fixmul
z = fixmul(x0, a[0]);
x0 = fixmul(x0, x);
z = fixmul(x0, a[i]) + z;
x = fixmul(x, FIX1E);
x = fixmul(x, FIXE);
z = fixmul(z, y);
x = fixmul(x, FIX1E);
x = fixmul(x, FIXE);