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yap-6.3/docs/index/Benchmarks/compress.P

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abolish_table_info :- at(compress/2).
time :- statistics(runtime,_), benchmark, fail;
statistics(runtime,[_,T]), write(T).
benchmark :- data(Data), compress(Data, _C).
test :-
data(Data), reinit,
cputime(T0),
compress(Data, C), write(C), write(' '),
cputime(T1), T is T1-T0, write(T), write(' msecs'), nl, fail.
test.
%% data([a,a,b,a,a,b]).
%% data([a,a,b,a,a,b,a,a,b]).
%% data([a,a,a,a,a,a,a,a,a,a,a,a]).
%% data([a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a]).
%% data([a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a]).
%% data(D) :- bigdata(D).
%% data(D2) :- bigdata(D), append(D,D,D2).
data(D4) :- bigdata(D), append(D,D,D2), append(D2,D2,D4).
%% data(D8) :- bigdata(D), append(D,D,D2), append(D2,D2,D4), append(D4,D4,D8).
%% data(D16) :- bigdata(D), append(D,D,D2), append(D2,D2,D4), append(D4,D4,D8), append(D8,D8,D16).
bigdata([x,c,a,a,b,a,a,b,a,a,b,c,c,a,d,a,d,c,a,a,b,a,a,b,a,a,b,c,c,a,d,a,d,y]).
%% ==================== VERSION USING ASSERT FOR TABLES ======================
%% reinit :-
%% retractall(memo_compress(_, _)),
%% assert(memo_compress([C1], [C1])),
%% assert(memo_compress([C1,C2], [C1,C2])).
%%
%% compress(Initial, Compressed) :-
%% ( memo_compress(Initial, Compressed) -> true
%% mlength(Initial, LenInitial),
%% CurrentBest = Initial,
%% LenCurrentBest = LenInitial,
%% compress4(Initial, CurrentBest, LenCurrentBest, Compressed)
%% assert(memo_compress(Initial, Compressed))
%% ).
%% ===========================================================================
reinit :- abolish_all_tables.
:- table compress/2.
compress(Initial, Compressed) :-
mlength(Initial, LenInitial),
CurrentBest = Initial,
LenCurrentBest = LenInitial,
compress4(Initial, CurrentBest, LenCurrentBest, Compressed).
compress4(Initial, CurrentBest, LenCurrentBest, Compressed) :-
( compress_with_bound(Initial, LenCurrentBest, NewBest) ->
mlength(NewBest, NewLenBest),
compress4(Initial, NewBest, NewLenBest, Compressed)
; Compressed = CurrentBest
).
compress_with_bound(Initial, LenBound, Better) :-
repetition_compress(Initial, LenBound, Better).
compress_with_bound(Initial, LenBound, Better) :-
two_price_compress(Initial, LenBound, Better).
repetition_compress(Initial, LenBound, Better) :-
chopup(Initial, Piece, Repeated),
( Piece = [C] ->
Better = [C,Repeated]
; compress(Piece, CompressedPiece),
append(['('|CompressedPiece], [')',Repeated], Better)
),
mlength(Better, LenBetter),
LenBetter < LenBound.
two_price_compress(Initial, LenBound, Better) :-
append(Piece1, Piece2, Initial),
Piece1 \== [],
Piece2 \== [],
compress(Piece1, Compressed1),
mlength(Compressed1, LenCompressed1),
LenCompressed1 < LenBound,
compress(Piece2, Compressed2),
mlength(Compressed2, LenCompressed2),
LenCompressed1 + LenCompressed2 < LenBound,
append(Compressed1, Compressed2, Better).
chopup(List, Part, Repeated) :-
append(Part, Rest, List),
Part \== [],
Rest \== [],
count_parts(Rest, Part, 1, Repeated).
count_parts(Rest, Part, I, O) :-
( Rest == [] -> I = O
; append(Part, Rest1, Rest),
I1 is I+1,
count_parts(Rest1, Part, I1, O)
).
%%----------------------------------------------------------------------------
%% Utilities below
%%----------------------------------------------------------------------------
append([],L,L).
append([H|L1],L2,[H|L3]) :- append(L1,L2,L3).
mlength(L,N) :- mlength(L,0,N).
mlength([],N,N).
mlength([_|R],N0,N) :- N1 is N0+1, mlength(R,N1,N).