(* Minimal Standard Random Number Generator, from CACM October 1988 *)

(* Copyright (C)2018-2023, Philip Munts dba Munts Technologies.                *)
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IMPLEMENTATION MODULE Random;

  PROCEDURE rand(VAR seed : INTEGER) : REAL;

  CONST
    a = 16807;
    m = 2147483647;
    q = 127773;
    r = 2836;

  VAR
    lo   : INTEGER;
    hi   : INTEGER;
    test : INTEGER;

  BEGIN
    hi := seed DIV q;
    lo := seed MOD q;

    test := a*lo - r*hi;

    IF test > 0 THEN
      seed := test
    ELSE
      seed := test + m;
    END;

    RETURN FLOAT(seed)/FLOAT(m);
  END rand;

END Random.