lib/crc7.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *      crc7.c
 */

#include <linux/types.h>
#include <linux/module.h>
#include <linux/crc7.h>

/*
 * Table for CRC-7 (polynomial x^7 + x^3 + 1).
 * This is a big-endian CRC (msbit is highest power of x),
 * aligned so the msbit of the byte is the x^6 coefficient
 * and the lsbit is not used.
 */
static const u8 crc7_be_syndrome_table[256] = {
	0x00, 0x12, 0x24, 0x36, 0x48, 0x5a, 0x6c, 0x7e,
	0x90, 0x82, 0xb4, 0xa6, 0xd8, 0xca, 0xfc, 0xee,
	0x32, 0x20, 0x16, 0x04, 0x7a, 0x68, 0x5e, 0x4c,
	0xa2, 0xb0, 0x86, 0x94, 0xea, 0xf8, 0xce, 0xdc,
	0x64, 0x76, 0x40, 0x52, 0x2c, 0x3e, 0x08, 0x1a,
	0xf4, 0xe6, 0xd0, 0xc2, 0xbc, 0xae, 0x98, 0x8a,
	0x56, 0x44, 0x72, 0x60, 0x1e, 0x0c, 0x3a, 0x28,
	0xc6, 0xd4, 0xe2, 0xf0, 0x8e, 0x9c, 0xaa, 0xb8,
	0xc8, 0xda, 0xec, 0xfe, 0x80, 0x92, 0xa4, 0xb6,
	0x58, 0x4a, 0x7c, 0x6e, 0x10, 0x02, 0x34, 0x26,
	0xfa, 0xe8, 0xde, 0xcc, 0xb2, 0xa0, 0x96, 0x84,
	0x6a, 0x78, 0x4e, 0x5c, 0x22, 0x30, 0x06, 0x14,
	0xac, 0xbe, 0x88, 0x9a, 0xe4, 0xf6, 0xc0, 0xd2,
	0x3c, 0x2e, 0x18, 0x0a, 0x74, 0x66, 0x50, 0x42,
	0x9e, 0x8c, 0xba, 0xa8, 0xd6, 0xc4, 0xf2, 0xe0,
	0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54, 0x62, 0x70,
	0x82, 0x90, 0xa6, 0xb4, 0xca, 0xd8, 0xee, 0xfc,
	0x12, 0x00, 0x36, 0x24, 0x5a, 0x48, 0x7e, 0x6c,
	0xb0, 0xa2, 0x94, 0x86, 0xf8, 0xea, 0xdc, 0xce,
	0x20, 0x32, 0x04, 0x16, 0x68, 0x7a, 0x4c, 0x5e,
	0xe6, 0xf4, 0xc2, 0xd0, 0xae, 0xbc, 0x8a, 0x98,
	0x76, 0x64, 0x52, 0x40, 0x3e, 0x2c, 0x1a, 0x08,
	0xd4, 0xc6, 0xf0, 0xe2, 0x9c, 0x8e, 0xb8, 0xaa,
	0x44, 0x56, 0x60, 0x72, 0x0c, 0x1e, 0x28, 0x3a,
	0x4a, 0x58, 0x6e, 0x7c, 0x02, 0x10, 0x26, 0x34,
	0xda, 0xc8, 0xfe, 0xec, 0x92, 0x80, 0xb6, 0xa4,
	0x78, 0x6a, 0x5c, 0x4e, 0x30, 0x22, 0x14, 0x06,
	0xe8, 0xfa, 0xcc, 0xde, 0xa0, 0xb2, 0x84, 0x96,
	0x2e, 0x3c, 0x0a, 0x18, 0x66, 0x74, 0x42, 0x50,
	0xbe, 0xac, 0x9a, 0x88, 0xf6, 0xe4, 0xd2, 0xc0,
	0x1c, 0x0e, 0x38, 0x2a, 0x54, 0x46, 0x70, 0x62,
	0x8c, 0x9e, 0xa8, 0xba, 0xc4, 0xd6, 0xe0, 0xf2
};

/**
 * crc7_be - update the CRC7 for the data buffer
 * @crc:     previous CRC7 value
 * @buffer:  data pointer
 * @len:     number of bytes in the buffer
 * Context: any
 *
 * Returns the updated CRC7 value.
 * The CRC7 is left-aligned in the byte (the lsbit is always 0), as that
 * makes the computation easier, and all callers want it in that form.
 *
 */
u8 crc7_be(u8 crc, const u8 *buffer, size_t len)
{
	while (len--)
		crc = crc7_be_syndrome_table[crc ^ *buffer++];
	return crc;
}
EXPORT_SYMBOL(crc7_be);

MODULE_DESCRIPTION("CRC7 calculations");
MODULE_LICENSE("GPL");