linux-kernel - [PATCH RESEND v3] Trivial comment fix for the CRC ITU-T polynom

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Message-Id: <20210831130702.31526-1-roger@norberthealth.com>
Date:   Tue, 31 Aug 2021 15:07:02 +0200
From:   Roger Knecht <roger@...berthealth.com>
To:     Jiri Kosina <jkosina@...e.cz>,
        Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Jiri Kosina <trivial@...nel.org>, Jonathan Corbet <corbet@....net>,
        linux-doc@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Roger Knecht <roger@...berthealth.com>
Subject: [PATCH RESEND v3] Trivial comment fix for the CRC ITU-T polynom

This patch fixes a small typo in the CRC ITU-T polynom documentation.

The code comment says that the polynom is x^16 + x^12 + x^15 + 1, but the
correct polynom is x^16 + x^12 + x^5 + 1.

Quote from page 2 in the ITU-T V.41 specification:
  "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. [...]"

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

The hex polynom 0x1021 and CRC code implementation are correct.

Signed-off-by: Roger Knecht <roger@...berthealth.com>
---
Changes for the resend:
  - Moved "changes and thanks" out of the commit message.

Thanks,
Roger

 include/linux/crc-itu-t.h | 2 +-
 lib/crc-itu-t.c           | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/crc-itu-t.h b/include/linux/crc-itu-t.h
index a4367051e192..2f991a427ade 100644
--- a/include/linux/crc-itu-t.h
+++ b/include/linux/crc-itu-t.h
@@ -4,7 +4,7 @@
  *
  * Implements the standard CRC ITU-T V.41:
  *   Width 16
- *   Poly  0x1021 (x^16 + x^12 + x^15 + 1)
+ *   Poly  0x1021 (x^16 + x^12 + x^5 + 1)
  *   Init  0
  */
 
diff --git a/lib/crc-itu-t.c b/lib/crc-itu-t.c
index 1974b355c148..56e6e0d63d1e 100644
--- a/lib/crc-itu-t.c
+++ b/lib/crc-itu-t.c
@@ -7,7 +7,7 @@
 #include <linux/module.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] = {
 	0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
 	0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
-- 
2.17.1