crc-itu-t: fix typo in CRC ITU-T polynomial comment

The code comment says that the polynomial is x^16 + x^12 + x^15 + 1, but
the correct polynomial is x^16 + x^12 + x^5 + 1. Quoting from page 2 in
the ITU-T V.41 specification [1]:

  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.

The hex (truncated) polynomial 0x1021 and CRC code implementation are
correct, however.

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

Signed-off-by: Roger Knecht <roger@norberthealth.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/include/linux/crc-itu-t.h b/include/linux/crc-itu-t.h
index a4367051e192c1c9abefb79fd7a5bf5413dfaeeb..2f991a427aded803da2bf7365662e18eb76451a3 100644 (file)
--- 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 1974b355c14862e810560b9565939caedff54c60..1d26a1647da537a2295bd3c036db430784f33a1c 100644 (file)
--- 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,