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: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Chris Bostic <cbostic@linux.vnet.ibm.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jeremy Kerr 2017-06-06 16:08:39 -05:00 committed by Greg Kroah-Hartman
parent 414c102631
commit 0cbaa44841
4 changed files with 63 additions and 0 deletions

8
include/linux/crc4.h Normal file
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@ -0,0 +1,8 @@
#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 */

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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

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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

46
lib/crc4.c Normal file
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@ -0,0 +1,46 @@
/*
* 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");