linux-kernel - Re: [PATCH v5] crc-itu-t: Fix typo in CRC ITU-T polynom comment

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Date:   Sat, 21 May 2022 08:44:41 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Roger Knecht <roger@...berthealth.com>,
        linux-kernel@...r.kernel.org, Ivo van Doorn <IvDoorn@...il.com>
Cc:     kernel-janitors@...r.kernel.org, linux-doc@...r.kernel.org,
        Kristian Hoegsberg <krh@...hat.com>,
        Stefan Richter <stefanr@...6.in-berlin.de>
Subject: Re: [PATCH v5] crc-itu-t: Fix typo in CRC ITU-T polynom comment

Hi Roger,

On 5/21/22 05:47, Roger Knecht wrote:
> 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>
> Acked-by: Randy Dunlap <rdunlap@...radead.org>

I don't know which maintainer will merge this since no one is Cc:ed on it.
You will probably need to choose some maintainer to send the patch to.

But let's add the people who merged the header file in the first place
for their comments/review. (done)

> ---
> Changes:
> v5: Clean up patch description and added acked-by
> v4: Changed comment from /** to /* (the comment is not a kernel doc comment)
> v3: Moved "changes and thanks" out of the commit message.
> v2: Extended patch description
> 
>  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..1d26a1647da5 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,

-- 
~Randy