next_index function

chash_diff

diff --git a/src/chash.erl b/src/chash.erl
index ecf0fb2..8aafb20 100644
--- a/src/chash.erl
+++ b/src/chash.erl
@@ -37,7 +37,7 @@
      successors/2,successors/3,
      predecessors/2,predecessors/3,
      contains_name/2,key_of/1,
-     merge_rings/2]).
+     merge_rings/2, next_index/2]).
     
 -define(RINGTOP, trunc(math:pow(2,160)-1)).  % SHA-1 space
 -include_lib("eunit/include/eunit.hrl").
@@ -133,6 +133,14 @@ ordered_from(Index, {NumPartitions, Nodes}) ->
     {A, B} = lists:split((IndexAsInt div Inc)+1, Nodes),
     B ++ A.
 
+% @doc Given an object key, return the next Index.
+% @spec next_index(Index :: index(), CHash :: chash()) -> [NodeEntry]
+next_index({Bucket, Key}, NumPartitions) ->
+    ChashKey = riak_core_util:chash_key({Bucket, Key}),
+    <<Index:160/integer>> = ChashKey,
+    Inc = ?RINGTOP div NumPartitions,
+    ((Index div Inc) + 1) * Inc.
+
 % @doc Given any term used to name an object, produce that object's key
 %      into the ring.  Two names with the same SHA-1 hash value are
 %      considered the same name.