| // SPDX-License-Identifier: GPL-2.0-only |
| * crc4.c - simple crc-4 calculations. |
| #include <linux/module.h> |
| 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. |
| * @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) |
| /* mask off anything above the top bit */ |
| 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)]; |
| MODULE_DESCRIPTION("CRC4 calculations"); |