/* a=1/a mod 2^256. This is very fast! */
public virtual void invmod2m()
{
int i;
BIG U = new BIG(0);
BIG b = new BIG(0);
BIG c = new BIG(0);
U.inc(invmod256(lastbits(8)));
for (i = 8; i < 256; i <<= 1)
{
b.copy(this);
b.mod2m(i);
BIG t1 = BIG.smul(U, b);
t1.shr(i);
c.copy(this);
c.shr(i);
c.mod2m(i);
BIG t2 = BIG.smul(U, c);
t2.mod2m(i);
t1.add(t2);
b = BIG.smul(t1, U);
t1.copy(b);
t1.mod2m(i);
t2.one();
t2.shl(i);
t1.rsub(t2);
t1.norm();
t1.shl(i);
U.add(t1);
}
this.copy(U);
}
