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/*************************************************************************
* *
* YAP Prolog *
* *
* Yap Prolog was developed at NCCUP - Universidade do Porto *
* *
* Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997 *
* *
**************************************************************************
* *
* File: random.yap *
* Last rev: 5/12/99 *
* mods: *
* comments: Random operations *
* *
*************************************************************************/
% original code from RA O'Keefe.
% This is algorithm AS 183 from Applied Statistics. I also have a C
% version. It is really very good. It is straightforward to make a
% version which yields 15-bit random integers using only integer
% arithmetic.
:- module(random, [
random/1,
random/3,
randseq/3,
randset/3,
getrand/1,
setrand/1
]).
:- load_foreign_files([random], [], init_random).
% random(R) binds R to a new random number in [0.0,1.0)
% random(L, U, R) binds R to a random integer in [L,U)
% when L and U are integers (note that U will NEVER be generated),
% or to a random floating number in [L,U) otherwise.
random(L, U, R) :- integer(L), integer(U), !,
random(X),
R is L+integer((U-L)*X).
random(L, U, R) :-
number(L), number(U), !,
random(X),
R is L+((U-L)*X).
/* There are two versions of this operation.
randset(K, N, S)
generates a random set of K integers in the range 1..N.
The result is an ordered list, such as setof might produce.
randseq(K, N, L)
generates a random sequence of K integers, the order is as
random as we can make it.
*/
randset(K, N, S) :-
K >= 0,
K =< N,
randset(K, N, [], S).
randset(0, _, S, S) :- !.
randset(K, N, Si, So) :-
random(X),
X * N < K, !,
J is K-1,
M is N-1,
randset(J, M, [N|Si], So).
randset(K, N, Si, So) :-
M is N-1,
randset(K, M, Si, So).
randseq(K, N, S) :-
randseq(K, N, L, []),
keysort(L, R),
strip_keys(R, S).
randseq(0, _, S, S) :- !.
randseq(K, N, [Y-N|Si], So) :-
random(X),
X * N < K, !,
random(Y),
J is K-1,
M is N-1,
randseq(J, M, Si, So).
randseq(K, N, Si, So) :-
M is N-1,
randseq(K, M, Si, So).
strip_keys([], []) :- !.
strip_keys([_-K|L], [K|S]) :-
strip_keys(L, S).
setrand(rand(X,Y,Z)) :-
integer(X),
integer(Y),
integer(Z),
X > 0,
X < 30269,
Y > 0,
Y < 30307,
Z > 0,
Z < 30323,
setrand(X,Y,Z).
getrand(rand(X,Y,Z)) :-
getrand(X,Y,Z).
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