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
