aes.c

openswan

    r(23,e8,e8,cb), r(7c,dd,dd,a1), r(9c,74,74,e8), r(21,1f,1f,3e),\
    r(dd,4b,4b,96), r(dc,bd,bd,61), r(86,8b,8b,0d), r(85,8a,8a,0f),\
    r(90,70,70,e0), r(42,3e,3e,7c), r(c4,b5,b5,71), r(aa,66,66,cc),\
    r(d8,48,48,90), r(05,03,03,06), r(01,f6,f6,f7), r(12,0e,0e,1c),\
    r(a3,61,61,c2), r(5f,35,35,6a), r(f9,57,57,ae), r(d0,b9,b9,69),\
    r(91,86,86,17), r(58,c1,c1,99), r(27,1d,1d,3a), r(b9,9e,9e,27),\
    r(38,e1,e1,d9), r(13,f8,f8,eb), r(b3,98,98,2b), r(33,11,11,22),\
    r(bb,69,69,d2), r(70,d9,d9,a9), r(89,8e,8e,07), r(a7,94,94,33),\
    r(b6,9b,9b,2d), r(22,1e,1e,3c), r(92,87,87,15), r(20,e9,e9,c9),\
    r(49,ce,ce,87), r(ff,55,55,aa), r(78,28,28,50), r(7a,df,df,a5),\
    r(8f,8c,8c,03), r(f8,a1,a1,59), r(80,89,89,09), r(17,0d,0d,1a),\
    r(da,bf,bf,65), r(31,e6,e6,d7), r(c6,42,42,84), r(b8,68,68,d0),\
    r(c3,41,41,82), r(b0,99,99,29), r(77,2d,2d,5a), r(11,0f,0f,1e),\
    r(cb,b0,b0,7b), r(fc,54,54,a8), r(d6,bb,bb,6d), r(3a,16,16,2c)

//  data for inverse tables (other than last round)

