inv_mcol
# define inv_mcol im_sub
# define inv_mcol(x) four_tables(x,t_use(i,m),vf1,rf1,0)
# define inv_mcol(x) one_table(x,upr,t_use(i,m),vf1,rf1,0)
# define inv_mcol(x) (g2 = gf_mulx(x), g4 = gf_mulx(g2), g9 = (x) ^ gf_mulx(g4), g4 ^= g9, \