[U-Boot] [PATCH v2] lib:crc32: Allow setting of the initial crc32 value

[Lukasz Majewski]

The current approach set the initial value of crc32 calculation to zero,
which is correct for calculating checksum of the whole chunk of data.

It however, lacks the flexibility, when one wants to calculate CRC32 of
a file comprised of many smaller parts received separately.

In the proposed approach the output value is used as a starting condition
for the proper crc32 calculation at crc32_wd function. This behavior is
identical to the one provided by crc32() method implementation.

Additionally comments were appropriately updated.

Signed-off-by: Lukasz Majewski <l.majewski at samsung.com>
Cc: Marek Vasut <marex at denx.de>
---
Changes for v2:
- Replace casting from (u8*) to (u32*) with memcpy
---
 include/hash.h       |    2 +-
 include/u-boot/crc.h |    3 ++-
 lib/crc32.c          |    7 +++++--
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/hash.h b/include/hash.h
index dc21678..abf704d 100644
--- a/include/hash.h
+++ b/include/hash.h
@@ -101,7 +101,7 @@ int hash_command(const char *algo_name, int flags, cmd_tbl_t *cmdtp, int flag,
  * @algo_name:		Hash algorithm to use
  * @data:		Data to hash
  * @len:		Lengh of data to hash in bytes
- * @output:		Place to put hash value
+ * @output:		Place to put hash value - also the initial value (crc32)
  * @output_size:	On entry, pointer to the number of bytes available in
  *			output. On exit, pointer to the number of bytes used.
  *			If NULL, then it is assumed that the caller has
diff --git a/include/u-boot/crc.h b/include/u-boot/crc.h
index 754ac72..7a87911 100644
--- a/include/u-boot/crc.h
+++ b/include/u-boot/crc.h
@@ -19,7 +19,8 @@ uint32_t crc32_no_comp (uint32_t, const unsigned char *, uint);
  *
  * @input:	Input buffer
  * @ilen:	Input buffer length
- * @output:	Place to put checksum result (4 bytes)
+ * @output:	Place to provide initial CRC32 value and afterwards
+ *		put checksum result (4 bytes)
  * @chunk_sz:	Trigger watchdog after processing this many bytes
  */
 void crc32_wd_buf(const unsigned char *input, uint ilen,
diff --git a/lib/crc32.c b/lib/crc32.c
index 9759212..80e078f 100644
--- a/lib/crc32.c
+++ b/lib/crc32.c
@@ -255,9 +255,12 @@ uint32_t ZEXPORT crc32_wd (uint32_t crc,
 void crc32_wd_buf(const unsigned char *input, unsigned int ilen,
 		unsigned char *output, unsigned int chunk_sz)
 {
-	uint32_t crc;
+	uint32_t crc = 0;
 
-	crc = crc32_wd(0, input, ilen, chunk_sz);
+	if (*output)
+		memcpy(&crc, output, sizeof(crc));
+
+	crc = crc32_wd(crc, input, ilen, chunk_sz);
 	crc = htonl(crc);
 	memcpy(output, &crc, sizeof(crc));
 }
-- 
1.7.10.4