47 lines
1.1 KiB
C
47 lines
1.1 KiB
C
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/*
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* crc4.c - simple crc-4 calculations.
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*
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* This source code is licensed under the GNU General Public License, Version
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* 2. See the file COPYING for more details.
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*/
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#include <linux/crc4.h>
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#include <linux/module.h>
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static const uint8_t crc4_tab[] = {
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0x0, 0x7, 0xe, 0x9, 0xb, 0xc, 0x5, 0x2,
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0x1, 0x6, 0xf, 0x8, 0xa, 0xd, 0x4, 0x3,
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};
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/**
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* crc4 - calculate the 4-bit crc of a value.
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* @crc: starting crc4
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* @x: value to checksum
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* @bits: number of bits in @x to checksum
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*
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* Returns the crc4 value of @x, using polynomial 0b10111.
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*
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* The @x value is treated as left-aligned, and bits above @bits are ignored
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* in the crc calculations.
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*/
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uint8_t crc4(uint8_t c, uint64_t x, int bits)
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{
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int i;
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/* mask off anything above the top bit */
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x &= (1ull << bits) - 1;
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/* Align to 4-bits */
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bits = (bits + 3) & ~0x3;
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/* Calculate crc4 over four-bit nibbles, starting at the MSbit */
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for (i = bits - 4; i >= 0; i -= 4)
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c = crc4_tab[c ^ ((x >> i) & 0xf)];
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return c;
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}
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EXPORT_SYMBOL_GPL(crc4);
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MODULE_DESCRIPTION("CRC4 calculations");
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MODULE_LICENSE("GPL");
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