`field_type_ff'
---------------

field_type_ff()
     :: $B@_Dj$5$l$F$$$k4pACBN$N<oN`(B

RETURN
     $B@0?t(B

   * $B@_Dj$5$l$F$$$k4pACBN$N<oN`$rJV$9(B.

   * $B@_Dj$J$7$J$i(B 0, GF(p) $B$J$i(B 1, GF(2^n) $B$J$i(B 2 $B$rJV$9(B.

     [0] field_type_ff();
     0
     [1] setmod_ff(3);
     3
     [2] field_type_ff();
     1
     [3] setmod_ff(x^2+x+1);
     x^2+x+1
     [4] field_type_ff();
     2

$B;2>H(B
     *Note `setmod_ff': setmod_ff

