docs: public static int previousSetBit(long[] v, int start) {
      if(start < 0) {
        return -1;
      }
      int wordindex = start >>> LONG_LOG2_SIZE;
      if(wordindex >= v.length) {
        return magnitude(v) - 1;
      }
      // Initial word
      final int off = 63 - (start & LONG_LOG2_MASK);
      long cur = v[wordindex] & (LONG_ALL_BITS >>> off);
      for(;;) {
        if(cur != 0) {
          return wordindex * Long.SIZE + 63 - ((cur == LONG_ALL_BITS) ? 0 : Long.numberOfLeadingZeros(cur));
        }
        if(wordindex == 0) {
          return -1;
        }
        cur = v[--wordindex];
      }
    }