:- compiler_options([xpp_on,ciao_directives]).

#include "thread_defs_xsb.h"

:- export random_pause/1, mt_random/3, mt_random/1, mt_srand/0, for/3.

:- import mt_random_request/3 from machine.

:- comment(random_pause/1,"This predicate randomly sleeps between 0
and N units of time, where the unit of time is the time taken to
execute 1 loop of @tt{bebusy/1}.").

random_pause(N):- 
	mt_random_interval(N,R),
	bebusy(R).

%-----------------------------------------------------------------------
% random(+L, +U, -R) binds R to a random integer in [L,U) when L and U
% are integers, or to a random floating number in [L,U) otherwise.
%-----------------------------------------------------------------------

mt_random_interval(Num, R) :-
	Num1 is 2 * Num,		% linux hack since random is signed.
	mt_random_request(MT_RANDOM_INTERVAL,Num1,R).

mt_srand:- 
	mt_random_request(INIT_MT_RANDOM,_,_).

mt_random(Num):- 
	mt_random_request(MT_RANDOM,Num,_).
	
:- comment(mt_bebusy/1, "This predicate is used to allow pausing for
periods of time shorter than supported by the system call sleep/1.
machine_dependent_factor/1 is scaled to the number of iterations
required for 1 milliseconds of cputime to elapse (on my machine).  It
cannot support exact timings, of course, but may be useful for varying
thread testing.").

machine_dependent_factor(2000).

bebusy(0):- !.
bebusy(N):- 
	machine_dependent_factor(Factor),
	bebusy_1(Factor),
	N1 is N - 1,
	bebusy(N1).

bebusy_1(0):- !.
bebusy_1(N):- 
	N1 is N - 1,
	bebusy_1(N1).


%%% for(?I,+B1,+B2) nondeterministically binds I to all integer values
%%% from B1 to B2.  B1 and B2 must be integers, but either may be larger.
for(I,B1,B2) :-
	(B1 =< B2
	 ->	forup(I,B1,B2)
	 ;	fordown(I,B1,B2)
	).

forup(L,L,H) :- L =< H.
forup(I,L,H) :- L < H, L1 is L+1, forup(I,L1,H).

fordown(H,H,L) :- H >= L.
fordown(I,H,L) :- H > L, H1 is H-1, fordown(I,H1,L).