hash: make is_null_oid() independent of the_repository

The function `is_null_oid()` uses `oideq(oid, null_oid())` to check
whether a given object ID is the all-zero object ID. `null_oid()`
implicitly relies on `the_repository` though to return the correct null
object ID.

Get rid of this dependency by always comparing the complete hash array
for being all-zeroes. This is possible due to the refactoring of object
IDs so that their hash arrays are always fully initialized.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

hash-ll.h

@@ -341,6 +341,12 @@ static inline unsigned int oidhash(const struct object_id *oid)
 	return hash;
 }
 
+static inline int is_null_oid(const struct object_id *oid)
+{
+	static const unsigned char null_hash[GIT_MAX_RAWSZ];
+	return !memcmp(oid->hash, null_hash, GIT_MAX_RAWSZ);
+}
+
 const char *empty_tree_oid_hex(void);
 const char *empty_blob_oid_hex(void);
 

hash.h

@@ -6,11 +6,6 @@
 
 #define the_hash_algo the_repository->hash_algo
 
-static inline int is_null_oid(const struct object_id *oid)
-{
-	return oideq(oid, null_oid());
-}
-
 static inline int is_empty_blob_oid(const struct object_id *oid)
 {
 	return oideq(oid, the_hash_algo->empty_blob);