static void cmov(ref GroupElementPreComp t, ref GroupElementPreComp u, byte b)
{
FieldOperations.fe_cmov(ref t.yplusx, ref u.yplusx, b);
FieldOperations.fe_cmov(ref t.yminusx, ref u.yminusx, b);
FieldOperations.fe_cmov(ref t.xy2d, ref u.xy2d, b);
}