/* Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@vu.nl WWW: http://www.swi-prolog.org Copyright (c) 2020, VU University Amsterdam CWI, Amsterdam All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ :- module(hashtable, [ ht_new/1, % --HT ht_is_hashtable/1, % @HT ht_size/2, % +HT, -Size ht_put/3, % !HT, +Key, +Value ht_update/4, % +HT, +Key, ?Old, +New ht_put_new/3, % !HT, +Key, +Value ht_put/5, % !HT, +Key, +Value, +IfNew, -Old ht_del/3, % !HT, +Key, -Value ht_get/3, % +HT, +Key, -Value ht_gen/3, % +HT, ?Key, ?Value ht_pairs/2, % ?HT, ?Pairs ht_keys/2 % +HT, -Keys ]). :- autoload(library(error), [must_be/2]). /** Hash tables Hash tables are one of the many key-value representations available to SWI-Prolog. This module implements a hash table as a _mutable_ and _backtrackable_ data structure. The hash table is implemented as a _closed hash table_, where the _buckets_ array is implemented using an unbounded arity compound term. Elements in this array are manipulated using setarg/3. Hash tables allow for any Prolog data types as keys or values, except that the key cannot be a variable. Applications that require a plain variable as key can do so by wrapping all keys in a compound, e.g., k(Var). */ /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Data structure ht(Load, Size, Table) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */ %! ht_new(--HT) % % Create a new hash table. ht_new(ht(0,0,[](_))). %! ht_is_hashtable(@HT) is semidet. % % True when HT is a hash table. ht_is_hashtable(HT) :- nonvar(HT), HT = ht(Load, Size, Buckets), integer(Load), integer(Size), compound_name_arity(Buckets, [], Arity), Arity =:= Size*2+1. %! ht_size(+HT, -Count) is det. % % True when Size is the number of key-value pairs in HT. ht_size(ht(Count, _Size, _Buckets), Count). %! ht_put(!HT, +Key, +Value) is det. % % Add a Key-Value to HT. The binding is undone on backtracking. ht_put(HT, Key, Value) :- must_be(nonvar, Key), ht_put(HT, Key, Value, _, _, _). %! ht_put_new(!HT, +Key, +Value) is semidet. % % As ht_put/3, but fails if Key is already in HT instead of updating % the associated value. ht_put_new(HT, Key, Value) :- must_be(nonvar, Key), ht_put(HT, Key, Value, _, _, true). %! ht_update(+HT, +Key, ?Old, +New) is semidet. % % True when HT holds Key-Old before and Key-New after this call. Note % that it is possible to update to a variable and the instantiate % this. For example, a word-count update could be implemented as: % % ``` % update_word_count(HT, Word) :- % ( ht_update(HT, Word, Old, New) % -> New is Old+1 % ; ht_put(HT, Word, 1) % ). % ``` ht_update(HT, Key, Old, New) :- must_be(nonvar, Key), ht_put(HT, Key, New, _, Old, false). %! ht_put(!HT, +Key, +Value, +IfNew, -Old) is det. % % Add Key-Value to HT. Old is unified with the old value associated % with Key or, if Key is new, with IfNew. This can be used to % bootstrap managing a list of values, e.g. % % ht_put_list(HT, Key, Value) :- % ht_put(HT, Key, [Value|Tail], [], Tail). ht_put(HT, Key, Value, IfNew, Old) :- must_be(nonvar, Key), ht_put(HT, Key, Value, IfNew, Old, _). ht_put(HT, Key, Value, IfNew, Old, IsNew) :- HT = ht(Load, Size, Buckets), ( Load >= Size//2 -> ht_resize(HT), ht_put(HT, Key, Value, IfNew, Old, IsNew) ; variant_hash(Key, I0), I is I0 mod Size, put_(Buckets, I, Size, Key, Old, IfNew, Value, IsNew), ( IsNew == true -> Load2 is Load+1, setarg(1, HT, Load2) ; true ) ). put_(Buckets, I, Size, Key, Old, IfNew, Value, IsNew) :- ht_kv(Buckets, I, K, V), ( var(K) -> IsNew = true, Old = IfNew, K = Key, V = Value ; K == Key -> IsNew = false, Old = V, ht_put_v(Buckets, I, Value) ; I2 is (I+1) mod Size, put_(Buckets, I2, Size, Key, Old, IfNew, Value, IsNew) ). ht_resize(HT) :- HT = ht(_Load, Size, Buckets), NewSize is max(4, Size*2), NewArity is NewSize*2+1, compound_name_arity(NewBuckets, [], NewArity), copy_members(0, Size, Buckets, NewSize, NewBuckets), setarg(2, HT, NewSize), setarg(3, HT, NewBuckets). copy_members(I, OSize, OBuckets, NSize, NBuckets) :- I < OSize, !, ht_kv(OBuckets, I, K, V), ( nonvar(K) -> variant_hash(K, I0), NI is I0 mod NSize, copy_(NBuckets, NI, NSize, K, V) ; true ), I2 is I+1, copy_members(I2, OSize, OBuckets, NSize, NBuckets). copy_members(_, _, _, _, _). copy_(Buckets, I, Size, Key, Value) :- ht_kv(Buckets, I, K, V), ( var(K) -> K = Key, V = Value ; I2 is (I+1) mod Size, copy_(Buckets, I2, Size, Key, Value) ). %! ht_del(!HT, +Key, -Value) is semidet. % % Delete Key-Value from HT. Fails if Key does not appear in HT or % Value does not unify with the old associated value. ht_del(HT, Key, Value) :- must_be(nonvar, Key), HT = ht(Load, Size, Buckets), Load > 0, variant_hash(Key, I0), I is I0 mod Size, del_(Buckets, I, Size, Key, Value), Load2 is Load - 1, setarg(1, HT, Load2). del_(Buckets, I, Size, Key, Value) :- ht_kv(Buckets, I, K, V), ( var(K) -> fail ; K == Key -> V = Value, ht_put_kv(Buckets, I, _, _), del_shift(Buckets, I, I, Size) ; I2 is (I+1) mod Size, del_(Buckets, I2, Size, Key, Value) ). del_shift(Buckets, I0, J, Size) :- I is (I0+1) mod Size, ht_kv(Buckets, I, K, V), ( var(K) -> true ; variant_hash(K, Hash), R is Hash mod Size, ( ( I >= R, R > J ; R > J, J > I ; J > I, I >= R ) -> del_shift(Buckets, I, J, Size) ; ht_put_kv(Buckets, J, K, V), ht_put_kv(Buckets, I, _, _), del_shift(Buckets, I, I, Size) ) ). %! ht_get(+HT, +Key, -Value) is semidet. % % True when Key is in HT and associated with Value. ht_get(ht(Load, Size, Buckets), Key, Value) :- Load > 0, must_be(nonvar, Key), variant_hash(Key, I0), I is I0 mod Size, get_(Buckets, I, Size, Key, Value). get_(Buckets, I, Size, Key, Value) :- ht_kv(Buckets, I, K, V), ( Key == K -> Value = V ; nonvar(K) -> I2 is (I+1) mod Size, get_(Buckets, I2, Size, Key, Value) ). ht_k(Buckets, I, K) :- IK is I*2+1, arg(IK, Buckets, K). ht_kv(Buckets, I, K, V) :- IK is I*2+1, IV is IK+1, arg(IK, Buckets, K), arg(IV, Buckets, V). ht_put_kv(Buckets, I, K, V) :- IK is I*2+1, IV is IK+1, setarg(IK, Buckets, K), setarg(IV, Buckets, V). ht_put_v(Buckets, I, V) :- IV is I*2+2, setarg(IV, Buckets, V). %! ht_gen(+HT, ?Key, ?Value) is nondet. % % True when Key-Value is in HT. Pairs are enumerated on backtracking % using the hash table order. ht_gen(HT, Key, Value) :- HT = ht(_, Size, Buckets), End is Size - 1, between(0, End, I), ht_kv(Buckets, I, K, V), nonvar(K), K = Key, V = Value. %! ht_pairs(?HT, ?Pairs) is det. % % True when Pairs and HT represent the same association. When used in % mode (+,-), Pairs is an ordered set. ht_pairs(HT, Pairs) :- ht_is_hashtable(HT), !, HT = ht(_Load, Size, Buckets), pairs_(0, Size, Buckets, Pairs0), sort(Pairs0, Pairs). ht_pairs(HT, Pairs) :- must_be(list(pair), Pairs), ht_new(HT), ht_fill(Pairs, HT). pairs_(I, Size, Buckets, Pairs) :- ( I < Size -> ht_kv(Buckets, I, K, V), ( nonvar(K) -> Pairs = [K-V|T], I2 is I+1, pairs_(I2, Size, Buckets, T) ; I2 is I+1, pairs_(I2, Size, Buckets, Pairs) ) ; Pairs = [] ). ht_fill([], _). ht_fill([K-V|T], HT) :- ht_put(HT, K, V), ht_fill(T, HT). %! ht_keys(+HT, -Keys) is det. % % True when Keys is an ordered set of all keys in HT. ht_keys(HT, Keys) :- HT = ht(_Load, Size, Buckets), keys_(0, Size, Buckets, Keys0), sort(Keys0, Keys). keys_(I, Size, Buckets, Keys) :- ( I < Size -> ht_k(Buckets, I, K), ( nonvar(K) -> Keys = [K|T], I2 is I+1, keys_(I2, Size, Buckets, T) ; I2 is I+1, keys_(I2, Size, Buckets, Keys) ) ; Keys = [] ).