MODULE RandomSubtractiveFibo1;

Gnu CopyLefted.

Abstract: Pseudo-random number generator by Warren D. Smith.

IMPORT LongRealBasic AS R, RandomBasic;
IMPORT RandomRep;

<* UNUSED *>
CONST
  Module = "RandomImprovedMcGill.";

CONST
  asf1 = 97;
  bsf1 = 34;

REVEAL
  T = TPublic BRANDED OBJECT
        isf1 := asf1;
        jsf1 := bsf1;
        arrsf1: ARRAY [0 .. asf1 - 1] OF R.T;  (* initialize to rands in
                                                  [0,1) not all with LS
                                                  Bit=0*)
      OVERRIDES
        init   := Init;
        engine := Engine;
      END;

PROCEDURE Init (SELF: T; initrng: RandomBasic.T; ): T =
  VAR
  BEGIN
    FOR i := asf1 - 1 TO 0 BY -1 DO
      SELF.arrsf1[i] := initrng.generateReal();
    END;
    RETURN SELF;
  END Init;

PROCEDURE Engine (SELF: T; ): R.T =
  VAR x: R.T;
  BEGIN
    DEC(SELF.isf1);
    DEC(SELF.jsf1);
    IF SELF.isf1 < 0 THEN
      SELF.isf1 := asf1 - 1;     (* wraparound *)
    ELSIF SELF.jsf1 < 0 THEN
      SELF.jsf1 := asf1 - 1;     (* wraparound *)
    END;
    x := SELF.arrsf1[SELF.isf1] - SELF.arrsf1[SELF.jsf1];
    IF x < R.Zero THEN x := x + R.One; END; (* subtraction mod 1 *)
    SELF.arrsf1[SELF.isf1] := x;
    RETURN x;
  END Engine;

BEGIN
END RandomSubtractiveFibo1.