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https://github.com/torvalds/linux
23 October 2021, 00:29:24 UTC
Revision ef7d960403ecd87276e12b69c26bf0fdd5f21a0e authored by Rafael J. Wysocki on 28 August 2020, 18:58:16 UTC, committed by Rafael J. Wysocki on 28 August 2020, 18:58:16 UTC 
Merge branch 'pm-cpufreq'
 
* pm-cpufreq:
  cpufreq: Use WARN_ON_ONCE() for invalid relation
  cpufreq: No need to verify cpufreq_driver in show_scaling_cur_freq()
  Documentation: fix pm/intel_pstate build warning and wording
  cpufreq: replace cpu_logical_map() with read_cpuid_mpir()
2 parent s e3eb6e8 + 30b8e6b
Raw File
Tip revision: ef7d960403ecd87276e12b69c26bf0fdd5f21a0e authored by Rafael J. Wysocki on 28 August 2020, 18:58:16 UTC
Merge branch 'pm-cpufreq'
Tip revision: ef7d960
crc4.c 
// 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");
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