Big-int copy constructor unsafe

[reuk]

bigint.cc contains the following code:

BigInt &
BigInt::operator= (BigInt const &y)
{
  if (&y != this)
    {
      reallocate (y.length);
      length = y.length;
      positive = y.positive;
      memcpy (digit, y.digit, length * sizeof (onedig_t));
    }
  return *this;
}

inline void
BigInt::reallocate (unsigned digits)
{
  if (digits > size)
    {
      if (size)
        delete[] digit;
      size = adjust_size (digits);
      digit = new onedig_t[size];
    }
}

The problem is in these lines:

      size = adjust_size (digits);
      digit = new onedig_t[size];

If the call to new onedig_t[size] throws, then the object will be left in an invalid state in which the size is nonzero, even though digit doesn't point to a valid location.