diff --git a/pack-revindex.c b/pack-revindex.c
index ecdde39cf4..0ca3b54b45 100644
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -203,3 +203,35 @@ struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs)
 
 	return p->revindex + pos;
 }
+
+int offset_to_pack_pos(struct packed_git *p, off_t ofs, uint32_t *pos)
+{
+	int ret;
+
+	if (load_pack_revindex(p) < 0)
+		return -1;
+
+	ret = find_revindex_position(p, ofs);
+	if (ret < 0)
+		return ret;
+	*pos = ret;
+	return 0;
+}
+
+uint32_t pack_pos_to_index(struct packed_git *p, uint32_t pos)
+{
+	if (!p->revindex)
+		BUG("pack_pos_to_index: reverse index not yet loaded");
+	if (p->num_objects <= pos)
+		BUG("pack_pos_to_index: out-of-bounds object at %"PRIu32, pos);
+	return p->revindex[pos].nr;
+}
+
+off_t pack_pos_to_offset(struct packed_git *p, uint32_t pos)
+{
+	if (!p->revindex)
+		BUG("pack_pos_to_index: reverse index not yet loaded");
+	if (p->num_objects < pos)
+		BUG("pack_pos_to_offset: out-of-bounds object at %"PRIu32, pos);
+	return p->revindex[pos].offset;
+}
diff --git a/pack-revindex.h b/pack-revindex.h
index 848331d5d6..5a218aaa66 100644
--- a/pack-revindex.h
+++ b/pack-revindex.h
@@ -1,6 +1,21 @@
 #ifndef PACK_REVINDEX_H
 #define PACK_REVINDEX_H
 
+/**
+ * A revindex allows converting efficiently between three properties
+ * of an object within a pack:
+ *
+ * - index position: the numeric position within the list of sorted object ids
+ *   found in the .idx file
+ *
+ * - pack position: the numeric position within the list of objects in their
+ *   order within the actual .pack file (i.e., 0 is the first object in the
+ *   .pack, 1 is the second, and so on)
+ *
+ * - offset: the byte offset within the .pack file at which the object contents
+ *   can be found
+ */
+
 struct packed_git;
 
 struct revindex_entry {
@@ -8,9 +23,48 @@ struct revindex_entry {
 	unsigned int nr;
 };
 
+/*
+ * load_pack_revindex populates the revindex's internal data-structures for the
+ * given pack, returning zero on success and a negative value otherwise.
+ */
 int load_pack_revindex(struct packed_git *p);
 int find_revindex_position(struct packed_git *p, off_t ofs);
 
 struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs);
 
+/*
+ * offset_to_pack_pos converts an object offset to a pack position. This
+ * function returns zero on success, and a negative number otherwise. The
+ * parameter 'pos' is usable only on success.
+ *
+ * If the reverse index has not yet been loaded, this function loads it lazily,
+ * and returns an negative number if an error was encountered.
+ *
+ * This function runs in time O(log N) with the number of objects in the pack.
+ */
+int offset_to_pack_pos(struct packed_git *p, off_t ofs, uint32_t *pos);
+
+/*
+ * pack_pos_to_index converts the given pack-relative position 'pos' by
+ * returning an index-relative position.
+ *
+ * If the reverse index has not yet been loaded, or the position is out of
+ * bounds, this function aborts.
+ *
+ * This function runs in constant time.
+ */
+uint32_t pack_pos_to_index(struct packed_git *p, uint32_t pos);
+
+/*
+ * pack_pos_to_offset converts the given pack-relative position 'pos' into a
+ * pack offset. For a pack with 'N' objects, asking for position 'N' will return
+ * the total size (in bytes) of the pack.
+ *
+ * If the reverse index has not yet been loaded, or the position is out of
+ * bounds, this function aborts.
+ *
+ * This function runs in constant time.
+ */
+off_t pack_pos_to_offset(struct packed_git *p, uint32_t pos);
+
 #endif