// SPDX-License-Identifier: GPL-2.0-only /* * crc4.c - simple crc-4 calculations. */ #include <linux/crc4.h> #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. * @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");