converse.js/src/shared/qrcode/polynomial.js

Browser based XMPP chat client

class QRPolynomial {
    constructor(num, shift) {
        if (num.length == undefined) {
            throw new Error(num.length + "/" + shift);
        }
        let offset = 0;
        while (offset < num.length && num[offset] == 0) {
            offset++;
        }
        this.num = new Array(num.length - offset + shift);
        for (let i = 0; i < num.length - offset; i++) {
            this.num[i] = num[i + offset];
        }
    }

    get(index) {
        return this.num[index];
    }

    getLength() {
        return this.num.length;
    }

    multiply(e) {
        let num = new Array(this.getLength() + e.getLength() - 1);
        for (let i = 0; i < this.getLength(); i++) {
            for (let j = 0; j < e.getLength(); j++) {
                num[i + j] ^= QRMath.gexp(QRMath.glog(this.get(i)) + QRMath.glog(e.get(j)));
            }
        }
        return new QRPolynomial(num, 0);
    }

    mod(e) {
        if (this.getLength() - e.getLength() < 0) {
            return this;
        }
        let ratio = QRMath.glog(this.get(0)) - QRMath.glog(e.get(0));
        let num = new Array(this.getLength());
        for (let i = 0; i < this.getLength(); i++) {
            num[i] = this.get(i);
        }
        for (let i = 0; i < e.getLength(); i++) {
            num[i] ^= QRMath.gexp(QRMath.glog(e.get(i)) + ratio);
        }
        return new QRPolynomial(num, 0).mod(e);
    }
}

export default QRPolynomial;


export const QRMath = {
    glog: function (n) {
        if (n < 1) {
            throw new Error("glog(" + n + ")");
        }
        return QRMath.LOG_TABLE[n];
    },
    gexp: function (n) {
        while (n < 0) {
            n += 255;
        }
        while (n >= 256) {
            n -= 255;
        }
        return QRMath.EXP_TABLE[n];
    },
    EXP_TABLE: new Array(256),
    LOG_TABLE: new Array(256),
};

for (let i = 0; i < 8; i++) {
    QRMath.EXP_TABLE[i] = 1 << i;
}

for (let i = 8; i < 256; i++) {
    QRMath.EXP_TABLE[i] =
        QRMath.EXP_TABLE[i - 4] ^ QRMath.EXP_TABLE[i - 5] ^ QRMath.EXP_TABLE[i - 6] ^ QRMath.EXP_TABLE[i - 8];
}

for (let i = 0; i < 255; i++) {
    QRMath.LOG_TABLE[QRMath.EXP_TABLE[i]] = i;
}