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A delete will now cause the proper collapse of cnodes into snodes up the tree to the root node.

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This commit is contained in:
Gregory Burd 2013-02-22 14:45:23 -05:00
parent e7ec1105eb
commit c5fa370609
1 changed files with 32 additions and 21 deletions
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53
src/hamt.erl
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@ -235,26 +235,43 @@ delete(Key, {hamt, Node}=T)
when is_binary(Key) ->
case delete_1(hash(Key), Key, Node, 0) of
not_found -> T;
delete -> {hamt, nil};
N -> {hamt, N}
{snode, Key, _} -> {hamt, nil};
{snode, _, _}=N -> {hamt, N};
{cnode, _, _}=N -> {hamt, N}
end.
delete_1(H, Key, {cnode, Bitmap, Nodes}=CNode, L)
delete_1(H, Key, {cnode, Bitmap, Nodes}, L)
when is_integer(L), L =< 30 ->
Bit = bitpos(H, L),
Idx = index(Bit, Bitmap),
case exists(Bit, Bitmap) of
true ->
case delete_1(H, Key, ba_get(Idx, Nodes), L + 5) of
not_found -> not_found;
delete -> delete_2(Key, Bit, CNode);
N -> {cnode, Bitmap, ba_set(Idx, N, Nodes)}
{cnode, _, _}=CN ->
{cnode, Bitmap, ba_set(Idx, CN, Nodes)};
{snode, Key, _} ->
case length(Nodes) of
2 ->
[{snode, _, _}=SN] = ba_del(Key, Nodes),
SN;
false ->
{cnode, (Bitmap bxor Bit), ba_del(Key, Nodes)}
end;
{snode, _, _}=SN ->
case length(Nodes) > 1 of
true ->
{cnode, Bitmap, ba_set(Idx, SN, Nodes)};
false ->
SN
end;
not_found ->
not_found
end;
false ->
not_found
end;
delete_1(_H, Key, {snode, Key, _}, _L) ->
delete;
delete_1(_H, Key, {snode, Key, _}=SN, _L) ->
SN;
delete_1(_H, _Key, {snode, _, _}, _L) ->
not_found;
delete_1(_H, Key, {lnode, List}, _L) ->
@ -267,16 +284,6 @@ delete_1(_H, Key, {lnode, List}, _L) ->
{snode, Key, lists:keyfind(Key, 2, List)}
end.
%% @doc This CNode only has 2 elements in it and one is about to be
%% be deleted, time to collapse this CNode into an SNode.
delete_2(Key, _Bit, {cnode, _Bitmap, Nodes})
when length(Nodes) =:= 2 ->
[{snode, _, _}=SN] = ba_del(Key, Nodes),
SN;
%% @doc Remove the right key and update the bitmap
delete_2(Key, Bit, {cnode, Bitmap, Nodes}) ->
{cnode, (Bitmap bxor Bit), ba_del(Key, Nodes)}.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-spec map(Function, Hamt1) -> Hamt2 when
@ -409,9 +416,13 @@ del_one_of_many_keys_test() ->
{hamt,{snode,<<"k2">>,<<"v2">>}}).
del_causes_cascading_cnode_collapse_test() ->
H = hamt:put([{<<X>>, <<X>>} || X <- lists:seq(1,5)], hamt:new()),
?assertEqual(hamt:delete(<<5>>, H),
hamt:put([{<<X>>, <<X>>} || X <- lists:seq(1,4)], hamt:new())).
?assertEqual(hamt:delete(<<5>>, hamt:put([{<<X>>, <<X>>} || X <- lists:seq(1,6)], hamt:new())),
{hamt,{cnode,17629440,
[{snode,<<3>>,<<3>>},
{snode,<<6>>,<<6>>},
{snode,<<1>>,<<1>>},
{snode,<<2>>,<<2>>},
{snode,<<4>>,<<4>>}]}}).
put_lots_test() ->
KVPs = [{<<X>>, <<X>>} || X <- lists:seq(1,10000)],