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https://github.com/mruby/mruby
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cubicdaiya
67de10bfcb
According to CONTRIBUTING.md, Don't use C++ style comments /* This is the prefered comment style */ Use C++ style comments only for temporary comment e.g. commenting out some code lines.
40 lines
826 B
C
40 lines
826 B
C
/*
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** crc.c - calculate CRC
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**
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** See Copyright Notice in mruby.h
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*/
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#include <limits.h>
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#include <stdint.h>
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#include <stddef.h>
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/* Calculate CRC (CRC-16-CCITT)
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**
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** 0000_0000_0000_0000_0000_0000_0000_0000
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** ^|------- CRC -------|- work --|
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** carry
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*/
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#define CRC_16_CCITT 0x11021ul /* x^16+x^12+x^5+1 */
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#define CRC_XOR_PATTERN (CRC_16_CCITT << 8)
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#define CRC_CARRY_BIT (0x01000000)
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uint16_t
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calc_crc_16_ccitt(const uint8_t *src, size_t nbytes, uint16_t crc)
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{
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size_t ibyte;
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uint32_t ibit;
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uint32_t crcwk = crc << 8;
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for (ibyte = 0; ibyte < nbytes; ibyte++) {
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crcwk |= *src++;
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for (ibit = 0; ibit < CHAR_BIT; ibit++) {
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crcwk <<= 1;
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if (crcwk & CRC_CARRY_BIT) {
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crcwk ^= CRC_XOR_PATTERN;
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}
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}
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}
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return (uint16_t)(crcwk >> 8);
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}
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