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Commit 0cbaa448 authored by Jeremy Kerr's avatar Jeremy Kerr Committed by Greg Kroah-Hartman
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lib: Add crc4 module 



Add a little helper for crc4 calculations. This works 4-bits-at-a-time,
using a simple table approach.

We will need this in the FSI core code, as well as any master
implementations that need to calculate CRCs in software.

Signed-off-by: default avatarJeremy Kerr <jk@ozlabs.org>
Signed-off-by: default avatarChris Bostic <cbostic@linux.vnet.ibm.com>
Signed-off-by: default avatarJoel Stanley <joel@jms.id.au>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 414c1026

include/linux/crc4.h

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#ifndef _LINUX_CRC4_H

#define _LINUX_CRC4_H



#include <linux/types.h>



extern uint8_t crc4(uint8_t c, uint64_t x, int bits);



#endif /* _LINUX_CRC4_H */

lib/Kconfig

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@@ -158,6 +158,14 @@ config CRC32_BIT 


endchoice



config CRC4

	tristate "CRC4 functions"

	help

	  This option is provided for the case where no in-kernel-tree

	  modules require CRC4 functions, but a module built outside

	  the kernel tree does. Such modules that use library CRC4

	  functions require M here.



config CRC7

	tristate "CRC7 functions"

	help

lib/Makefile

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@@ -99,6 +99,7 @@ obj-$(CONFIG_CRC_T10DIF)+= crc-t10dif.o 
obj-$(CONFIG_CRC_ITU_T)	+= crc-itu-t.o

obj-$(CONFIG_CRC32)	+= crc32.o

obj-$(CONFIG_CRC32_SELFTEST)	+= crc32test.o

obj-$(CONFIG_CRC4)	+= crc4.o

obj-$(CONFIG_CRC7)	+= crc7.o

obj-$(CONFIG_LIBCRC32C)	+= libcrc32c.o

obj-$(CONFIG_CRC8)	+= crc8.o

lib/crc4.c

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/*

 * crc4.c - simple crc-4 calculations.

 *

 * This source code is licensed under the GNU General Public License, Version

 * 2. See the file COPYING for more details.

 */



#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.

 * @crc:  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");