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51 lines
1.3 KiB
C++
51 lines
1.3 KiB
C++
/*****************************************************************************
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*
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* $Id$
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*
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****************************************************************************/
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#include "sii_crc.h"
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/*****************************************************************************/
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/** Calculates the SII checksum field.
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*
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* The checksum is generated with the polynom x^8+x^2+x+1 (0x07) and an
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* initial value of 0xff (see IEC 61158-6-12 ch. 5.4).
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*
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* The below code was originally generated with PYCRC
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* http://www.tty1.net/pycrc
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*
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* ./pycrc.py --width=8 --poly=0x07 --reflect-in=0 --xor-in=0xff
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* --reflect-out=0 --xor-out=0 --generate c --algorithm=bit-by-bit
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*
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* \return CRC8
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*/
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uint8_t calcSiiCrc(
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const uint8_t *data, /**< pointer to data */
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size_t length /**< number of bytes in \a data */
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)
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{
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unsigned int i;
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uint8_t bit, byte, crc = 0x48;
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while (length--) {
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byte = *data++;
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for (i = 0; i < 8; i++) {
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bit = crc & 0x80;
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crc = (crc << 1) | ((byte >> (7 - i)) & 0x01);
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if (bit) crc ^= 0x07;
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}
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}
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for (i = 0; i < 8; i++) {
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bit = crc & 0x80;
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crc <<= 1;
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if (bit) crc ^= 0x07;
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}
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return crc;
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}
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/*****************************************************************************/
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