define utility functions for object IDs

There are several utility functions (hashcmp and friends) that are used
for comparing object IDs (SHA-1 values).  Using these functions, which
take pointers to unsigned char, with struct object_id requires tiresome
access to the sha1 member, which bloats code and violates the desired
encapsulation.  Provide wrappers around these functions for struct
object_id for neater, more maintainable code.  Use the new constants to
avoid the hard-coded 20s and 40s throughout the original functions.

These functions simply call the underlying pointer-to-unsigned-char
versions to ensure that any performance improvements will be passed
through to the new functions.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -718,13 +718,13 @@ extern char *sha1_pack_name(const unsigned char *sha1);
 extern char *sha1_pack_index_name(const unsigned char *sha1);
 
 extern const char *find_unique_abbrev(const unsigned char *sha1, int);
-extern const unsigned char null_sha1[20];
+extern const unsigned char null_sha1[GIT_SHA1_RAWSZ];
 
 static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
 {
 	int i;
 
-	for (i = 0; i < 20; i++, sha1++, sha2++) {
+	for (i = 0; i < GIT_SHA1_RAWSZ; i++, sha1++, sha2++) {
 		if (*sha1 != *sha2)
 			return *sha1 - *sha2;
 	}
@@ -732,20 +732,42 @@ static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
 	return 0;
 }
 
+static inline int oidcmp(const struct object_id *oid1, const struct object_id *oid2)
+{
+	return hashcmp(oid1->hash, oid2->hash);
+}
+
 static inline int is_null_sha1(const unsigned char *sha1)
 {
 	return !hashcmp(sha1, null_sha1);
 }
 
+static inline int is_null_oid(const struct object_id *oid)
+{
+	return !hashcmp(oid->hash, null_sha1);
+}
+
 static inline void hashcpy(unsigned char *sha_dst, const unsigned char *sha_src)
 {
-	memcpy(sha_dst, sha_src, 20);
+	memcpy(sha_dst, sha_src, GIT_SHA1_RAWSZ);
 }
+
+static inline void oidcpy(struct object_id *dst, const struct object_id *src)
+{
+	hashcpy(dst->hash, src->hash);
+}
+
 static inline void hashclr(unsigned char *hash)
 {
-	memset(hash, 0, 20);
+	memset(hash, 0, GIT_SHA1_RAWSZ);
 }
 
+static inline void oidclr(struct object_id *oid)
+{
+	hashclr(oid->hash);
+}
+
+
 #define EMPTY_TREE_SHA1_HEX \
 	"4b825dc642cb6eb9a060e54bf8d69288fbee4904"
 #define EMPTY_TREE_SHA1_BIN_LITERAL \
@@ -952,8 +974,10 @@ extern int for_each_abbrev(const char *prefix, each_abbrev_fn, void *);
  * null-terminated string.
  */
 extern int get_sha1_hex(const char *hex, unsigned char *sha1);
+extern int get_oid_hex(const char *hex, struct object_id *sha1);
 
 extern char *sha1_to_hex(const unsigned char *sha1);	/* static buffer result! */
+extern char *oid_to_hex(const struct object_id *oid);	/* same static buffer as sha1_to_hex */
 extern int read_ref_full(const char *refname, int resolve_flags,
 			 unsigned char *sha1, int *flags);
 extern int read_ref(const char *refname, unsigned char *sha1);

hex.c

@@ -38,7 +38,7 @@ const signed char hexval_table[256] = {
 int get_sha1_hex(const char *hex, unsigned char *sha1)
 {
 	int i;
-	for (i = 0; i < 20; i++) {
+	for (i = 0; i < GIT_SHA1_RAWSZ; i++) {
 		unsigned int val;
 		/*
 		 * hex[1]=='\0' is caught when val is checked below,
@@ -56,15 +56,20 @@ int get_sha1_hex(const char *hex, unsigned char *sha1)
 	return 0;
 }
 
+int get_oid_hex(const char *hex, struct object_id *oid)
+{
+	return get_sha1_hex(hex, oid->hash);
+}
+
 char *sha1_to_hex(const unsigned char *sha1)
 {
 	static int bufno;
-	static char hexbuffer[4][41];
+	static char hexbuffer[4][GIT_SHA1_HEXSZ + 1];
 	static const char hex[] = "0123456789abcdef";
 	char *buffer = hexbuffer[3 & ++bufno], *buf = buffer;
 	int i;
 
-	for (i = 0; i < 20; i++) {
+	for (i = 0; i < GIT_SHA1_RAWSZ; i++) {
 		unsigned int val = *sha1++;
 		*buf++ = hex[val >> 4];
 		*buf++ = hex[val & 0xf];
@@ -73,3 +78,8 @@ char *sha1_to_hex(const unsigned char *sha1)
 
 	return buffer;
 }
+
+char *oid_to_hex(const struct object_id *oid)
+{
+	return sha1_to_hex(oid->hash);
+}