const BigInteger BigInteger::operator-(const BigInteger &other) const {
if (Signum() != other.Signum()) {
return (Signum() == Positive ? Negate() : *this) + (other.Signum() == Positive ? other.Negate() : other);
}
if (*this > other) {
int iterationSize = std::max(Size(), other.Size());
unsigned short remainder = 0;
std::vector<unsigned short> digitVector;
for (int i = 0; i < iterationSize; i++) {
unsigned short selfDigit = i < Size() ? mDigits[i] : 0;
unsigned short otherDigit = i < other.Size() ? other.mDigits[i] : 0;
unsigned short toSubstract = otherDigit + remainder;
if (selfDigit >= toSubstract) {
digitVector.push_back(selfDigit - toSubstract);
remainder = 0;
} else {
digitVector.push_back((selfDigit + 10) - toSubstract);
remainder = 1;
}
}
while (digitVector.at(digitVector.size() - 1) == 0) {
digitVector.pop_back();
}
return BigInteger(Signum(), digitVector.size(), CopyOf(digitVector));
} else {
return (other - (*this)).Negate();
}
}
bool BigInteger::operator<(const BigInteger &other) const {
if (Signum() == Positive && other.Signum() == Negative) {
return false;
}
if (Signum() == Negative && other.Signum() == Positive) {
return true;
}
if (Size() < other.Size()) {
return Signum() == Positive;
}
if (Size() > other.Size()) {
return Signum() == Negative;
}
// size of the two are equal, and the sign is also equal
for (int i = 0; i < Size(); i++) {
unsigned short selfDigit = mDigits[i];
unsigned short otherDigit = other.mDigits[i];
if (selfDigit != otherDigit) {
return Signum() == Negative ? selfDigit > otherDigit : selfDigit < otherDigit;
}
}
return false;
}
bool BigInteger::operator==(const BigInteger &other) const {
if (Signum() != other.Signum()) {
return false;
}
if (Size() != other.Size()) {
return false;
}
for (int i = 0; i < Size(); i++) {
if (mDigits[i] != other.mDigits[i]) {
return false;
}
}
return true;
}
const BigInteger BigInteger::operator+(const BigInteger &other) const {
if (Signum() != other.Signum()) {
return *this - other;
}
int iterationSize = std::max(Size(), other.Size());
unsigned short remainder = 0;
std::vector<unsigned short> digitVector;
for (int i = 0; i < iterationSize; i++) {
unsigned short selfDigit = i < Size() ? mDigits[i] : 0;
unsigned short otherDigit = i < other.Size() ? other.mDigits[i] : 0;
unsigned short result = selfDigit + otherDigit + remainder;
remainder = (unsigned short) (result / 10);
digitVector.push_back(result % 10);
}
if (remainder != 0) {
digitVector.push_back(remainder);
}
return BigInteger(Signum(), digitVector.size(), CopyOf(digitVector));
}
