1%% ``Licensed under the Apache License, Version 2.0 (the "License");
2%% you may not use this file except in compliance with the License.
3%% You may obtain a copy of the License at
4%%
5%%     http://www.apache.org/licenses/LICENSE-2.0
6%%
7%% Unless required by applicable law or agreed to in writing, software
8%% distributed under the License is distributed on an "AS IS" BASIS,
9%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
10%% See the License for the specific language governing permissions and
11%% limitations under the License.
12%%
13%% The Initial Developer of the Original Code is Ericsson Utvecklings AB.
14%% Portions created by Ericsson are Copyright 1999, Ericsson Utvecklings
15%% AB. All Rights Reserved.''
16%%
17%%     $Id: mnesia_frag_old_hash.erl,v 1.1 2008/12/17 09:53:38 mikpe Exp $
18%%%----------------------------------------------------------------------
19%%% Purpose : Implements hashing functionality for fragmented tables
20%%%----------------------------------------------------------------------
21
22-module(mnesia_frag_old_hash).
23-behaviour(mnesia_frag_hash).
24
25%% Hashing callback functions
26-export([
27	 init_state/2,
28	 add_frag/1,
29	 del_frag/1,
30	 key_to_frag_number/2,
31	 match_spec_to_frag_numbers/2
32	]).
33
34-record(old_hash_state,
35	{n_fragments,
36	 next_n_to_split,
37	 n_doubles}).
38
39%% Old style. Kept for backwards compatibility.
40-record(frag_hash,
41	{foreign_key,
42	 n_fragments,
43	 next_n_to_split,
44	 n_doubles}).
45
46%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
47
48init_state(_Tab, InitialState) when InitialState == undefined ->
49    #old_hash_state{n_fragments     = 1,
50		    next_n_to_split = 1,
51		    n_doubles       = 0};
52init_state(_Tab, FH) when record(FH, frag_hash) ->
53    %% Old style. Kept for backwards compatibility.
54    #old_hash_state{n_fragments     = FH#frag_hash.n_fragments,
55		    next_n_to_split = FH#frag_hash.next_n_to_split,
56		    n_doubles       = FH#frag_hash.n_doubles}.
57
58%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
59
60add_frag(State) when record(State, old_hash_state) ->
61    SplitN = State#old_hash_state.next_n_to_split,
62    P = SplitN + 1,
63    L = State#old_hash_state.n_doubles,
64    NewN = State#old_hash_state.n_fragments + 1,
65    State2 = case trunc(math:pow(2, L)) + 1 of
66		 P2 when P2 == P ->
67		     State#old_hash_state{n_fragments = NewN,
68					  next_n_to_split = 1,
69					  n_doubles = L + 1};
70		 _ ->
71		     State#old_hash_state{n_fragments = NewN,
72					  next_n_to_split = P}
73	     end,
74    {State2, [SplitN], [NewN]}.
75
76%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
77
78del_frag(State) when record(State, old_hash_state) ->
79    P = State#old_hash_state.next_n_to_split - 1,
80    L = State#old_hash_state.n_doubles,
81    N = State#old_hash_state.n_fragments,
82    if
83	P < 1 ->
84	    L2 = L - 1,
85	    MergeN = trunc(math:pow(2, L2)),
86	    State2 = State#old_hash_state{n_fragments = N - 1,
87					  next_n_to_split = MergeN,
88					  n_doubles = L2},
89	    {State2, [N], [MergeN]};
90	true ->
91	    MergeN = P,
92	    State2 = State#old_hash_state{n_fragments = N - 1,
93					  next_n_to_split = MergeN},
94	    {State2, [N], [MergeN]}
95	end.
96
97%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
98
99key_to_frag_number(State, Key) when record(State, old_hash_state) ->
100    L = State#old_hash_state.n_doubles,
101    A = erlang:hash(Key, trunc(math:pow(2, L))),
102    P = State#old_hash_state.next_n_to_split,
103    if
104	A < P ->
105	    erlang:hash(Key, trunc(math:pow(2, L + 1)));
106	true ->
107	    A
108    end.
109
110%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
111
112match_spec_to_frag_numbers(State, MatchSpec) when record(State, old_hash_state) ->
113    case MatchSpec of
114	[{HeadPat, _, _}] when tuple(HeadPat), size(HeadPat) > 2 ->
115	    KeyPat = element(2, HeadPat),
116	    case has_var(KeyPat) of
117		false ->
118		    [key_to_frag_number(State, KeyPat)];
119		true ->
120		    lists:seq(1, State#old_hash_state.n_fragments)
121	    end;
122	_ ->
123	    lists:seq(1, State#old_hash_state.n_fragments)
124    end.
125
126has_var(Pat) ->
127    mnesia:has_var(Pat).
128