Framework for reading and writing variables in real time on any MBED platform.
DistantIO
This is the C implementation of the DistantIO slave framework.
Library is working but slight API breaks may occur in the future. C++ version is also in development.
To get the master-side implementation, see https://github.com/Overdrivr/DistantIO
crc.cpp@0:c4676d32d381, 2015-09-15 (annotated)
- Committer:
- Overdrivr
- Date:
- Tue Sep 15 15:27:55 2015 +0000
- Revision:
- 0:c4676d32d381
- Child:
- 1:aaffeb93f99b
Version not bug free (especially names should not be longer thant 8 characters or have spaces), but pretty reliable behavior. See github repo for tickets
Who changed what in which revision?
User | Revision | Line number | New contents of line |
---|---|---|---|
Overdrivr | 0:c4676d32d381 | 1 | // From : http://stackoverflow.com/questions/15169387/definitive-crc-for-c |
Overdrivr | 0:c4676d32d381 | 2 | /* 8-bit CRC with polynomial x^8+x^6+x^3+x^2+1, 0x14D. |
Overdrivr | 0:c4676d32d381 | 3 | Chosen based on Koopman, et al. (0xA6 in his notation = 0x14D >> 1): |
Overdrivr | 0:c4676d32d381 | 4 | http://www.ece.cmu.edu/~koopman/roses/dsn04/koopman04_crc_poly_embedded.pdf |
Overdrivr | 0:c4676d32d381 | 5 | */ |
Overdrivr | 0:c4676d32d381 | 6 | |
Overdrivr | 0:c4676d32d381 | 7 | #include "crc.h" |
Overdrivr | 0:c4676d32d381 | 8 | /* |
Overdrivr | 0:c4676d32d381 | 9 | static const unsigned char crc8_table[] = { |
Overdrivr | 0:c4676d32d381 | 10 | 0x00, 0x3e, 0x7c, 0x42, 0xf8, 0xc6, 0x84, 0xba, 0x95, 0xab, 0xe9, 0xd7, |
Overdrivr | 0:c4676d32d381 | 11 | 0x6d, 0x53, 0x11, 0x2f, 0x4f, 0x71, 0x33, 0x0d, 0xb7, 0x89, 0xcb, 0xf5, |
Overdrivr | 0:c4676d32d381 | 12 | 0xda, 0xe4, 0xa6, 0x98, 0x22, 0x1c, 0x5e, 0x60, 0x9e, 0xa0, 0xe2, 0xdc, |
Overdrivr | 0:c4676d32d381 | 13 | 0x66, 0x58, 0x1a, 0x24, 0x0b, 0x35, 0x77, 0x49, 0xf3, 0xcd, 0x8f, 0xb1, |
Overdrivr | 0:c4676d32d381 | 14 | 0xd1, 0xef, 0xad, 0x93, 0x29, 0x17, 0x55, 0x6b, 0x44, 0x7a, 0x38, 0x06, |
Overdrivr | 0:c4676d32d381 | 15 | 0xbc, 0x82, 0xc0, 0xfe, 0x59, 0x67, 0x25, 0x1b, 0xa1, 0x9f, 0xdd, 0xe3, |
Overdrivr | 0:c4676d32d381 | 16 | 0xcc, 0xf2, 0xb0, 0x8e, 0x34, 0x0a, 0x48, 0x76, 0x16, 0x28, 0x6a, 0x54, |
Overdrivr | 0:c4676d32d381 | 17 | 0xee, 0xd0, 0x92, 0xac, 0x83, 0xbd, 0xff, 0xc1, 0x7b, 0x45, 0x07, 0x39, |
Overdrivr | 0:c4676d32d381 | 18 | 0xc7, 0xf9, 0xbb, 0x85, 0x3f, 0x01, 0x43, 0x7d, 0x52, 0x6c, 0x2e, 0x10, |
Overdrivr | 0:c4676d32d381 | 19 | 0xaa, 0x94, 0xd6, 0xe8, 0x88, 0xb6, 0xf4, 0xca, 0x70, 0x4e, 0x0c, 0x32, |
Overdrivr | 0:c4676d32d381 | 20 | 0x1d, 0x23, 0x61, 0x5f, 0xe5, 0xdb, 0x99, 0xa7, 0xb2, 0x8c, 0xce, 0xf0, |
Overdrivr | 0:c4676d32d381 | 21 | 0x4a, 0x74, 0x36, 0x08, 0x27, 0x19, 0x5b, 0x65, 0xdf, 0xe1, 0xa3, 0x9d, |
Overdrivr | 0:c4676d32d381 | 22 | 0xfd, 0xc3, 0x81, 0xbf, 0x05, 0x3b, 0x79, 0x47, 0x68, 0x56, 0x14, 0x2a, |
Overdrivr | 0:c4676d32d381 | 23 | 0x90, 0xae, 0xec, 0xd2, 0x2c, 0x12, 0x50, 0x6e, 0xd4, 0xea, 0xa8, 0x96, |
Overdrivr | 0:c4676d32d381 | 24 | 0xb9, 0x87, 0xc5, 0xfb, 0x41, 0x7f, 0x3d, 0x03, 0x63, 0x5d, 0x1f, 0x21, |
Overdrivr | 0:c4676d32d381 | 25 | 0x9b, 0xa5, 0xe7, 0xd9, 0xf6, 0xc8, 0x8a, 0xb4, 0x0e, 0x30, 0x72, 0x4c, |
