/* Set b=b mod c */
public void mod(FF c)
{
int k = 0;
norm();
if (comp(this, c) < 0)
{
return;
}
do
{
c.shl();
k++;
} while (comp(this, c) >= 0);
while (k > 0)
{
c.shr();
if (comp(this, c) >= 0)
{
sub(c);
norm();
}
k--;
}
}