Added error for ambiguous oid prefixes. Added methods to compare the first nth…

Added error for ambiguous oid prefixes. Added methods to compare the first nth hexadecimal characters (i.e. packets of 4 bits) of OIDs.

include/git2/errors.h

@@ -119,6 +119,9 @@ typedef enum {
 
 	/** The specified object has its data corrupted */
 	GIT_EOBJCORRUPTED = -28,
+
+	/** The given short oid is ambiguous */
+	GIT_EAMBIGUOUSOIDPREFIX = -29,
 } git_error;
 
 /**

include/git2/oid.h

@@ -133,6 +133,16 @@ GIT_EXTERN(void) git_oid_cpy(git_oid *out, const git_oid *src);
 GIT_EXTERN(int) git_oid_cmp(const git_oid *a, const git_oid *b);
 
 /**
+ * Compare the first 'len' hexadecimal characters (packets of 4 bits)
+ * of two oid structures.
+ * @param len the number of hex chars to compare
+ * @param a first oid structure.
+ * @param b second oid structure.
+ * @return 1 in case of a match
+ */
+GIT_EXTERN(int) gid_oid_match(unsigned int len, git_oid *a, git_oid *b);
+
+/**
  * OID Shortener object
  */
 typedef struct git_oid_shorten git_oid_shorten;

src/cache.h

@@ -42,6 +42,11 @@ GIT_INLINE(int) git_cached_obj_compare(git_cached_obj *obj, const git_oid *oid)
 	return git_oid_cmp(&obj->oid, oid);
 }
 
+GIT_INLINE(int) git_cached_obj_match(unsigned int len, git_cached_obj *obj, const git_oid *oid)
+{
+	return git_oid_match(len, &obj->oid, oid);
+}
+
 GIT_INLINE(void) git_cached_obj_incref(git_cached_obj *obj)
 {
 	git_atomic_inc(&obj->refcount);

src/errors.c

@@ -61,6 +61,7 @@ static struct {
 	{GIT_EEXISTS, "A reference with this name already exists"},
 	{GIT_EOVERFLOW, "The given integer literal is too large to be parsed"},
 	{GIT_ENOTNUM, "The given literal is not a valid number"},
+	{GIT_EAMBIGUOUSOIDPREFIX, "The given oid prefix is ambiguous"},
 };
 
 const char *git_strerror(int num)

src/oid.c

@@ -173,6 +173,26 @@ int git_oid_cmp(const git_oid *a, const git_oid *b)
 }
 
 
+int git_oid_match_raw(unsigned int len, const unsigned char *a, const unsigned char *b)
+{
+        do {
+                if (*a != *b)
+                        return 0;
+                a++;
+                b++;
+                len -= 2;
+        } while (len > 1);
+        if (len)
+                if ((*a ^ *b) & 0xf0)
+                        return 0;
+        return 1;
+}
+
+int gid_oid_match(unsigned int len, git_oid *a, git_oid *b)
+{
+	return git_oid_match_raw(len, a->id, b->id);
+}
+
 typedef short node_index;
 
 typedef union {

src/oid.h

+#ifndef INCLUDE_oid_h__
+#define INCLUDE_oid_h__
+
+/* This can be useful for internal use */
+int git_oid_match_raw(unsigned int len, const unsigned char *a, const unsigned char *b);
+
+#endif