The BigInt relational operators, for example BigInt::operator> are not optimal.

Currently, the code is:

bool BigInt::operator>(const BigInt& num) const { return !((*this < num) or (*this == num)); } 

This potentially makes two calls, one to operator< and another to operator ==. Only one call needs to be made:

bool BigInt::operator>(const BigInt& num) const { return *this < num; } 

The same issue with <=, where it takes just < to give the right results. Here is the corrected code:

 bool BigInt::operator<=(const BigInt& num) const { return !(num < *this); }