docs: public int nextSetBit(int fromIndex) {
          if(fromIndex < 0)
              throw new IndexOutOfBoundsException("fromIndex: " + fromIndex);
          if(fromIndex >= size)
              return -1;
  
          int u=wordIndex(fromIndex);
          long word=words[u] & (WORD_MASK << fromIndex);
  
          while(true) {
              if(word != 0)
                  return (u * BITS_PER_WORD) + Long.numberOfTrailingZeros(word);
              if(++u == words.length)
                  return -1;
              word=words[u];
          }
      }