ECP8.mul16 = function()

in src/ecp8.js [880:1050]
152 lines of code
11 McCabe index (conditional complexity)

    ECP8.mul16 = function(Q, u) {
        var W = new ECP8(),
            P = new ECP8(),
            T1 = [],
            T2 = [],
            T3 = [],
            T4 = [],
            mt = new ctx.BIG(),
            t = [],
            w1 = [],
            s1 = [],
            w2 = [],
            s2 = [],
            w3 = [],
            s3 = [],
            w4 = [],
            s4 = [],
            F=ECP8.frob_constants(),
            i, j, k, nb, bt, pb1, pb2, pb3, pb4;

        for (i = 0; i < 16; i++) {
            t[i] = new ctx.BIG(u[i]); t[i].norm();
            //Q[i].affine();
        }

        T1[0] = new ECP8(); T1[0].copy(Q[0]); // Q[0]
        T1[1] = new ECP8(); T1[1].copy(T1[0]); T1[1].add(Q[1]); // Q[0]+Q[1]
        T1[2] = new ECP8(); T1[2].copy(T1[0]); T1[2].add(Q[2]); // Q[0]+Q[2]
        T1[3] = new ECP8(); T1[3].copy(T1[1]); T1[3].add(Q[2]); // Q[0]+Q[1]+Q[2]
        T1[4] = new ECP8(); T1[4].copy(T1[0]); T1[4].add(Q[3]); // Q[0]+Q[3]
        T1[5] = new ECP8(); T1[5].copy(T1[1]); T1[5].add(Q[3]); // Q[0]+Q[1]+Q[3]
        T1[6] = new ECP8(); T1[6].copy(T1[2]); T1[6].add(Q[3]); // Q[0]+Q[2]+Q[3]
        T1[7] = new ECP8(); T1[7].copy(T1[3]); T1[7].add(Q[3]); // Q[0]+Q[1]+Q[2]+Q[3]

        //  Use Frobenius
        for (i=0;i<8;i++) {
            T2[i] = new ECP8(); T2[i].copy(T1[i]);
            T2[i].frob(F,4);
            T3[i] = new ECP8(); T3[i].copy(T2[i]);
            T3[i].frob(F,4);
            T4[i] = new ECP8(); T4[i].copy(T3[i]);
            T4[i].frob(F,4);
        }

        // Make it odd
        pb1=1-t[0].parity();
        t[0].inc(pb1);
        t[0].norm();

        pb2=1-t[4].parity();
        t[4].inc(pb2);
        t[4].norm();

        pb3=1-t[8].parity();
        t[8].inc(pb3);
        t[8].norm();

        pb4=1-t[12].parity();
        t[12].inc(pb4);
        t[12].norm();

        // Number of bits
        mt.zero();
        for (i=0;i<16;i++) {
            mt.or(t[i]);
        }

        nb=1+mt.nbits();

        // Sign pivot
        s1[nb-1]=1;
        s2[nb-1]=1;
        s3[nb-1]=1;
        s4[nb-1]=1;
        for (i=0;i<nb-1;i++) {
            t[0].fshr(1);
            s1[i]=2*t[0].parity()-1;
            t[4].fshr(1);
            s2[i]=2*t[4].parity()-1;

            t[8].fshr(1);
            s3[i]=2*t[8].parity()-1;
            t[12].fshr(1);
            s4[i]=2*t[12].parity()-1;
        }

        // Recoded exponent
        for (i=0; i<nb; i++) {
            w1[i]=0;
            k=1;
            for (j=1; j<4; j++) {
                bt=s1[i]*t[j].parity();
                t[j].fshr(1);
                t[j].dec(bt>>1);
                t[j].norm();
                w1[i]+=bt*k;
                k*=2;
            }
            w2[i]=0;
            k=1;
            for (j=5; j<8; j++) {
                bt=s2[i]*t[j].parity();
                t[j].fshr(1);
                t[j].dec(bt>>1);
                t[j].norm();
                w2[i]+=bt*k;
                k*=2;
            }

            w3[i]=0;
            k=1;
            for (j=9; j<12; j++) {
                bt=s3[i]*t[j].parity();
                t[j].fshr(1);
                t[j].dec(bt>>1);
                t[j].norm();
                w3[i]+=bt*k;
                k*=2;
            }
            w4[i]=0;
            k=1;
            for (j=13; j<16; j++) {
                bt=s4[i]*t[j].parity();
                t[j].fshr(1);
                t[j].dec(bt>>1);
                t[j].norm();
                w4[i]+=bt*k;
                k*=2;
            }
        }

        // Main loop
        P.select(T1,2*w1[nb-1]+1);
        W.select(T2,2*w2[nb-1]+1);
        P.add(W);
        W.select(T3,2*w3[nb-1]+1);
        P.add(W);
        W.select(T4,2*w4[nb-1]+1);
        P.add(W);
        for (i=nb-2;i>=0;i--) {
            P.dbl();
            W.select(T1,2*w1[i]+s1[i]);
            P.add(W);
            W.select(T2,2*w2[i]+s2[i]);
            P.add(W);
            W.select(T3,2*w3[i]+s3[i]);
            P.add(W);
            W.select(T4,2*w4[i]+s4[i]);
            P.add(W);
        }

        // apply correction
        W.copy(P);
        W.sub(Q[0]);
        P.cmove(W,pb1);

        W.copy(P);
        W.sub(Q[4]);
        P.cmove(W,pb2);

        W.copy(P);
        W.sub(Q[8]);
        P.cmove(W,pb3);

        W.copy(P);
        W.sub(Q[12]);
        P.cmove(W,pb4);

        P.affine();
        return P;
    };