minix/lib/ack/libm2/random.mod

58 lines
1.1 KiB
Modula-2
Executable file

(*
(c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
See the copyright notice in the ACK home directory, in the file "Copyright".
*)
(*$R-*)
IMPLEMENTATION MODULE random;
(*
Module: random numbers
Author: Ceriel J.H. Jacobs
Version: $Header$
*)
FROM Unix IMPORT getpid, time;
TYPE index = [1..55];
VAR X: ARRAY index OF CARDINAL;
j, k: index;
tm: LONGINT;
PROCEDURE Random(): CARDINAL;
BEGIN
IF k-1 <= 0 THEN k := 55; ELSE DEC(k) END;
IF j-1 <= 0 THEN j := 55; ELSE DEC(j) END;
X[k] := X[k] + X[j];
RETURN X[k]
END Random;
PROCEDURE Uniform (lwb, upb: CARDINAL): CARDINAL;
BEGIN
IF upb <= lwb THEN RETURN lwb; END;
RETURN lwb + (Random() MOD (upb - lwb + 1));
END Uniform;
PROCEDURE StartSeed(seed: CARDINAL);
VAR v: CARDINAL;
BEGIN
FOR k := 1 TO 55 DO
seed := 1297 * seed + 123;
X[k] := seed;
END;
FOR k := 1 TO 15 DO
j := tm MOD 55D + 1D;
v := X[j];
tm := tm DIV 7D;
j := tm MOD 55D + 1D;
X[j] := v;
tm := tm * 3D;
END;
k := 1;
j := 25;
END StartSeed;
BEGIN
tm := time(NIL);
X[1] := tm;
StartSeed(CARDINAL(getpid()) * X[1]);
END random.