/* Read x bit and then reset it */
negative = bignum_bit(point->y, point->curve->fieldBits - 1);
bignum_set_bit(point->y, point->curve->fieldBits - 1, 0);
+ bn_restore_invariant(point->y);
/* Get the x from the y */
point->x = ecp_edx(point->curve, point->y);