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44 lines
1003 B
44 lines
1003 B
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* crc4.c - simple crc-4 calculations. |
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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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* @c: 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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