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Revert to two hash tiny bloom

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This commit is contained in:
Martin Sumner 2017-01-03 23:43:43 +00:00
parent 2f3eb18548
commit be1d678d85
1 changed files with 11 additions and 22 deletions
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33
src/leveled_tinybloom.erl
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@ -29,7 +29,6 @@
%%% Bloom API %%% Bloom API
%%%============================================================================ %%%============================================================================
empty(Width) when Width =< 256 -> empty(Width) when Width =< 256 ->
FoldFun = fun(X, Acc) -> dict:store(X, <<0:4096>>, Acc) end, FoldFun = fun(X, Acc) -> dict:store(X, <<0:4096>>, Acc) end,
lists:foldl(FoldFun, dict:new(), lists:seq(0, Width - 1)). lists:foldl(FoldFun, dict:new(), lists:seq(0, Width - 1)).
@ -37,7 +36,7 @@ empty(Width) when Width =< 256 ->
enter({hash, no_lookup}, Bloom) -> enter({hash, no_lookup}, Bloom) ->
Bloom; Bloom;
enter({hash, Hash}, Bloom) -> enter({hash, Hash}, Bloom) ->
{Slot0, Q, Bit1, Bit2, Bit3} = split_hash(Hash), {Slot0, Q, Bit1, Bit2} = split_hash(Hash),
Slot = Slot0 rem dict:size(Bloom), Slot = Slot0 rem dict:size(Bloom),
BitArray0 = dict:fetch(Slot, Bloom), BitArray0 = dict:fetch(Slot, Bloom),
{Pre, SplitArray0, Post} = split_array(BitArray0, Q), {Pre, SplitArray0, Post} = split_array(BitArray0, Q),
@ -45,7 +44,7 @@ enter({hash, Hash}, Bloom) ->
fun(Bit, Arr) -> add_to_array(Bit, Arr, 1024) end, fun(Bit, Arr) -> add_to_array(Bit, Arr, 1024) end,
SplitArray1 = lists:foldl(FoldFun, SplitArray1 = lists:foldl(FoldFun,
SplitArray0, SplitArray0,
lists:usort([Bit1, Bit2, Bit3])), [Bit1, Bit2]),
dict:store(Slot, <<Pre/binary, SplitArray1/binary, Post/binary>>, Bloom); dict:store(Slot, <<Pre/binary, SplitArray1/binary, Post/binary>>, Bloom);
enter(Key, Bloom) -> enter(Key, Bloom) ->
Hash = leveled_codec:magic_hash(Key), Hash = leveled_codec:magic_hash(Key),
@ -53,7 +52,7 @@ enter(Key, Bloom) ->
check({hash, Hash}, Bloom) -> check({hash, Hash}, Bloom) ->
{Slot0, Q, Bit1, Bit2, Bit3} = split_hash(Hash), {Slot0, Q, Bit1, Bit2} = split_hash(Hash),
Slot = Slot0 rem dict:size(Bloom), Slot = Slot0 rem dict:size(Bloom),
BitArray = dict:fetch(Slot, Bloom), BitArray = dict:fetch(Slot, Bloom),
{_Pre, SplitArray, _Post} = split_array(BitArray, Q), {_Pre, SplitArray, _Post} = split_array(BitArray, Q),
@ -66,12 +65,7 @@ check({hash, Hash}, Bloom) ->
<<0:1>> -> <<0:1>> ->
false; false;
<<1:1>> -> <<1:1>> ->
case getbit(Bit3, SplitArray, 1024) of true
<<0:1>> ->
false;
<<1:1>> ->
true
end
end end
end; end;
check(Key, Bloom) -> check(Key, Bloom) ->
@ -85,22 +79,17 @@ check(Key, Bloom) ->
split_hash(Hash) -> split_hash(Hash) ->
Slot = split_for_slot(Hash), Slot = split_for_slot(Hash),
{Q1, H1, H2, H3} = split_for_bits(Hash), {Q1, H1, H2} = split_for_bits(Hash),
{Slot, Q1, H1, H2, H3}. {Slot, Q1, H1, H2}.
split_for_slot(Hash) -> split_for_slot(Hash) ->
SlotH1 = Hash band 255, Hash band 255.
SlotH2 = (Hash bsr 8) band 255,
SlotH3 = (Hash bsr 16) band 255,
SlotH4 = (Hash bsr 24) band 255,
(SlotH1 bxor SlotH2) bxor (SlotH3 bxor SlotH4).
split_for_bits(Hash) -> split_for_bits(Hash) ->
Q1 = Hash band 3, H1 = (Hash bsr 8) band 1023,
H1 = (Hash bsr 2) band 1023, H2 = (Hash bsr 18) band 1023,
H2 = (Hash bsr 12) band 1023, Q1 = (Hash bsr 28) band 3,
H3 = (Hash bsr 22) band 1023, {Q1, H1, H2}.
{Q1, H1, H2, H3}.
split_array(Bin, Q) -> split_array(Bin, Q) ->
case Q of case Q of