code: public static boolean grpContains(byte[] gcmp, int offset, int idx) {
      if(offset < 0) throw new IndexOutOfBoundsException("offset < 0: " + offset);
      if(idx < offset) return false;
      idx = idx - offset;
      int max_idx = (gcmp.length << 3) - 1;
      if(idx > max_idx) return false;
  
      return (gcmp[idx >> 3] & ((byte)1 << (idx % 8))) != 0;
    }
docs: Return <code>true</code> if the given index is in given bit array else false.
  
  <p>The method returns <code>false</code> if <code>idx</code> is less than
  <code>offset</code>. It also returns <code>false</code> if the <code>idx</code>
  is greater then length of given bit set!
  </p>
  
  @param gcmp bit set array
  @param offset number of bits skipped by default since there are 0
  @param idx index of bit to be checked if it is in bitset
  @return