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(* $Id: RandomNumbers.Mod,v 1.1 1997/02/07 07:45:32 oberon1 Exp $ *)
MODULE RandomNumbers;
(*
For details on this algorithm take a look at
Park S.K. and Miller K.W. (1988). Random number generators, good ones are
hard to find. Communications of the ACM, 31, 1192-1201.
*)
CONST
modulo* = 2147483647; (* =2^31-1 *)
VAR
z : LONGINT;
PROCEDURE GetSeed* (VAR seed : LONGINT);
(* Returns the currently used seed value. *)
BEGIN
seed := z
END GetSeed;
PROCEDURE PutSeed* (seed : LONGINT);
(* Set 'seed' as the new seed value. Any values for 'seed' are allowed, but
values beyond the intervall [1..2^31-2] will be mapped into this range. *)
BEGIN
seed := seed MOD modulo;
IF (seed = 0) THEN
z := 1
ELSE
z := seed
END
END PutSeed;
PROCEDURE NextRND;
CONST
a = 16807;
q = 127773; (* m div a *)
r = 2836; (* m mod a *)
VAR
lo, hi, test : LONGINT;
BEGIN
hi := z DIV q;
lo := z MOD q;
test := a * lo - r * hi;
IF (test > 0) THEN
z := test
ELSE
z := test + modulo
END
END NextRND;
PROCEDURE RND* (range : LONGINT) : LONGINT;
(* Calculates a new number. 'range' has to be in the intervall
[1..2^31-2]. Result is a number from 0,1,..,range-1. *)
BEGIN
NextRND;
RETURN z MOD range
END RND;
PROCEDURE Random*() : REAL;
(* Calculates a number x with 0.0 <= x < 1.0. *)
BEGIN
NextRND;
RETURN (z-1)*(1 / (modulo-1))
END Random;
(*
PROCEDURE Randomize*;
BEGIN
PutSeed (Unix.time (Unix.NULL))
END Randomize;
*)
BEGIN
z := 1
END RandomNumbers.
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