/* Program to do parallel quicksort.  Ben Moszkowski
  Initial version written around 29 Apr 84.
  Subsequent changes made.
  Updated 7 Feb 85.

  translate to Tokio by S.Kono
				Sun Aug 31 21:29:10 JST 1986
				using functor and implicit sync
  */

/* Support Routines */

'$function' (len(L) = Length :- functor(L,_,Length)).

'$function' (slice(List,From,To) = Slice
 :- Size<--To-From+1,From=From1,To=To1,
	(Size < 1, #(Slice = array) ; 
	#functor(Slice,array,Size),
	slice(1,List,From1,To1,1,Slice))).

slice(N,List,From,To,_,_) :- N>To,!.
slice(N,List,From,To,I,Slice) :- N>=From,!,
    NN = N+1,II = I+1,arg(N,List,E),arg(I,Slice,E),
    slice(NN,List,From,To,II,Slice).
slice(N,List,From,To,I,Slice) :-
    NN = N+1,
    slice(NN,List,From,To,I,Slice).

'$function' (thof(I,L) = E :- arg(I,L,E)).

fixed_list(Array,Length) :- L <-- Length,
	#functor(Array,array,L).

'$function' ( (if Cond then Yes else No) = Reply :-
    if Cond then Yes=Reply else No=Reply).


/* Support Routines end */

par_quicksort(L) :- 
    if len(L) =< 1
    then empty
    else 
	stable(Pivot),
	(   quick_partition(L,Pivot) &
	    sort_parts(L,Pivot) ).

quick_partition(L,Pivot) :- 
	I = 2, Z=1, J = len(L), J1=J+1,skip, 
	P = thof(1,L),
	partition(I,J1,P,Z,J,L,Pivot).

partition(K,K,P,I,J,L,Pivot) :- !,@Pivot=I,@I=I,@thof(I,L)=P.
partition(K,E,P,I,J,L,Pivot) :- thof(K,L) < P,!, II=I+1,
	@I=I, @thof(I,L) = thof(K,L), KK=K+1,
	partition(KK,E,P,II,J,L,Pivot).
partition(K,E,P,I,J,L,Pivot) :- JJ=J-1,
	@J=J, @thof(J,L) = thof(K,L), KK=K+1,
	partition(KK,E,P,I,JJ,L,Pivot).

sort_parts(L,Pivot) :- 
	stable(thof(Pivot,L)),
	quicksort_process(slice(L,1,       Pivot-1)),
	quicksort_process(slice(L,Pivot+1, len(L) )).
quicksort_process(L) :-
	par_quicksort(L) & stable(L).

monitor(L) :- 
	fixed_list(Tag_list,len(L)),
	#tag(1,len(L),L,Tag_list),
    	#((write('''List='''),write(L),put(" "),
	   write('''Tag_list='''),write(Tag_list))).

tag(I,J,_,_) :- I>J,!.
tag(I,K,L,T) :- (if I-1=thof(I,L) then 1 else 0) = thof(I,T),
	J=I+1,tag(J,K,L,T).

/*  test of quicksort */
sort_test(Init_vector) :- 
     %exists L : 
	stable(Init_vector),
        fixed_list(L,len(Init_vector)),
	L=Init_vector,
	par_quicksort(L),
%	#write(L).
	monitor(L).

sort_test1 :- array(2,0,1)=List,sort_test(List).

sort_test2 :-  array(2,4,9,1,0,10,6,8,7,5,3)=List,sort_test(List).

sort_test3 :- array(13,7,5,3,1,9,8,6,2,0,12,11,4,10)=List,sort_test(List).