/* Copyright (c) 2002, 2003, 2004 Marek Michalkiewicz All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. * Neither the name of the copyright holders nor the names of contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ /* $Id: crc16.h,v 1.1 2005/11/05 22:23:16 joerg_wunsch Exp $ */ #ifndef _UTIL_CRC16_H_ #define _UTIL_CRC16_H_ #include /** \defgroup util_crc : CRC Computations \code#include \endcode This header file provides a optimized inline functions for calculating 16 bit cyclic redundancy checks (CRC) using common polynomials. \par References: \par See the Dallas Semiconductor app note 27 for 8051 assembler example and general CRC optimization suggestions. The table on the last page of the app note is the key to understanding these implementations. \par Jack Crenshaw's "Implementing CRCs" article in the January 1992 isue of \e Embedded \e Systems \e Programming. This may be difficult to find, but it explains CRC's in very clear and concise terms. Well worth the effort to obtain a copy. */ /** \ingroup util_crc Optimized CRC-16 calcutation. Polynomial: x^16 + x^15 + x^2 + 1 (0xa001)
Initial value: 0xffff This CRC is normally used in disk-drive controllers. */ static __inline__ uint16_t _crc16_update(uint16_t __crc, uint8_t __data) { uint8_t __tmp; uint16_t __ret; __asm__ __volatile__ ( "eor %A0,%2" "\n\t" "mov %1,%A0" "\n\t" "swap %1" "\n\t" "eor %1,%A0" "\n\t" "mov __tmp_reg__,%1" "\n\t" "lsr %1" "\n\t" "lsr %1" "\n\t" "eor %1,__tmp_reg__" "\n\t" "mov __tmp_reg__,%1" "\n\t" "lsr %1" "\n\t" "eor %1,__tmp_reg__" "\n\t" "andi %1,0x07" "\n\t" "mov __tmp_reg__,%A0" "\n\t" "mov %A0,%B0" "\n\t" "lsr %1" "\n\t" "ror __tmp_reg__" "\n\t" "ror %1" "\n\t" "mov %B0,__tmp_reg__" "\n\t" "eor %A0,%1" "\n\t" "lsr __tmp_reg__" "\n\t" "ror %1" "\n\t" "eor %B0,__tmp_reg__" "\n\t" "eor %A0,%1" : "=r" (__ret), "=d" (__tmp) : "r" (__data), "0" (__crc) : "r0" ); return __ret; } /** \ingroup util_crc 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. \code 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; } \endcode */ static __inline__ uint16_t _crc_xmodem_update(uint16_t __crc, uint8_t __data) { uint16_t __ret; /* %B0:%A0 (alias for __crc) */ uint8_t __tmp1; /* %1 */ uint8_t __tmp2; /* %2 */ /* %3 __data */ __asm__ __volatile__ ( "eor %B0,%3" "\n\t" /* crc.hi ^ data */ "mov __tmp_reg__,%B0" "\n\t" "swap __tmp_reg__" "\n\t" /* swap(crc.hi ^ data) */ /* Calculate the ret.lo of the CRC. */ "mov %1,__tmp_reg__" "\n\t" "andi %1,0x0f" "\n\t" "eor %1,%B0" "\n\t" "mov %2,%B0" "\n\t" "eor %2,__tmp_reg__" "\n\t" "lsl %2" "\n\t" "andi %2,0xe0" "\n\t" "eor %1,%2" "\n\t" /* __tmp1 is now ret.lo. */ /* Calculate the ret.hi of the CRC. */ "mov %2,__tmp_reg__" "\n\t" "eor %2,%B0" "\n\t" "andi %2,0xf0" "\n\t" "lsr %2" "\n\t" "mov __tmp_reg__,%B0" "\n\t" "lsl __tmp_reg__" "\n\t" "rol %2" "\n\t" "lsr %B0" "\n\t" "lsr %B0" "\n\t" "lsr %B0" "\n\t" "andi %B0,0x1f" "\n\t" "eor %B0,%2" "\n\t" "eor %B0,%A0" "\n\t" /* ret.hi is now ready. */ "mov %A0,%1" "\n\t" /* ret.lo is now ready. */ : "=d" (__ret), "=d" (__tmp1), "=d" (__tmp2) : "r" (__data), "0" (__crc) : "r0" ); return __ret; } /** \ingroup util_crc 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. \code 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)); } \endcode */ static __inline__ uint16_t _crc_ccitt_update (uint16_t __crc, uint8_t __data) { uint16_t __ret; __asm__ __volatile__ ( "eor %A0,%1" "\n\t" "mov __tmp_reg__,%A0" "\n\t" "swap %A0" "\n\t" "andi %A0,0xf0" "\n\t" "eor %A0,__tmp_reg__" "\n\t" "mov __tmp_reg__,%B0" "\n\t" "mov %B0,%A0" "\n\t" "swap %A0" "\n\t" "andi %A0,0x0f" "\n\t" "eor __tmp_reg__,%A0" "\n\t" "lsr %A0" "\n\t" "eor %B0,%A0" "\n\t" "eor %A0,%B0" "\n\t" "lsl %A0" "\n\t" "lsl %A0" "\n\t" "lsl %A0" "\n\t" "eor %A0,__tmp_reg__" : "=d" (__ret) : "r" (__data), "0" (__crc) : "r0" ); return __ret; } #endif /* _UTIL_CRC16_H_ */