Method ReedSolomonGenerator

Libraries/QRCode/tests/QrCode.cpp:567–589

qrcodegen::QrCode::ReedSolomonGenerator::ReedSolomonGenerator(int degree) :
		coefficients() {
	if (degree < 1 || degree > 255)
		throw "Degree out of range";
	
	// Start with the monomial x^0
	coefficients.resize(degree);
	coefficients.at(degree - 1) = 1;
	
	// Compute the product polynomial (x - r^0) * (x - r^1) * (x - r^2) * ... * (x - r^{degree-1}),
	// drop the highest term, and store the rest of the coefficients in order of descending powers.
	// Note that r = 0x02, which is a generator element of this field GF(2^8/0x11D).
	int root = 1;
	for (int i = 0; i < degree; i++) {
		// Multiply the current product by (x - r^i)
		for (size_t j = 0; j < coefficients.size(); j++) {
			coefficients.at(j) = multiply(coefficients.at(j), static_cast<uint8_t>(root));
			if (j + 1 < coefficients.size())
				coefficients.at(j) ^= coefficients.at(j + 1);
		}
		root = (root << 1) ^ ((root >> 7) * 0x11D);  // Multiply by 0x02 mod GF(2^8/0x11D)
	}
}


std::vector<uint8_t> qrcodegen::QrCode::ReedSolomonGenerator::getRemainder(const std::vector<uint8_t> &data) const {