18c2ecf20Sopenharmony_ci// SPDX-License-Identifier: GPL-2.0-only 28c2ecf20Sopenharmony_ci/* 38c2ecf20Sopenharmony_ci * crc4.c - simple crc-4 calculations. 48c2ecf20Sopenharmony_ci */ 58c2ecf20Sopenharmony_ci 68c2ecf20Sopenharmony_ci#include <linux/crc4.h> 78c2ecf20Sopenharmony_ci#include <linux/module.h> 88c2ecf20Sopenharmony_ci 98c2ecf20Sopenharmony_cistatic const uint8_t crc4_tab[] = { 108c2ecf20Sopenharmony_ci 0x0, 0x7, 0xe, 0x9, 0xb, 0xc, 0x5, 0x2, 118c2ecf20Sopenharmony_ci 0x1, 0x6, 0xf, 0x8, 0xa, 0xd, 0x4, 0x3, 128c2ecf20Sopenharmony_ci}; 138c2ecf20Sopenharmony_ci 148c2ecf20Sopenharmony_ci/** 158c2ecf20Sopenharmony_ci * crc4 - calculate the 4-bit crc of a value. 168c2ecf20Sopenharmony_ci * @c: starting crc4 178c2ecf20Sopenharmony_ci * @x: value to checksum 188c2ecf20Sopenharmony_ci * @bits: number of bits in @x to checksum 198c2ecf20Sopenharmony_ci * 208c2ecf20Sopenharmony_ci * Returns the crc4 value of @x, using polynomial 0b10111. 218c2ecf20Sopenharmony_ci * 228c2ecf20Sopenharmony_ci * The @x value is treated as left-aligned, and bits above @bits are ignored 238c2ecf20Sopenharmony_ci * in the crc calculations. 248c2ecf20Sopenharmony_ci */ 258c2ecf20Sopenharmony_ciuint8_t crc4(uint8_t c, uint64_t x, int bits) 268c2ecf20Sopenharmony_ci{ 278c2ecf20Sopenharmony_ci int i; 288c2ecf20Sopenharmony_ci 298c2ecf20Sopenharmony_ci /* mask off anything above the top bit */ 308c2ecf20Sopenharmony_ci x &= (1ull << bits) - 1; 318c2ecf20Sopenharmony_ci 328c2ecf20Sopenharmony_ci /* Align to 4-bits */ 338c2ecf20Sopenharmony_ci bits = (bits + 3) & ~0x3; 348c2ecf20Sopenharmony_ci 358c2ecf20Sopenharmony_ci /* Calculate crc4 over four-bit nibbles, starting at the MSbit */ 368c2ecf20Sopenharmony_ci for (i = bits - 4; i >= 0; i -= 4) 378c2ecf20Sopenharmony_ci c = crc4_tab[c ^ ((x >> i) & 0xf)]; 388c2ecf20Sopenharmony_ci 398c2ecf20Sopenharmony_ci return c; 408c2ecf20Sopenharmony_ci} 418c2ecf20Sopenharmony_ciEXPORT_SYMBOL_GPL(crc4); 428c2ecf20Sopenharmony_ci 438c2ecf20Sopenharmony_ciMODULE_DESCRIPTION("CRC4 calculations"); 448c2ecf20Sopenharmony_ciMODULE_LICENSE("GPL"); 45