| 1 | |
| 2 | |
| 3 | * crc4.c - simple crc-4 calculations.
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| 4 |
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| 5 |
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| 6 | #include <linux/crc4.h>
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| 7 | #include <linux/module.h>
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| 8 |
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| 9 | static const uint8_t crc4_tab[] = {
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| 10 | 0x0, 0x7, 0xe, 0x9, 0xb, 0xc, 0x5, 0x2,
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| 11 | 0x1, 0x6, 0xf, 0x8, 0xa, 0xd, 0x4, 0x3,
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| 12 | };
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| 13 |
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| 14 | |
| 15 | * crc4 - calculate the 4-bit crc of a value.
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| 16 | * @c: starting crc4
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| 17 | * @x: value to checksum
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| 18 | * @bits: number of bits in @x to checksum
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| 19 | *
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| 20 | * Returns the crc4 value of @x, using polynomial 0b10111.
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| 21 | *
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| 22 | * The @x value is treated as left-aligned, and bits above @bits are ignored
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| 23 | * in the crc calculations.
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| 24 |
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| 25 | uint8_t crc4(uint8_t c, uint64_t x, int bits)
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| 26 | {
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| 27 | int i;
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| 28 |
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| 29 |
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| 30 | x &= (1ull << bits) - 1;
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| 31 |
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| 32 |
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| 33 | bits = (bits + 3) & ~0x3;
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| 34 |
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| 35 |
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| 36 | for (i = bits - 4; i >= 0; i -= 4)
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| 37 | c = crc4_tab[c ^ ((x >> i) & 0xf)];
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| 38 |
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| 39 | return c;
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| 40 | }
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| 41 | EXPORT_SYMBOL_GPL(crc4);
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| 42 |
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| 43 | MODULE_DESCRIPTION("CRC4 calculations");
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| 44 | MODULE_LICENSE("GPL");
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