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98576713ce
Estimated hours taken: 0.1 library/random.m: Change the coefficients for the linear-congruential generator. They now assume only 31 bits (unsigned) rather than 32. This should prevent the defective behaviour reported on the mercury-users mailing list.
109 lines
3.4 KiB
Mathematica
109 lines
3.4 KiB
Mathematica
%---------------------------------------------------------------------------%
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% Copyright (C) 1994-1998 The University of Melbourne.
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% This file may only be copied under the terms of the GNU Library General
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% Public License - see the file COPYING.LIB in the Mercury distribution.
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%---------------------------------------------------------------------------%
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%
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% file: rand.m
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% main author: conway
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% stability: low
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%
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% Define a set of random number generator predicates. This implementation
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% uses a threaded random-number supply. It could be made non-unique, but
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% since each thread returns the same list of random numbers, in the interests
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% of safety, it is declared with (backtrackable) unique modes.
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% The coefficients used in the implementation were taken from Numerical
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% Recipes in C (Press et al), and are originally due to Knuth.
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%
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%---------------------------------------------------------------------------%
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:- module random.
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:- interface.
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:- import_module list.
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% The type `random__supply' represents a supply of random numbers.
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:- type random__supply.
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% random__init(Seed, RS): creates a supply of random numbers RS
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% using the specified Seed.
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:- pred random__init(int, random__supply).
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:- mode random__init(in, uo) is det.
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% random__random(Num, RS0, RS): extracts a number Num in the
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% range 0 .. RandMax from the random number supply RS0, and
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% binds RS to the new state of the random number supply.
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:- pred random__random(int, random__supply, random__supply).
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:- mode random__random(out, mdi, muo) is det.
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% random__randmax(RandMax, RS0, RS): binds Randax to the maximum
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% random number that can be returned from the random number
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% supply RS0, and returns RS = RS0.
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:- pred random__randmax(int, random__supply, random__supply).
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:- mode random__randmax(out, mdi, muo) is det.
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%---------------------------------------------------------------------------%
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:- implementation.
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% Everything after the first `:- implementation' does not appear
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% in the Mercury Library Reference Manual.
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:- interface.
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% The following predicate was just for test purposes.
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% It should not be used by user programs.
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:- pragma obsolete(random__test/4).
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:- pred random__test(int, int, list(int), int).
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:- mode random__test(in, in, out, out) is det.
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%---------------------------------------------------------------------------%
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:- implementation.
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:- import_module int.
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:- type random__supply == int. % I(j)
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:- pred random__params(int, int, int). % a, c, m
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:- mode random__params(out, out, out) is det.
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random__params(9301, 49297, 233280).
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random__init(I0, RS) :-
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copy(I0, RS).
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random__random(I, RS0, RS) :-
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RS0 = I0,
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random__params(A, C, M),
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I is ((I0 * A) + C) mod M,
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copy(I, RS).
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random__randmax(M1, Rs, Rs) :-
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random__params(_A, _C, M),
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M1 is M - 1.
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%---------------------------------------------------------------------------%
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%---------------------------------------------------------------------------%
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random__test(Seed, N, Nums, Max) :-
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random__init(Seed, RS),
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random__randmax(Max, RS, RS1),
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random__test_2(N, Nums, RS1, _RS2).
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:- pred random__test_2(int, list(int), random__supply, random__supply).
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:- mode random__test_2(in, out, mdi, muo) is det.
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random__test_2(N, Is, RS0, RS) :-
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(
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N > 0
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->
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N1 is N - 1,
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random__random(I, RS0, RS1),
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random__test_2(N1, Is0, RS1, RS),
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Is = [I|Is0]
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;
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Is = [],
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RS = RS0
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).
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%---------------------------------------------------------------------------%
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