linux-kernel - [PATCH] lib: crc32: crc32_generic_shift: fix comment on iteration count

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Message-ID: <87pp0843ye.fsf@gmail.com>
Date:	Wed, 21 Oct 2015 17:49:13 +0200
From:	Nicolai Stange <nicstange@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH] lib: crc32: crc32_generic_shift: fix comment on iteration count

In crc32_generic_shift(), the linear startup phase is commented
with a statement saying that "up to 32 bits" will be shifted in
a linear way.

However, the loop following that comment, namely

  for (i = 0; i < 8 * (int)(len & 3); i++) {...}

shifts only up to 8*3=24 bits.

Given the fact, that the binary method for exponentiation sets in
at 2^2*8=32, the loop's bounds are correct: it handles the cases
that any of the two least significant bits are set in len, i.e.
the cases 2^1*8 and 2^0*8 which sum to 24.

Fix the comment.

Signed-off-by: Nicolai Stange <nicstange@...il.com>
---
 lib/crc32.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/crc32.c b/lib/crc32.c
index 9a907d4..a1d17db 100644
--- a/lib/crc32.c
+++ b/lib/crc32.c
@@ -242,7 +242,7 @@ static u32 __attribute_const__ crc32_generic_shift(u32 crc, size_t len,
 	u32 power = polynomial;	/* CRC of x^32 */
 	int i;
 
-	/* Shift up to 32 bits in the simple linear way */
+	/* Shift up to 24 bits in the simple linear way */
 	for (i = 0; i < 8 * (int)(len & 3); i++)
 		crc = (crc >> 1) ^ (crc & 1 ? polynomial : 0);
 
-- 
2.6.1

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