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 ```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 ``` ``````/* * crc4.c - simple crc-4 calculations. * * This source code is licensed under the GNU General Public License, Version * 2. See the file COPYING for more details. */ #include #include static const uint8_t crc4_tab[] = { 0x0, 0x7, 0xe, 0x9, 0xb, 0xc, 0x5, 0x2, 0x1, 0x6, 0xf, 0x8, 0xa, 0xd, 0x4, 0x3, }; /** * crc4 - calculate the 4-bit crc of a value. * @c: starting crc4 * @x: value to checksum * @bits: number of bits in @x to checksum * * Returns the crc4 value of @x, using polynomial 0b10111. * * The @x value is treated as left-aligned, and bits above @bits are ignored * in the crc calculations. */ uint8_t crc4(uint8_t c, uint64_t x, int bits) { int i; /* mask off anything above the top bit */ x &= (1ull << bits) - 1; /* Align to 4-bits */ bits = (bits + 3) & ~0x3; /* Calculate crc4 over four-bit nibbles, starting at the MSbit */ for (i = bits - 4; i >= 0; i -= 4) c = crc4_tab[c ^ ((x >> i) & 0xf)]; return c; } EXPORT_SYMBOL_GPL(crc4); MODULE_DESCRIPTION("CRC4 calculations"); MODULE_LICENSE("GPL"); ``````