cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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crc4.c (1003B)


      1// SPDX-License-Identifier: GPL-2.0-only
      2/*
      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 crc4
     17 * @x:    value to checksum
     18 * @bits: number of bits in @x to checksum
     19 *
     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 ignored
     23 * 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");