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<util/crc16.h>: CRC Computations(3avr) | avr-libc | <util/crc16.h>: CRC Computations(3avr) |
NAME¶
<util/crc16.h>: CRC Computations -Functions¶
static __inline__ uint16_t _crc16_update (uint16_t __crc, uint8_t __data)
Detailed Description¶
#include <util/crc16.h>This header file provides a optimized inline functions for calculating cyclic redundancy checks (CRC) using common polynomials. References:
// Dallas iButton test vector. uint8_t serno[] = { 0x02, 0x1c, 0xb8, 0x01, 0, 0, 0, 0xa2 }; int checkcrc(void) { uint8_t crc = 0, i; for (i = 0; i < sizeof serno / sizeof serno[0]; i++) crc = _crc_ibutton_update(crc, serno[i]); return crc; // must be 0 }
Function Documentation¶
static __inline__ uint16_t _crc16_update (uint16_t__crc, uint8_t__data) [static]¶
Optimized CRC-16 calculation. Polynomial: x^16 + x^15 + x^2 + 1 (0xa001)Initial value: 0xffff This CRC is normally used in disk-drive controllers. The following is the equivalent functionality written in C.
uint16_t crc16_update(uint16_t crc, uint8_t a) { int i; crc ^= a; for (i = 0; i < 8; ++i) { if (crc & 1) crc = (crc >> 1) ^ 0xA001; else crc = (crc >> 1); } return crc; }
static __inline__ uint8_t _crc8_ccitt_update (uint8_t__crc, uint8_t__data) [static]¶
Optimized CRC-8-CCITT calculation. Polynomial: x^8 + x^2 + x + 1 (0xE0)Initial value: 0x0 For use with CRC-8-ROHC
Initial value: 0xff
Reference: http://tools.ietf.org/html/rfc3095#section-5.9.1 For use with CRC-8-ATM/ITU
Initial value: 0xff
Final XOR value: 0x55
Reference: http://www.itu.int/rec/T-REC-I.432.1-199902-I/en The C equivalent has been originally written by Dave Hylands. Assembly code is based on _crc_ibutton_update optimization. The following is the equivalent functionality written in C.
uint8_t _crc8_ccitt_update (uint8_t inCrc, uint8_t inData) { uint8_t i; uint8_t data; data = inCrc ^ inData; for ( i = 0; i < 8; i++ ) { if (( data & 0x80 ) != 0 ) { data <<= 1; data ^= 0x07; } else { data <<= 1; } } return data; }
static __inline__ uint16_t _crc_ccitt_update (uint16_t__crc, uint8_t__data) [static]¶
Optimized CRC-CCITT calculation. Polynomial: x^16 + x^12 + x^5 + 1 (0x8408)Initial value: 0xffff This is the CRC used by PPP and IrDA. See RFC1171 (PPP protocol) and IrDA IrLAP 1.1 Note:
Although the CCITT polynomial is the same as that used by
the Xmodem protocol, they are quite different. The difference is in how the
bits are shifted through the alorgithm. Xmodem shifts the MSB of the CRC and
the input first, while CCITT shifts the LSB of the CRC and the input
first.
The following is the equivalent functionality written in C.
uint16_t crc_ccitt_update (uint16_t crc, uint8_t data) { data ^= lo8 (crc); data ^= data << 4; return ((((uint16_t)data << 8) | hi8 (crc)) ^ (uint8_t)(data >> 4) ^ ((uint16_t)data << 3)); }
static __inline__ uint8_t _crc_ibutton_update (uint8_t__crc, uint8_t__data) [static]¶
Optimized Dallas (now Maxim) iButton 8-bit CRC calculation. Polynomial: x^8 + x^5 + x^4 + 1 (0x8C)Initial value: 0x0 See http://www.maxim-ic.com/appnotes.cfm/appnote_number/27 The following is the equivalent functionality written in C.
uint8_t _crc_ibutton_update(uint8_t crc, uint8_t data) { uint8_t i; crc = crc ^ data; for (i = 0; i < 8; i++) { if (crc & 0x01) crc = (crc >> 1) ^ 0x8C; else crc >>= 1; } return crc; }
static __inline__ uint16_t _crc_xmodem_update (uint16_t__crc, uint8_t__data) [static]¶
Optimized CRC-XMODEM calculation. Polynomial: x^16 + x^12 + x^5 + 1 (0x1021)Initial value: 0x0 This is the CRC used by the Xmodem-CRC protocol. The following is the equivalent functionality written in C.
uint16_t crc_xmodem_update (uint16_t crc, uint8_t data) { int i; crc = crc ^ ((uint16_t)data << 8); for (i=0; i<8; i++) { if (crc & 0x8000) crc = (crc << 1) ^ 0x1021; else crc <<= 1; } return crc; }
Author¶
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