// 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 LSFR {
  // 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, 0x6, 0xC, 0x14,
    0x30, 0x60, 0xB4, 0x110,
    0x240, 0x500, 0xE08, 0x1C80,
    0x3802, 0x6000, 0xD008, 0x12000,
    0x20400, 0x72000, 0x90000, 0x140000,
    0x300000, 0x420000, 0xE10000
  };
  
  *(int *n) {
    assertBetween(2, 24, n);
    cycleLength = (1 << n)-1;
    tap = tapTable[n-2];
  }
  
  int next() {
    if (++step == cycleLength) step = 0;
    
    int tapped = countBits(value & tap) & 1;
    ret value = (value >>> 1) | (tapped << n);
  }
  
  long nextLong() { ret uintToLong(next()); }
}