Overdrivr | 0:c4676d32d381 | 26 | 0xeb, 0xd5, 0x97, 0xa9, 0x13, 0x2d, 0x6f, 0x51, 0x7e, 0x40, 0x02, 0x3c, |
Overdrivr | 0:c4676d32d381 | 27 | 0x86, 0xb8, 0xfa, 0xc4, 0xa4, 0x9a, 0xd8, 0xe6, 0x5c, 0x62, 0x20, 0x1e, |
Overdrivr | 0:c4676d32d381 | 28 | 0x31, 0x0f, 0x4d, 0x73, 0xc9, 0xf7, 0xb5, 0x8b, 0x75, 0x4b, 0x09, 0x37, |
Overdrivr | 0:c4676d32d381 | 29 | 0x8d, 0xb3, 0xf1, 0xcf, 0xe0, 0xde, 0x9c, 0xa2, 0x18, 0x26, 0x64, 0x5a, |
Overdrivr | 0:c4676d32d381 | 30 | 0x3a, 0x04, 0x46, 0x78, 0xc2, 0xfc, 0xbe, 0x80, 0xaf, 0x91, 0xd3, 0xed, |
Overdrivr | 0:c4676d32d381 | 31 | 0x57, 0x69, 0x2b, 0x15}; |
Overdrivr | 0:c4676d32d381 | 32 | |
Overdrivr | 0:c4676d32d381 | 33 | unsigned crc8(unsigned char *data, uint16_t len) |
Overdrivr | 0:c4676d32d381 | 34 | { |
Overdrivr | 0:c4676d32d381 | 35 | static unsigned char crc; |
Overdrivr | 0:c4676d32d381 | 36 | unsigned char *end; |
Overdrivr | 0:c4676d32d381 | 37 | |
Overdrivr | 0:c4676d32d381 | 38 | if (len == 0) |
Overdrivr | 0:c4676d32d381 | 39 | return crc; |
Overdrivr | 0:c4676d32d381 | 40 | |
Overdrivr | 0:c4676d32d381 | 41 | crc ^= 0xff; |
Overdrivr | 0:c4676d32d381 | 42 | end = data + len; |
Overdrivr | 0:c4676d32d381 | 43 | do { |
Overdrivr | 0:c4676d32d381 | 44 | crc = crc8_table[crc ^ *data++]; |
Overdrivr | 0:c4676d32d381 | 45 | } while (data < end); |
Overdrivr | 0:c4676d32d381 | 46 | return crc ^ 0xff; |
Overdrivr | 0:c4676d32d381 | 47 | return 0; |
Overdrivr | 0:c4676d32d381 | 48 | }*/ |
Overdrivr | 0:c4676d32d381 | 49 | |
Overdrivr | 0:c4676d32d381 | 50 | /* this was used to generate the table and to test the table-version |
Overdrivr | 0:c4676d32d381 | 51 | |
Overdrivr | 0:c4676d32d381 | 52 | #define POLY 0xB2 |
Overdrivr | 0:c4676d32d381 | 53 | |
Overdrivr | 0:c4676d32d381 | 54 | unsigned crc8_slow(unsigned crc, unsigned char *data, size_t len) |
Overdrivr | 0:c4676d32d381 | 55 | { |
Overdrivr | 0:c4676d32d381 | 56 | unsigned char *end; |
Overdrivr | 0:c4676d32d381 | 57 | |
Overdrivr | 0:c4676d32d381 | 58 | if (len == 0) |
Overdrivr | 0:c4676d32d381 | 59 | return crc; |
Overdrivr | 0:c4676d32d381 | 60 | crc ^= 0xff; |
Overdrivr | 0:c4676d32d381 | 61 | end = data + len; |
Overdrivr | 0:c4676d32d381 | 62 | do { |
Overdrivr | 0:c4676d32d381 | 63 | crc ^= *data++; |
Overdrivr | 0:c4676d32d381 | 64 | crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1; |
Overdrivr | 0:c4676d32d381 | 65 | crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1; |
Overdrivr | 0:c4676d32d381 | 66 | crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1; |
Overdrivr | 0:c4676d32d381 | 67 | crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1; |
Overdrivr | 0:c4676d32d381 | 68 | crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1; |
Overdrivr | 0:c4676d32d381 | 69 | crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1; |
Overdrivr | 0:c4676d32d381 | 70 | crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1; |
Overdrivr | 0:c4676d32d381 | 71 | crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1; |
Overdrivr | 0:c4676d32d381 | 72 | } while (data < end); |
Overdrivr | 0:c4676d32d381 | 73 | return crc ^ 0xff; |
Overdrivr | 0:c4676d32d381 | 74 | } |
Overdrivr | 0:c4676d32d381 | 75 | */ |
