45 lines · c
1// SPDX-License-Identifier: GPL-2.0-only2/*3 * crc4.c - simple crc-4 calculations.4 */5 6#include <linux/crc4.h>7#include <linux/module.h>8 9static const uint8_t crc4_tab[] = {10 0x0, 0x7, 0xe, 0x9, 0xb, 0xc, 0x5, 0x2,11 0x1, 0x6, 0xf, 0x8, 0xa, 0xd, 0x4, 0x3,12};13 14/**15 * crc4 - calculate the 4-bit crc of a value.16 * @c: starting crc417 * @x: value to checksum18 * @bits: number of bits in @x to checksum19 *20 * Returns the crc4 value of @x, using polynomial 0b10111.21 *22 * The @x value is treated as left-aligned, and bits above @bits are ignored23 * in the crc calculations.24 */25uint8_t crc4(uint8_t c, uint64_t x, int bits)26{27 int i;28 29 /* mask off anything above the top bit */30 x &= (1ull << bits) - 1;31 32 /* Align to 4-bits */33 bits = (bits + 3) & ~0x3;34 35 /* Calculate crc4 over four-bit nibbles, starting at the MSbit */36 for (i = bits - 4; i >= 0; i -= 4)37 c = crc4_tab[c ^ ((x >> i) & 0xf)];38 39 return c;40}41EXPORT_SYMBOL_GPL(crc4);42 43MODULE_DESCRIPTION("CRC4 calculations");44MODULE_LICENSE("GPL");45