/* Return e.this+f.Q */
public ECP Mul2(BIG e, ECP Q, BIG f)
{
BIG te = new BIG();
BIG tf = new BIG();
BIG mt = new BIG();
ECP S = new ECP();
ECP T = new ECP();
ECP C = new ECP();
ECP[] W = new ECP[8];
sbyte[] w = new sbyte[1 + (BIG.NLEN * BIG.BASEBITS + 1) / 2];
int i, s, ns, nb;
sbyte a, b;
//affine();
//Q.affine();
te.Copy(e);
tf.Copy(f);
// precompute table
W[1] = new ECP();
W[1].Copy(this);
W[1].Sub(Q);
W[2] = new ECP();
W[2].Copy(this);
W[2].Add(Q);
S.Copy(Q);
S.Dbl();
W[0] = new ECP();
W[0].Copy(W[1]);
W[0].Sub(S);
W[3] = new ECP();
W[3].Copy(W[2]);
W[3].Add(S);
T.Copy(this);
T.Dbl();
W[5] = new ECP();
W[5].Copy(W[1]);
W[5].Add(T);
W[6] = new ECP();
W[6].Copy(W[2]);
W[6].Add(T);
W[4] = new ECP();
W[4].Copy(W[5]);
W[4].Sub(S);
W[7] = new ECP();
W[7].Copy(W[6]);
W[7].Add(S);
// if multiplier is odd, add 2, else add 1 to multiplier, and add 2P or P to correction
s = te.Parity();
te.Inc(1);
te.Norm();
ns = te.Parity();
mt.Copy(te);
mt.Inc(1);
mt.Norm();
te.CMove(mt, s);
T.CMove(this, ns);
C.Copy(T);
s = tf.Parity();
tf.Inc(1);
tf.Norm();
ns = tf.Parity();
mt.Copy(tf);
mt.Inc(1);
mt.Norm();
tf.CMove(mt, s);
S.CMove(Q, ns);
C.Add(S);
mt.Copy(te);
mt.Add(tf);
mt.Norm();
nb = 1 + (mt.NBits() + 1) / 2;
// convert exponent to signed 2-bit window
for (i = 0; i < nb; i++)
{
a = (sbyte)(te.LastBits(3) - 4);
te.Dec(a);
te.Norm();
te.FShr(2);
b = (sbyte)(tf.LastBits(3) - 4);
tf.Dec(b);
tf.Norm();
tf.FShr(2);
w[i] = (sbyte)(4 * a + b);
}
w[nb] = (sbyte)(4 * te.LastBits(3) + tf.LastBits(3));
S.Copy(W[(w[nb] - 1) / 2]);
for (i = nb - 1; i >= 0; i--)
{
T.Select(W, w[i]);
S.Dbl();
S.Dbl();
S.Add(T);
}
S.Sub(C); // apply correction
S.Affine();
return(S);
}
/* return e.this */
public ECP Mul(BIG e)
{
if (e.IsZilch() || IsInfinity())
{
return(new ECP());
}
ECP P = new ECP();
if (CURVETYPE == MONTGOMERY)
{
/* use Ladder */
int nb, i, b;
ECP D = new ECP();
ECP R0 = new ECP();
R0.Copy(this);
ECP R1 = new ECP();
R1.Copy(this);
R1.Dbl();
D.Copy(this);
D.Affine();
nb = e.NBits();
for (i = nb - 2; i >= 0; i--)
{
b = e.Bit(i);
P.Copy(R1);
P.DAdd(R0, D);
R0.CSwap(R1, b);
R1.Copy(P);
R0.Dbl();
R0.CSwap(R1, b);
}
P.Copy(R0);
}
else
{
// fixed size windows
int i, nb, s, ns;
BIG mt = new BIG();
BIG t = new BIG();
ECP Q = new ECP();
ECP C = new ECP();
ECP[] W = new ECP[8];
sbyte[] w = new sbyte[1 + (BIG.NLEN * BIG.BASEBITS + 3) / 4];
//affine();
// precompute table
Q.Copy(this);
Q.Dbl();
W[0] = new ECP();
W[0].Copy(this);
for (i = 1; i < 8; i++)
{
W[i] = new ECP();
W[i].Copy(W[i - 1]);
W[i].Add(Q);
}
// make exponent odd - add 2P if even, P if odd
t.Copy(e);
s = t.Parity();
t.Inc(1);
t.Norm();
ns = t.Parity();
mt.Copy(t);
mt.Inc(1);
mt.Norm();
t.CMove(mt, s);
Q.CMove(this, ns);
C.Copy(Q);
nb = 1 + (t.NBits() + 3) / 4;
// convert exponent to signed 4-bit window
for (i = 0; i < nb; i++)
{
w[i] = (sbyte)(t.LastBits(5) - 16);
t.Dec(w[i]);
t.Norm();
t.FShr(4);
}
w[nb] = (sbyte)t.LastBits(5);
P.Copy(W[(w[nb] - 1) / 2]);
for (i = nb - 1; i >= 0; i--)
{
Q.Select(W, w[i]);
P.Dbl();
P.Dbl();
P.Dbl();
P.Dbl();
P.Add(Q);
}
P.Sub(C); // apply correction
}
P.Affine();
return(P);
}
