private void karmul_upper(FF x, FF y, FF t, int n)
{ // Calculates Most Significant upper half of x*y, given lower part
int nd2;
nd2 = n / 2;
radd(n, x, 0, x, nd2, nd2);
radd(n + nd2, y, 0, y, nd2, nd2);
t.karmul(0, this, n + nd2, this, n, t, n, nd2); // t = (a0+a1)(b0+b1)
karmul(n, x, nd2, y, nd2, t, n, nd2); // z[n]= a1*b1
/* z[0-nd2]=l(a0b0) z[nd2-n]= h(a0b0)+l(t)-l(a0b0)-l(a1b1) */
t.rdec(0, this, n, n); // t=t-a1b1
rinc(nd2, this, 0, nd2); // z[nd2-n]+=l(a0b0) = h(a0b0)+l(t)-l(a1b1)
rdec(nd2, t, 0, nd2); // z[nd2-n]=h(a0b0)+l(t)-l(a1b1)-l(t-a1b1)=h(a0b0)
rnorm(0, -n); // a0b0 now in z - truncate it
t.rdec(0, this, 0, n); // (a0+a1)(b0+b1) - a0b0
rinc(nd2, t, 0, n);
rnorm(nd2, n);
}
/* z=x*y, t is workspace */
private void karmul(int vp, FF x, int xp, FF y, int yp, FF t, int tp, int n)
{
int nd2;
if (n == 1)
{
DBIG d = BIG.mul(x.v[xp], y.v[yp]);
v[vp + 1] = d.Split(8 * ROM.MODBYTES);
v[vp].copy(d);
return;
}
nd2 = n / 2;
radd(vp, x, xp, x, xp + nd2, nd2);
//rnorm(vp,nd2);
radd(vp + nd2, y, yp, y, yp + nd2, nd2);
//rnorm(vp+nd2,nd2);
t.karmul(tp, this, vp, this, vp + nd2, t, tp + n, nd2);
karmul(vp, x, xp, y, yp, t, tp + n, nd2);
karmul(vp + n, x, xp + nd2, y, yp + nd2, t, tp + n, nd2);
t.rdec(tp, this, vp, n);
t.rdec(tp, this, vp + n, n);
rinc(vp + nd2, t, tp, n);
rnorm(vp, 2 * n);
}
