ModulusPoly
ModulusPoly::add(const ModulusPoly& other) const
{
if (_field != other._field) {
throw std::invalid_argument("ModulusPolys do not have same ModulusGF field");
}
if (isZero()) {
return other;
}
if (other.isZero()) {
return *this;
}
auto smallerCoefficients = &_coefficients;
auto largerCoefficients = &other._coefficients;
if (smallerCoefficients->size() > largerCoefficients->size()) {
std::swap(smallerCoefficients, largerCoefficients);
}
std::vector<int> sumDiff(largerCoefficients->size());
size_t lengthDiff = largerCoefficients->size() - smallerCoefficients->size();
// Copy high-order terms only found in higher-degree polynomial's coefficients
std::copy_n(largerCoefficients->begin(), lengthDiff, sumDiff.begin());
for (size_t i = lengthDiff; i < largerCoefficients->size(); i++) {
sumDiff[i] = _field->add((*smallerCoefficients)[i - lengthDiff], (*largerCoefficients)[i]);
}
return ModulusPoly(*_field, sumDiff);
}
GF256Poly *GF256Poly::addOrSubtract(GF256Poly *b) {
if (&field != &b->field) {
throw IllegalArgumentException("Fields must be the same");
}
if (isZero()) {
return b;
}
if (b->isZero()) {
return this;
}
ArrayRef<int> largerCoefficients = coefficients;
ArrayRef<int> smallerCoefficients = b->coefficients;
if (smallerCoefficients.size() > largerCoefficients.size()) {
ArrayRef<int> tmp(smallerCoefficients);
smallerCoefficients = largerCoefficients;
largerCoefficients = tmp;
}
ArrayRef<int> sumDiff(new Array<int>(largerCoefficients.size()));
unsigned lengthDiff = largerCoefficients.size() - smallerCoefficients.size();
for (unsigned i = 0; i < lengthDiff; i++) {
sumDiff[i] = largerCoefficients[i];
}
for (unsigned i = lengthDiff; i < largerCoefficients.size(); i++) {
sumDiff[i] = GF256::addOrSubtract(smallerCoefficients[i - lengthDiff],
largerCoefficients[i]);
}
return new GF256Poly(field, sumDiff);
}