fixpoint_mul
fixpoint_mul(&tmp, &tmp, &tfrc_recv_w[i]);
fixpoint_mul(&tmp, &tmp, &tfrc_recv_w[i-1]);
fixpoint_mul(&x1, &x1, &y1); \
fixpoint_mul(&z, x, &y);
struct fixpoint *fixpoint_mul(struct fixpoint *, const struct fixpoint *,
fixpoint_mul(&v, &v, &w);
fixpoint_mul(&x, &x, &y);