arithmetic/src/misc/stochastic/RandomQuaternaryFibo.m3

MODULE RandomQuaternaryFibo;
Gnu CopyLefted. 

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



IMPORT RandomBasic, Word;
IMPORT RandomRep;

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

CONST
  asf3 = 89;
  bsf3 = 57;
  csf3 = 14;
  dsf3 = 5;                      (* x^89 + x^57 + x^14 + x^5 + 1 primitive
                                    mod 2 *)

REVEAL
  T = TPublic BRANDED OBJECT
        isf3 := asf3;
        jsf3 := bsf3;
        ksf3 := csf3;
        msf3 := dsf3;
        arrsf3: ARRAY [0 .. asf3 - 1] OF Word.T;  (* initialize to random
                                                     words, not all even *)
      OVERRIDES
        init   := Init;
        engine := Engine;
      END;

PROCEDURE Init (SELF: T; initrng: RandomBasic.T; ): T =
  VAR
  BEGIN
    FOR i := asf3 - 1 TO 0 BY -1 DO
      SELF.arrsf3[i] := initrng.generateWord();
    END;
    SELF.arrsf3[0] := Word.Or(initrng.generateWord(), 2_1);
    RETURN SELF;
  END Init;

* Generates a new random Word.T; period at least 2^asf3 - 1;
 * uses both XOR and [- mod 2^wordsize] in the recurrence, hence may
 * avoid some of the known problems with each of these operations alone. 

PROCEDURE Engine (SELF: T; ): Word.T =
  VAR x: Word.T;
  BEGIN
    DEC(SELF.isf3);
    DEC(SELF.jsf3);
    DEC(SELF.ksf3);
    DEC(SELF.msf3);
    IF SELF.isf3 < 0 THEN
      SELF.isf3 := asf3 - 1;     (* wraparound *)
    ELSIF SELF.jsf3 < 0 THEN
      SELF.jsf3 := asf3 - 1;     (* wraparound *)
    ELSIF SELF.ksf3 < 0 THEN
      SELF.ksf3 := asf3 - 1;     (* wraparound *)
    ELSIF SELF.msf3 < 0 THEN
      SELF.msf3 := asf3 - 1;     (* wraparound *)
    END;
    x := Word.Minus(SELF.arrsf3[SELF.msf3],
                    Word.Xor(SELF.arrsf3[SELF.ksf3],
                             Word.Minus(SELF.arrsf3[SELF.isf3],
                                        SELF.arrsf3[SELF.jsf3])));
    SELF.arrsf3[SELF.isf3] := x;
    RETURN x;
  END Engine;

BEGIN
END RandomQuaternaryFibo.