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crc-itu-t: fix typo in CRC ITU-T polynomial comment

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The code comment says that the polynomial is x^16 + x^12 + x^15 + 1, but
the correct polynomial is x^16 + x^12 + x^5 + 1. Quoting from page 2 in
the ITU-T V.41 specification [1]:

  2 Encoding and checking process

  The service bits and information bits, taken in conjunction,
  correspond to the coefficients of a message polynomial having terms
  from x^(n-1) (n = total number of bits in a block or sequence) down to
  x^16. This polynomial is divided, modulo 2, by the generating
  polynomial x^16 + x^12 + x^5 + 1.

The hex (truncated) polynomial 0x1021 and CRC code implementation are
correct, however.

[1] https://www.itu.int/rec/T-REC-V.41-198811-I/en

Signed-off-by: Roger Knecht <roger@norberthealth.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
This commit is contained in:
Roger Knecht 2022-05-21 14:47:45 +02:00 committed by Jason A. Donenfeld
parent e71e60cd74
commit 7799164595
2 changed files with 2 additions and 2 deletions
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2
include/linux/crc-itu-t.h
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@ -4,7 +4,7 @@
* *
* Implements the standard CRC ITU-T V.41: * Implements the standard CRC ITU-T V.41:
* Width 16 * Width 16
* Poly 0x1021 (x^16 + x^12 + x^15 + 1) * Poly 0x1021 (x^16 + x^12 + x^5 + 1)
* Init 0 * Init 0
*/ */

2
lib/crc-itu-t.c
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@ -7,7 +7,7 @@
#include <linux/module.h> #include <linux/module.h>
#include <linux/crc-itu-t.h> #include <linux/crc-itu-t.h>
/** CRC table for the CRC ITU-T V.41 0x1021 (x^16 + x^12 + x^15 + 1) */ /* CRC table for the CRC ITU-T V.41 0x1021 (x^16 + x^12 + x^5 + 1) */
const u16 crc_itu_t_table[256] = { const u16 crc_itu_t_table[256] = {
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, 0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,