code: void copyValue(MutableBigInteger src) {
          int len = src.intLen;
          if (value.length < len)
              value = new int[len];
          System.arraycopy(src.value, src.offset, value, 0, len);
          intLen = len;
          offset = 0;
      }
docs: Sets this MutableBigInteger's value array to a copy of the specified
  array. The intLen is set to the length of the new array.