[U-Boot] [PATCH v3] lib:crc32:hash: 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
Changes for v3:
- Remove check on the output pointer
- As precaution, zero out the output buffer
---
 common/hash.c        |    6 ++++++
 include/hash.h       |    2 +-
 include/u-boot/crc.h |    3 ++-
 lib/crc32.c          |    3 ++-
 4 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/common/hash.c b/common/hash.c
index 7627b84..84c0a78 100644
--- a/common/hash.c
+++ b/common/hash.c
@@ -360,6 +360,12 @@ int hash_command(const char *algo_name, int flags, cmd_tbl_t *cmdtp, int flag,
 		u8 vsum[HASH_MAX_DIGEST_SIZE];
 		void *buf;
 
+		/*
+		 * This is a precaution for crc32, which allows output to be
+		 * overloaded to provide initial value of crc32.
+		 */
+		memset(output, 0, sizeof(output));
+
 		if (hash_lookup_algo(algo_name, &algo)) {
 			printf("Unknown hash algorithm '%s'\n", algo_name);
 			return CMD_RET_USAGE;
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..f57eb87 100644
--- a/lib/crc32.c
+++ b/lib/crc32.c
@@ -257,7 +257,8 @@ void crc32_wd_buf(const unsigned char *input, unsigned int ilen,
 {
 	uint32_t crc;
 
-	crc = crc32_wd(0, input, ilen, chunk_sz);
+	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