Document some functions defined in object.c

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/object.c b/object.c
index 584f7acb36b68d17678b3fd6251105241794ea48..57a0890a87b66ea493337409606e57fd44d29f90 100644 (file)
--- a/object.c
+++ b/object.c
@@ -43,14 +43,32 @@ int type_from_string(const char *str)
        die("invalid object type \"%s\"", str);
 }
 
        die("invalid object type \"%s\"", str);
 }
 

+/*
+ * Return a numerical hash value between 0 and n-1 for the object with
+ * the specified sha1.  n must be a power of 2.  Please note that the
+ * return value is *not* consistent across computer architectures.
+ */

 static unsigned int hash_obj(const unsigned char *sha1, unsigned int n)
 {
        unsigned int hash;
 static unsigned int hash_obj(const unsigned char *sha1, unsigned int n)
 {
        unsigned int hash;

+
+       /*
+        * Since the sha1 is essentially random, we just take the
+        * required number of bits directly from the first
+        * sizeof(unsigned int) bytes of sha1.  First we have to copy
+        * the bytes into a properly aligned integer.  If we cared
+        * about getting consistent results across architectures, we
+        * would have to call ntohl() here, too.
+        */

        memcpy(&hash, sha1, sizeof(unsigned int));
        memcpy(&hash, sha1, sizeof(unsigned int));

-       /* Assumes power-of-2 hash sizes in grow_object_hash */

        return hash & (n - 1);
 }
 
        return hash & (n - 1);
 }
 

+/*
+ * Insert obj into the hash table hash, which has length size (which
+ * must be a power of 2).  On collisions, simply overflow to the next
+ * empty bucket.
+ */

 static void insert_obj_hash(struct object *obj, struct object **hash, unsigned int size)
 {
        unsigned int j = hash_obj(obj->sha1, size);
 static void insert_obj_hash(struct object *obj, struct object **hash, unsigned int size)
 {
        unsigned int j = hash_obj(obj->sha1, size);


@@ -63,6 +81,10 @@ static void insert_obj_hash(struct object *obj, struct object **hash, unsigned i
        hash[j] = obj;
 }
 
        hash[j] = obj;
 }
 

+/*
+ * Look up the record for the given sha1 in the hash map stored in
+ * obj_hash.  Return NULL if it was not found.
+ */

 struct object *lookup_object(const unsigned char *sha1)
 {
        unsigned int i, first;
 struct object *lookup_object(const unsigned char *sha1)
 {
        unsigned int i, first;


@@ -92,6 +114,11 @@ struct object *lookup_object(const unsigned char *sha1)
        return obj;
 }
 
        return obj;
 }
 

+/*
+ * Increase the size of the hash map stored in obj_hash to the next
+ * power of 2 (but at least 32).  Copy the existing values to the new
+ * hash map.
+ */

 static void grow_object_hash(void)
 {
        int i;
 static void grow_object_hash(void)
 {
        int i;

diff --git a/object.h b/object.h
index dc5df8ce1d9579a28477f91300aa7a49f37ad4e4..732bf4d7e7012ce56045ec52404ac92b077305a6 100644 (file)
--- a/object.h
+++ b/object.h
@@ -42,7 +42,14 @@ struct object {
 extern const char *typename(unsigned int type);
 extern int type_from_string(const char *str);
 
 extern const char *typename(unsigned int type);
 extern int type_from_string(const char *str);
 

+/*
+ * Return the current number of buckets in the object hashmap.
+ */

 extern unsigned int get_max_object_index(void);
 extern unsigned int get_max_object_index(void);

+
+/*
+ * Return the object from the specified bucket in the object hashmap.
+ */

 extern struct object *get_indexed_object(unsigned int);
 
 /*
 extern struct object *get_indexed_object(unsigned int);
 
 /*