Re: [PATCH v4] Trivial comment fix for the CRC ITU-T polynom

[Randy Dunlap]

On 8/31/21 8:11 AM, Roger Knecht wrote:
> 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@xxxxxxxxxxxxxxxxx>

Acked-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>


> ---
> Changes:
>    - Changed comment from /** to /* (the comment is not a kernel doc comment)

Roger, in future patches, you should do more like this under the --- line:

---
v4: <describe changes from v3 to v4>

v3: <describe changes from v2 to v3>

v2: <describe changes from v1 to v2>

I.e., keep a history of the version changes, not just the last change.

>   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,

thanks.
--
~Randy