// maximum for n is 31 or 32

// (32 works but makes things a bit funky because you'll see negative

// integers as value, step count and cycle length. Unless you call the

// ...AsLong methods.)

// TODO: find tap tables for n=25 through 32

//       (so for now max is 24)

sclass SimpleLSFR {

  // params

  int n; // max 32

  int start = 1;

  // calculated

  int tap, cycleLength; // = 2^n-1

  // changing variables

  int step, value;

  // tap bit mask for different n's (2 through 24)

  static final int[] tapTable = {

    0x3, 0x3, 0x3, 0x5,

    0x3, 0x3, 0x2d, 0x11,

    0x9, 0x5, 0x107, 0x27,

    0x1007, 0x3, 0x100b, 0x9,

    0x81, 0x27, 0x9, 0x5,

    0x3, 0x21, 0x87

  };

  *(int *n) {

    assertBetween(2, 24, n);

    cycleLength = (1 << n)-1;

    tap = tapTable[n-2];

    value = start;

  }

  int next() {

    if (++step == cycleLength) step = 0;

    int tapped = (countBits(value & tap) & 1) ^ 1;

    ret value = (value >>> 1) | (tapped << (n-1));

  }

  // for debugging/visualization

  int tapped() { ret value & tap; }

  int tappedBitCount() { ret countBits(tapped()); }

  long nextLong() { ret uintToLong(next()); }

}