lib/crc7.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *      crc7.c
   4  */
   5
   6 #include <linux/types.h>
   7 #include <linux/module.h>
   8 #include <linux/crc7.h>
   9
  10
  11 /*
  12  * Table for CRC-7 (polynomial x^7 + x^3 + 1).
  13  * This is a big-endian CRC (msbit is highest power of x),
  14  * aligned so the msbit of the byte is the x^6 coefficient
  15  * and the lsbit is not used.
  16  */
  17 const u8 crc7_be_syndrome_table[256] = {
  18         0x00, 0x12, 0x24, 0x36, 0x48, 0x5a, 0x6c, 0x7e,
  19         0x90, 0x82, 0xb4, 0xa6, 0xd8, 0xca, 0xfc, 0xee,
  20         0x32, 0x20, 0x16, 0x04, 0x7a, 0x68, 0x5e, 0x4c,
  21         0xa2, 0xb0, 0x86, 0x94, 0xea, 0xf8, 0xce, 0xdc,
  22         0x64, 0x76, 0x40, 0x52, 0x2c, 0x3e, 0x08, 0x1a,
  23         0xf4, 0xe6, 0xd0, 0xc2, 0xbc, 0xae, 0x98, 0x8a,
  24         0x56, 0x44, 0x72, 0x60, 0x1e, 0x0c, 0x3a, 0x28,
  25         0xc6, 0xd4, 0xe2, 0xf0, 0x8e, 0x9c, 0xaa, 0xb8,
  26         0xc8, 0xda, 0xec, 0xfe, 0x80, 0x92, 0xa4, 0xb6,
  27         0x58, 0x4a, 0x7c, 0x6e, 0x10, 0x02, 0x34, 0x26,
  28         0xfa, 0xe8, 0xde, 0xcc, 0xb2, 0xa0, 0x96, 0x84,
  29         0x6a, 0x78, 0x4e, 0x5c, 0x22, 0x30, 0x06, 0x14,
  30         0xac, 0xbe, 0x88, 0x9a, 0xe4, 0xf6, 0xc0, 0xd2,
  31         0x3c, 0x2e, 0x18, 0x0a, 0x74, 0x66, 0x50, 0x42,
  32         0x9e, 0x8c, 0xba, 0xa8, 0xd6, 0xc4, 0xf2, 0xe0,
  33         0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54, 0x62, 0x70,
  34         0x82, 0x90, 0xa6, 0xb4, 0xca, 0xd8, 0xee, 0xfc,
  35         0x12, 0x00, 0x36, 0x24, 0x5a, 0x48, 0x7e, 0x6c,
  36         0xb0, 0xa2, 0x94, 0x86, 0xf8, 0xea, 0xdc, 0xce,
  37         0x20, 0x32, 0x04, 0x16, 0x68, 0x7a, 0x4c, 0x5e,
  38         0xe6, 0xf4, 0xc2, 0xd0, 0xae, 0xbc, 0x8a, 0x98,
  39         0x76, 0x64, 0x52, 0x40, 0x3e, 0x2c, 0x1a, 0x08,
  40         0xd4, 0xc6, 0xf0, 0xe2, 0x9c, 0x8e, 0xb8, 0xaa,
  41         0x44, 0x56, 0x60, 0x72, 0x0c, 0x1e, 0x28, 0x3a,
  42         0x4a, 0x58, 0x6e, 0x7c, 0x02, 0x10, 0x26, 0x34,
  43         0xda, 0xc8, 0xfe, 0xec, 0x92, 0x80, 0xb6, 0xa4,
  44         0x78, 0x6a, 0x5c, 0x4e, 0x30, 0x22, 0x14, 0x06,
  45         0xe8, 0xfa, 0xcc, 0xde, 0xa0, 0xb2, 0x84, 0x96,
  46         0x2e, 0x3c, 0x0a, 0x18, 0x66, 0x74, 0x42, 0x50,
  47         0xbe, 0xac, 0x9a, 0x88, 0xf6, 0xe4, 0xd2, 0xc0,
  48         0x1c, 0x0e, 0x38, 0x2a, 0x54, 0x46, 0x70, 0x62,
  49         0x8c, 0x9e, 0xa8, 0xba, 0xc4, 0xd6, 0xe0, 0xf2
  50 };
  51 EXPORT_SYMBOL(crc7_be_syndrome_table);
  52
  53 /**
  54  * crc7_be - update the CRC7 for the data buffer
  55  * @crc:     previous CRC7 value
  56  * @buffer:  data pointer
  57  * @len:     number of bytes in the buffer
  58  * Context: any
  59  *
  60  * Returns the updated CRC7 value.
  61  * The CRC7 is left-aligned in the byte (the lsbit is always 0), as that
  62  * makes the computation easier, and all callers want it in that form.
  63  *
  64  */
  65 u8 crc7_be(u8 crc, const u8 *buffer, size_t len)
  66 {
  67         while (len--)
  68                 crc = crc7_be_byte(crc, *buffer++);
  69         return crc;
  70 }
  71 EXPORT_SYMBOL(crc7_be);
  72
  73 MODULE_DESCRIPTION("CRC7 calculations");
  74 MODULE_LICENSE("GPL");