[PATCH 01/10] crc-itu-t: add bit-reversed calculation

Dmitry Eremin-Solenikov
2009-06-01T14:56:07Z

From: Darren Salt <linux@youmustbejoking.demon.co.uk>

Signed-off-by: Darren Salt <linux@youmustbejoking.demon.co.uk>
---
include/linux/crc-itu-t.h | 10 ++++++++++
lib/crc-itu-t.c | 18 ++++++++++++++++++
2 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/include/linux/crc-itu-t.h b/include/linux/crc-itu-t.h
index 84920f3..7b2b7ba 100644
--- a/include/linux/crc-itu-t.h
+++ b/include/linux/crc-itu-t.h
@@ -6,6 +6,9 @@
* Poly 0x0x1021 (x^16 + x^12 + x^15 + 1)
* Init 0
*
+ * The bit-reversed buffer variants may be non-standard, but some firmware
+ * loaders require them.
+ *
* This source code is licensed under the GNU General Public License,
* Version 2. See the file COPYING for more details.
*/
@@ -14,15 +17,22 @@
#define CRC_ITU_T_H

#include <linux/types.h>
+#include <linux/bitrev.h>

extern u16 const crc_itu_t_table[256];

extern u16 crc_itu_t(u16 crc, const u8 *buffer, size_t len);
+extern u16 crc_itu_t_bitreversed(u16 crc, const u8 *buffer, size_t len);

static inline u16 crc_itu_t_byte(u16 crc, const u8 data)
{
return (crc << 8) ^ crc_itu_t_table[((crc >> 8) ^ data) & 0xff];
}

+static inline u16 crc_itu_t_bitreversed_byte(u16 crc, const u8 data)
+{
+ return (crc << 8) ^ crc_itu_t_table[((crc >> 8) ^ bitrev8(data)) & 0xff];
+}
+
#endif /* CRC_ITU_T_H */

diff --git a/lib/crc-itu-t.c b/lib/crc-itu-t.c
index a63472b..5562fdd 100644
--- a/lib/crc-itu-t.c
+++ b/lib/crc-itu-t.c
@@ -64,6 +64,24 @@ u16 crc_itu_t(u16 crc, const u8 *buffer, size_t len)
}
EXPORT_SYMBOL(crc_itu_t);

+/**
+ * crc_itu_t_bitreversed - Compute the CRC-ITU-T for the data buffer;
+ * the buffer content is assumed to be bit-reversed
+ *
+ * @crc: previous CRC value
+ * @buffer: data pointer
+ * @len: number of bytes in the buffer
+ *
+ * Returns the updated CRC value
+ */
+u16 crc_itu_t_bitreversed(u16 crc, const u8 *buffer, size_t len)
+{
+ while (len--)
+ crc = crc_itu_t_bitreversed_byte(crc, *buffer++);
+ return crc;
+}
+EXPORT_SYMBOL(crc_itu_t_bitreversed);
+
MODULE_DESCRIPTION("CRC ITU-T V.41 calculations");
MODULE_LICENSE("GPL");

--
1.6.2.4