lib/crc7.c

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