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

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

[Roger Knecht]

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@norberthealth.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

Re: [PATCH RESEND v3] Trivial comment fix for the CRC ITU-T polynom

[Randy Dunlap]

On 8/31/21 6:07 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@norberthealth.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,


I should have noticed this earlier:

Please change the /** to a simple /*.
/** means "beginning of kernel-doc comment" and this is not
a kernel-doc comment.

Thanks.

-- 
~Randy

Re: [PATCH RESEND v3] Trivial comment fix for the CRC ITU-T polynom

[Roger Knecht]

Hi Randy,

No problem, I will update the patch.

Regards,
Roger