)
19 {
20
21 uint16 crc16 = 0xffff;
22 uint8 *p8 = (uint8*)apBuf;
23 uint8 bit;
24 uint16 xor_flag;
25
26 while(anumBytes--)
27 {
28
29 uint8 v;
30
31 // Align test bit with leftmost bit of the message byte.
32 v = 0x80;
33
34
35 bit = 0;
36 do
37 {
38 if (crc16 & 0x8000)
39 {
40 xor_flag= 1;
41 }
42 else
43 {
44 xor_flag= 0;
45 }
46 crc16 = crc16 << 1;
47
48
49 if (*p8 & v)
50 {
51 // If not zero, then append the next bit of the message to the
52 // end of the CRC. The zero bit placed there by the shift above
53 // need not be changed if the next bit of the message is zero.
54 crc16 = crc16 + 1;
55 }
56
57 if (xor_flag)
58 {
59 crc16 = crc16 ^ POLY_CRC16_GENERATOR;
60 }
61
62 // Align test bit with next bit of the message byte.
63 v = v >> 1;
64
65 } while(++bit < 8);
66
67 p8++;
68 }
69
70
71 bit = 0;
72 do
73 {
74 if (crc16 & 0x8000)
75 {
76 xor_flag= 1;
77 }
78 else
79 {
80 xor_flag= 0;
81 }
82 crc16 = crc16 << 1;
83
84 if (xor_flag)
85 {
86 crc16 = crc16 ^ POLY_CRC16_GENERATOR;
87 }
88 } while(++bit < 16);
89
90
91
92 return crc16;
93 }
94
uint8
unsigned char uint8
This defines uint8 as unsigned char.
Definition: isf_types.h:18
crc.h
CRC header file.
uint32
unsigned long uint32
This defines uint32 as unsigned long.
Definition: isf_types.h:36
POLY_CRC16_GENERATOR
#define POLY_CRC16_GENERATOR
The standard polynomial value used for CCITT CRC 16-bit calculation.
Definition: crc.h:19
ccitt_crc16_cal
uint16 ccitt_crc16_cal(uint32 anumBytes, uint8 *apBuf)
This crc function contains the standard CCITT CRC 16-bit implementation.
Definition: crc.c:18
isf.h
Main ISF header file. Contains code common to all ISF components.
uint16
unsigned short uint16
This defines uint16 as unsigned short.
Definition: isf_types.h:27
- © Freescale Semiconductor, Inc. 2015. All Rights Reserved.