public Projective EcTwinMult(BigInt d0, Projective S, BigInt d1, Projective T)
{
var d = new BigInt[2] { d0, d1 };
var SpT = EcFullAdd(S, T);
var SmT = EcFullSub(S, T);
var m0 = d0.BitCount();
var m1 = d1.BitCount();
var m = Math.Max(m0, m1);
var c = new int[2][];
c[0] = new int[6] { 0, 0, d0.BitAt(m - 1) ? 1 : 0, d0.BitAt(m - 2) ? 1 : 0, d0.BitAt(m - 3) ? 1 : 0, d0.BitAt(m - 4) ? 1 : 0 };
c[1] = new int[6] { 0, 0, d1.BitAt(m - 1) ? 1 : 0, d1.BitAt(m - 2) ? 1 : 0, d1.BitAt(m - 3) ? 1 : 0, d1.BitAt(m - 4) ? 1 : 0 };
var R = new Projective() { x = new BigInt(1, S.x.Length), y = new BigInt(1, S.x.Length), z = new BigInt(0, S.x.Length) };
int[] h = new int[2], u = new int[2];
for (var k = m; k >= 0; k--)
{
for (var i = 0; i <= 1; i++)
{
h[i] = (c[i][1] << 4) + (c[i][2] << 3) + (c[i][3] << 2) + (c[i][4] << 1) + c[i][5];
if (c[i][0] == 1)
h[i] = 31 - h[i];
}
for (var i = 0; i <= 1; i++)
{
var t = h[1 - i];
int f;
if (18 <= t && t < 22)
f = 9;
else if (14 <= t && t < 18)
f = 10;
else if (22 <= t && t < 24)
f = 11;
else if (4 <= t && t < 12)
f = 14;
else
f = 12;
if (h[i] < f)
u[i] = 0;
else
u[i] = (c[i][0] & 1) != 0 ? -1 : 1;
}
for (var i = 0; i < 2; i++)
{
c[i][0] = ((u[i] != 0) ^ (c[i][1] != 0)) ? 1 : 0;
c[i][1] = c[i][2];
c[i][2] = c[i][3];
c[i][3] = c[i][4];
c[i][4] = c[i][5];
c[i][5] = d[i].BitAt(k - 5) ? 1 : 0;
}
R = EcDouble(R);
if (u[0] == -1)
{
if (u[1] == -1)
R = EcFullSub(R, SpT);
else if (u[1] == 0)
R = EcFullSub(R, S);
else
R = EcFullSub(R, SmT);
}
else if (u[0] == 0)
{
if (u[1] == -1)
R = EcFullSub(R, T);
else if (u[1] == 1)
R = EcFullAdd(R, T);
}
else if (u[0] == 1)
{
if (u[1] == -1)
R = EcFullAdd(R, SmT);
else if (u[1] == 0)
R = EcFullAdd(R, S);
else
R = EcFullAdd(R, SpT);
}
}
return R;
}