Overdrivr | 0:c4676d32d381 | 76 | /* |
Overdrivr | 0:c4676d32d381 | 77 | # From : https://en.wikipedia.org/wiki/Computation_of_cyclic_redundancy_checks |
Overdrivr | 0:c4676d32d381 | 78 | |
Overdrivr | 0:c4676d32d381 | 79 | # Most significant bit first (big-endian) |
Overdrivr | 0:c4676d32d381 | 80 | # x^16+x^12+x^5+1 = (1) 0001 0000 0010 0001 = 0x1021 |
Overdrivr | 0:c4676d32d381 | 81 | |
Overdrivr | 0:c4676d32d381 | 82 | def crc16(data): |
Overdrivr | 0:c4676d32d381 | 83 | rem = 0 |
Overdrivr | 0:c4676d32d381 | 84 | n = 16 |
Overdrivr | 0:c4676d32d381 | 85 | # A popular variant complements rem here |
Overdrivr | 0:c4676d32d381 | 86 | for d in data: |
Overdrivr | 0:c4676d32d381 | 87 | rem = rem ^ (d << (n-8)) # n = 16 in this example |
Overdrivr | 0:c4676d32d381 | 88 | for j in range(1,8): |
Overdrivr | 0:c4676d32d381 | 89 | # Assuming 8 bits per byte |
Overdrivr | 0:c4676d32d381 | 90 | if rem & 0x8000: |
Overdrivr | 0:c4676d32d381 | 91 | # if leftmost (most significant) bit is set |
Overdrivr | 0:c4676d32d381 | 92 | rem = (rem << 1) ^ 0x1021 |
Overdrivr | 0:c4676d32d381 | 93 | else: |
Overdrivr | 0:c4676d32d381 | 94 | rem = rem << 1 |
Overdrivr | 0:c4676d32d381 | 95 | rem = rem & 0xffff # Trim remainder to 16 bits |
Overdrivr | 0:c4676d32d381 | 96 | # A popular variant complements rem here |
Overdrivr | 0:c4676d32d381 | 97 | return rem |
Overdrivr | 0:c4676d32d381 | 98 | */ |
Overdrivr | 0:c4676d32d381 | 99 | // Most significant bit first (big-endian) |
Overdrivr | 0:c4676d32d381 | 100 | // x^16+x^12+x^5+1 = (1) 0001 0000 0010 0001 = 0x1021 |
Overdrivr | 0:c4676d32d381 | 101 | |
Overdrivr | 0:c4676d32d381 | 102 | uint16_t crc16(uint8_t* data, uint16_t len) |
Overdrivr | 0:c4676d32d381 | 103 | { |
Overdrivr | 0:c4676d32d381 | 104 | uint16_t rem = 0; |
Overdrivr | 0:c4676d32d381 | 105 | uint16_t n = 16; |
Overdrivr | 0:c4676d32d381 | 106 | // A popular variant complements rem here |
Overdrivr | 0:c4676d32d381 | 107 | for(uint16_t i = 0 ; i < len ; i++) |
Overdrivr | 0:c4676d32d381 | 108 | { |
Overdrivr | 0:c4676d32d381 | 109 | rem = rem ^ (data[i] << (n-8)); // n = 16 in this example |
Overdrivr | 0:c4676d32d381 | 110 | |
Overdrivr | 0:c4676d32d381 | 111 | for(uint16_t j = 1 ; j < 8 ; j++) // Assuming 8 bits per byte |
Overdrivr | 0:c4676d32d381 | 112 | { |
Overdrivr | 0:c4676d32d381 | 113 | |
Overdrivr | 0:c4676d32d381 | 114 | if(rem & 0x8000) |
Overdrivr | 0:c4676d32d381 | 115 | { |
Overdrivr | 0:c4676d32d381 | 116 | // if leftmost (most significant) bit is set |
Overdrivr | 0:c4676d32d381 | 117 | rem = (rem << 1) ^ 0x1021; |
Overdrivr | 0:c4676d32d381 | 118 | } |
Overdrivr | 0:c4676d32d381 | 119 | else |
Overdrivr | 0:c4676d32d381 | 120 | { |
Overdrivr | 0:c4676d32d381 | 121 | rem = rem << 1; |
Overdrivr | 0:c4676d32d381 | 122 | } |
Overdrivr | 0:c4676d32d381 | 123 | rem &= 0xffff; // Trim remainder to 16 bits |
Overdrivr | 0:c4676d32d381 | 124 | } |
Overdrivr | 0:c4676d32d381 | 125 | } |
Overdrivr | 0:c4676d32d381 | 126 | // A popular variant complements rem here |
Overdrivr | 0:c4676d32d381 | 127 | return rem; |
Overdrivr | 0:c4676d32d381 | 128 | } |
Overdrivr | 0:c4676d32d381 | 129 | |
Overdrivr | 0:c4676d32d381 | 130 |