code: private final void primitiveLeftShift(int n) {
          int[] val = value;
          int n2 = 32 - n;
          for (int i=offset, c=val[i], m=i+intLen-1; i < m; i++) {
              int b = c;
              c = val[i+1];
              val[i] = (b << n) | (c >>> n2);
          }
          val[offset+intLen-1] <<= n;
      }
docs: Left shift this MutableBigInteger n bits, where n is
  less than 32.
  Assumes that intLen > 0, n > 0 for speed