BPOLY
#define gf_mulx(x) ((((x) & gf_c2) << 1) ^ ((((x) & gf_c1) >> 7) * BPOLY))
{ uint8_t p1 = x, p2 = BPOLY, n1 = hibit(x), n2 = 0x80, v1 = 1, v2 = 0;