mdadm/crc32c.c

/*
 * Oct 28, 2015 Song Liu simplified the code and port it to mdadm
 *
 * Aug 8, 2011 Bob Pearson with help from Joakim Tjernlund and George Spelvin
 * cleaned up code to current version of sparse and added the slicing-by-8
 * algorithm to the closely similar existing slicing-by-4 algorithm.
 *
 * Oct 15, 2000 Matt Domsch <Matt_Domsch@dell.com>
 * Nicer crc32 functions/docs submitted by linux@horizon.com.  Thanks!
 * Code was from the public domain, copyright abandoned.  Code was
 * subsequently included in the kernel, thus was re-licensed under the
 * GNU GPL v2.
 *
 * Oct 12, 2000 Matt Domsch <Matt_Domsch@dell.com>
 * Same crc32 function was used in 5 other places in the kernel.
 * I made one version, and deleted the others.
 * There are various incantations of crc32().  Some use a seed of 0 or ~0.
 * Some xor at the end with ~0.  The generic crc32() function takes
 * seed as an argument, and doesn't xor at the end.  Then individual
 * users can do whatever they need.
 *   drivers/net/smc9194.c uses seed ~0, doesn't xor with ~0.
 *   fs/jffs2 uses seed 0, doesn't xor with ~0.
 *   fs/partitions/efi.c uses seed ~0, xor's with ~0.
 *
 * This source code is licensed under the GNU General Public License,
 * Version 2.  See the file COPYING for more details.
 */

#include <sys/types.h>
#include <asm/types.h>
#include <stdlib.h>

/*
 * There are multiple 16-bit CRC polynomials in common use, but this is
 * *the* standard CRC-32 polynomial, first popularized by Ethernet.
 * x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x^1+x^0
 */
#define CRCPOLY_LE 0xedb88320
#define CRCPOLY_BE 0x04c11db7

/*
 * This is the CRC32c polynomial, as outlined by Castagnoli.
 * x^32+x^28+x^27+x^26+x^25+x^23+x^22+x^20+x^19+x^18+x^14+x^13+x^11+x^10+x^9+
 * x^8+x^6+x^0
 */
#define CRC32C_POLY_LE 0x82F63B78

/**
 * crc32_le_generic() - Calculate bitwise little-endian Ethernet AUTODIN II
 *			CRC32/CRC32C
 * @crc: seed value for computation.  ~0 for Ethernet, sometimes 0 for other
 *	 uses, or the previous crc32/crc32c value if computing incrementally.
 * @p: pointer to buffer over which CRC32/CRC32C is run
 * @len: length of buffer @p
 * @polynomial: CRC32/CRC32c LE polynomial
 */
static inline __u32 crc32_le_generic(__u32 crc, unsigned char const *p,
				     size_t len, __u32 polynomial)
{
	int i;
	while (len--) {
		crc ^= *p++;
		for (i = 0; i < 8; i++)
			crc = (crc >> 1) ^ ((crc & 1) ? polynomial : 0);
	}
	return crc;
}

__u32 crc32_le(__u32 crc, unsigned char const *p, size_t len)
{
	return crc32_le_generic(crc, p, len, CRCPOLY_LE);
}

__u32 crc32c_le(__u32 crc, unsigned char const *p, size_t len)
{
	return crc32_le_generic(crc, p, len, CRC32C_POLY_LE);
}

/**
 * crc32_be_generic() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
 * @crc: seed value for computation.  ~0 for Ethernet, sometimes 0 for
 *	other uses, or the previous crc32 value if computing incrementally.
 * @p: pointer to buffer over which CRC32 is run
 * @len: length of buffer @p
 * @polynomial: CRC32 BE polynomial
 */
static inline __u32 crc32_be_generic(__u32 crc, unsigned char const *p,
				     size_t len, __u32 polynomial)
{
	int i;
	while (len--) {
		crc ^= *p++ << 24;
		for (i = 0; i < 8; i++)
			crc =
			    (crc << 1) ^ ((crc & 0x80000000) ? polynomial :
					  0);
	}
	return crc;
}

__u32 crc32_be(__u32 crc, unsigned char const *p, size_t len)
{
	return crc32_be_generic(crc, p, len, CRCPOLY_BE);
}