anchor.diff:        }
       } else {
         var last = buffer.length - shift - 1;
  -      var otherOffset = 1 + _offset - offset;
  +      var otherOffset = 1 + OFFSET - offset;
         for (var i = 0; i < last; i++) {
  -        result.buffer[i] = ((buffer[i + shift] >> offset) & _mask) |
  -            ((buffer[i + shift + 1] << otherOffset) & _mask);
  +        result.buffer[i] = ((buffer[i + shift] >> offset) & MASK) |
  +            ((buffer[i + shift + 1] << otherOffset) & MASK);
         }
         if (0 <= last) {
  -        result.buffer[last] = (buffer[buffer.length - 1] >> offset) & _mask;
  +        result.buffer[last] = (buffer[buffer.length - 1] >> offset) & MASK;
         }
       }
       return result;
     }
   }
  +
  +// Constants specific to mapping bits into a [UInt32List].
  +const int SHIFT = 5;
  +const int OFFSET = 31;
  +const int MASK = 0xffffffff;
  +const List<int> SET_MASK = const [
  +  1,
  +  2,
  +  4,
  +  8,
  +  16,
  +  32,
  +  64,
  +  128,
  +  256,
  +  512,
  +  1024,
  +  2048,
  +  4096,
  +  8192,
  +  16384,
  +  32768,
  +  65536,
  +  131072,
  +  262144,
  +  524288,
  +  1048576,
  +  2097152,
  +  4194304,
  +  8388608,
  +  16777216,
  +  33554432,
  +  67108864,
  +  134217728,
  +  268435456,
  +  536870912,
  +  1073741824,
  +  2147483648
  +];
  +const List<int> CLEAR_MASK = const [
  +  -2,
  +  -3,
  +  -5,
  +  -9,
  +  -17,
  +  -33,
  +  -65,
  +  -129,
  +  -257,
  +  -513,
  +  -1025,
  +  -2049,
  +  -4097,
  +  -8193,
  +  -16385,
  +  -32769,
  +  -65537,
  +  -131073,
  +  -262145,
  +  -524289,
  +  -1048577,
  +  -2097153,
  +  -4194305,
  +  -8388609,
  +  -16777217,
  +  -33554433,
  +  -67108865,
  +  -134217729,
  +  -268435457,
  +  -536870913,
  +  -1073741825,
  +  -2147483649
  +];
  
positive.code:   int count([bool expected = true]) {
      var tally = 0;
      for (var index = 0; index < length; index++) {
        var actual = (buffer[index >> _shift] & _setMask[index & _offset]) != 0;
        if (actual == expected) {
          tally++;
        }
  
negative.code:   /// current value.
    void flip(int index) {
      if (0 <= index && index < length) {
        buffer[index >> SHIFT] ^= SET_MASK[index & OFFSET];
      } else {
        throw new RangeError.range(index, 0, length);
      }
  