Signed-off-by: Michael Haggerty <mhag...@alum.mit.edu>
---
 object.c | 29 ++++++++++++++++++++++++++++-
 object.h |  7 +++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/object.c b/object.c
index 584f7ac..57a0890 100644
--- a/object.c
+++ b/object.c
@@ -43,14 +43,32 @@ int type_from_string(const char *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;
+
+       /*
+        * 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));
-       /* Assumes power-of-2 hash sizes in grow_object_hash */
        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);
@@ -63,6 +81,10 @@ static void insert_obj_hash(struct object *obj, struct 
object **hash, unsigned i
        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;
@@ -92,6 +114,11 @@ struct object *lookup_object(const unsigned char *sha1)
        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;
diff --git a/object.h b/object.h
index dc5df8c..732bf4d 100644
--- 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);
 
+/*
+ * Return the current number of buckets in the object hashmap.
+ */
 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);
 
 /*
-- 
1.8.5.3

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