gfmul
v = gfmul(v, 2);
v = gfmul(v, a);
a = gfmul(a, a);
printf("0x%02x,%c", gfmul(i, j + k),
printf("0x%02x,%c", gfmul(i, j + k),
printf("0x%02x,%c", gfmul(i, (j + k) << 4),