// 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()); }
}