#define i_table \
    r(50,a7,f4,51), r(53,65,41,7e), r(c3,a4,17,1a), r(96,5e,27,3a),\
    r(cb,6b,ab,3b), r(f1,45,9d,1f), r(ab,58,fa,ac), r(93,03,e3,4b),\
    r(55,fa,30,20), r(f6,6d,76,ad), r(91,76,cc,88), r(25,4c,02,f5),\
    r(fc,d7,e5,4f), r(d7,cb,2a,c5), r(80,44,35,26), r(8f,a3,62,b5),\
    r(49,5a,b1,de), r(67,1b,ba,25), r(98,0e,ea,45), r(e1,c0,fe,5d),\
    r(02,75,2f,c3), r(12,f0,4c,81), r(a3,97,46,8d), r(c6,f9,d3,6b),\
    r(e7,5f,8f,03), r(95,9c,92,15), r(eb,7a,6d,bf), r(da,59,52,95),\
    r(2d,83,be,d4), r(d3,21,74,58), r(29,69,e0,49), r(44,c8,c9,8e),\
    r(6a,89,c2,75), r(78,79,8e,f4), r(6b,3e,58,99), r(dd,71,b9,27),\
    r(b6,4f,e1,be), r(17,ad,88,f0), r(66,ac,20,c9), r(b4,3a,ce,7d),\
    r(18,4a,df,63), r(82,31,1a,e5), r(60,33,51,97), r(45,7f,53,62),\
    r(e0,77,64,b1), r(84,ae,6b,bb), r(1c,a0,81,fe), r(94,2b,08,f9),\
    r(58,68,48,70), r(19,fd,45,8f), r(87,6c,de,94), r(b7,f8,7b,52),\
    r(23,d3,73,ab), r(e2,02,4b,72), r(57,8f,1f,e3), r(2a,ab,55,66),\
    r(07,28,eb,b2), r(03,c2,b5,2f), r(9a,7b,c5,86), r(a5,08,37,d3),\
    r(f2,87,28,30), r(b2,a5,bf,23), r(ba,6a,03,02), r(5c,82,16,ed),\
    r(2b,1c,cf,8a), r(92,b4,79,a7), r(f0,f2,07,f3), r(a1,e2,69,4e),\
    r(cd,f4,da,65), r(d5,be,05,06), r(1f,62,34,d1), r(8a,fe,a6,c4),\
    r(9d,53,2e,34), r(a0,55,f3,a2), r(32,e1,8a,05), r(75,eb,f6,a4),\
    r(39,ec,83,0b), r(aa,ef,60,40), r(06,9f,71,5e), r(51,10,6e,bd),\
    r(f9,8a,21,3e), r(3d,06,dd,96), r(ae,05,3e,dd), r(46,bd,e6,4d),\
    r(b5,8d,54,91), r(05,5d,c4,71), r(6f,d4,06,04), r(ff,15,50,60),\
    r(24,fb,98,19), r(97,e9,bd,d6), r(cc,43,40,89), r(77,9e,d9,67),\
    r(bd,42,e8,b0), r(88,8b,89,07), r(38,5b,19,e7), r(db,ee,c8,79),\
    r(47,0a,7c,a1), r(e9,0f,42,7c), r(c9,1e,84,f8), r(00,00,00,00),\
    r(83,86,80,09), r(48,ed,2b,32), r(ac,70,11,1e), r(4e,72,5a,6c),\
    r(fb,ff,0e,fd), r(56,38,85,0f), r(1e,d5,ae,3d), r(27,39,2d,36),\
    r(64,d9,0f,0a), r(21,a6,5c,68), r(d1,54,5b,9b), r(3a,2e,36,24),\
    r(b1,67,0a,0c), r(0f,e7,57,93), r(d2,96,ee,b4), r(9e,91,9b,1b),\
    r(4f,c5,c0,80), r(a2,20,dc,61), r(69,4b,77,5a), r(16,1a,12,1c),\
    r(0a,ba,93,e2), r(e5,2a,a0,c0), r(43,e0,22,3c), r(1d,17,1b,12),\
    r(0b,0d,09,0e), r(ad,c7,8b,f2), r(b9,a8,b6,2d), r(c8,a9,1e,14),\
    r(85,19,f1,57), r(4c,07,75,af), r(bb,dd,99,ee), r(fd,60,7f,a3),\
    r(9f,26,01,f7), r(bc,f5,72,5c), r(c5,3b,66,44), r(34,7e,fb,5b),\
    r(76,29,43,8b), r(dc,c6,23,cb), r(68,fc,ed,b6), r(63,f1,e4,b8),\
    r(ca,dc,31,d7), r(10,85,63,42), r(40,22,97,13), r(20,11,c6,84),\
    r(7d,24,4a,85), r(f8,3d,bb,d2), r(11,32,f9,ae), r(6d,a1,29,c7),\
    r(4b,2f,9e,1d), r(f3,30,b2,dc), r(ec,52,86,0d), r(d0,e3,c1,77),\
    r(6c,16,b3,2b), r(99,b9,70,a9), r(fa,48,94,11), r(22,64,e9,47),\
    r(c4,8c,fc,a8), r(1a,3f,f0,a0), r(d8,2c,7d,56), r(ef,90,33,22),\
    r(c7,4e,49,87), r(c1,d1,38,d9), r(fe,a2,ca,8c), r(36,0b,d4,98),\
    r(cf,81,f5,a6), r(28,de,7a,a5), r(26,8e,b7,da), r(a4,bf,ad,3f),\
    r(e4,9d,3a,2c), r(0d,92,78,50), r(9b,cc,5f,6a), r(62,46,7e,54),\
    r(c2,13,8d,f6), r(e8,b8,d8,90), r(5e,f7,39,2e), r(f5,af,c3,82),\
    r(be,80,5d,9f), r(7c,93,d0,69), r(a9,2d,d5,6f), r(b3,12,25,cf),\
    r(3b,99,ac,c8), r(a7,7d,18,10), r(6e,63,9c,e8), r(7b,bb,3b,db),\
    r(09,78,26,cd), r(f4,18,59,6e), r(01,b7,9a,ec), r(a8,9a,4f,83),\
    r(65,6e,95,e6), r(7e,e6,ff,aa), r(08,cf,bc,21), r(e6,e8,15,ef),\
    r(d9,9b,e7,ba), r(ce,36,6f,4a), r(d4,09,9f,ea), r(d6,7c,b0,29),\
    r(af,b2,a4,31), r(31,23,3f,2a), r(30,94,a5,c6), r(c0,66,a2,35),\
    r(37,bc,4e,74), r(a6,ca,82,fc), r(b0,d0,90,e0), r(15,d8,a7,33),\
    r(4a,98,04,f1), r(f7,da,ec,41), r(0e,50,cd,7f), r(2f,f6,91,17),\
    r(8d,d6,4d,76), r(4d,b0,ef,43), r(54,4d,aa,cc), r(df,04,96,e4),\
    r(e3,b5,d1,9e), r(1b,88,6a,4c), r(b8,1f,2c,c1), r(7f,51,65,46),\
    r(04,ea,5e,9d), r(5d,35,8c,01), r(73,74,87,fa), r(2e,41,0b,fb),\
    r(5a,1d,67,b3), r(52,d2,db,92), r(33,56,10,e9), r(13,47,d6,6d),\
    r(8c,61,d7,9a), r(7a,0c,a1,37), r(8e,14,f8,59), r(89,3c,13,eb),\
    r(ee,27,a9,ce), r(35,c9,61,b7), r(ed,e5,1c,e1), r(3c,b1,47,7a),\
    r(59,df,d2,9c), r(3f,73,f2,55), r(79,ce,14,18), r(bf,37,c7,73),\
    r(ea,cd,f7,53), r(5b,aa,fd,5f), r(14,6f,3d,df), r(86,db,44,78),\
    r(81,f3,af,ca), r(3e,c4,68,b9), r(2c,34,24,38), r(5f,40,a3,c2),\
    r(72,c3,1d,16), r(0c,25,e2,bc), r(8b,49,3c,28), r(41,95,0d,ff),\
    r(71,01,a8,39), r(de,b3,0c,08), r(9c,e4,b4,d8), r(90,c1,56,64),\
    r(61,84,cb,7b), r(70,b6,32,d5), r(74,5c,6c,48), r(42,57,b8,d0)

// generate the required tables in the desired endian format

#undef  r
#define r   r0

#if defined(ONE_TABLE)
static const u_int32_t ft_tab[256] =
    {   f_table };
#elif defined(FOUR_TABLES)
static const u_int32_t ft_tab[4][256] =
{   {   f_table },
#undef  r
#define r   r1
    {   f_table },
#undef  r
#define r   r2
    {   f_table },
#undef  r
#define r   r3
    {   f_table }
};
#endif

#undef  r
#define r   r0
#if defined(ONE_TABLE)
static const u_int32_t it_tab[256] =
    {   i_table };
#elif defined(FOUR_TABLES)
static const u_int32_t it_tab[4][256] =
{   {   i_table },
#undef  r
#define r   r1
    {   i_table },
#undef  r
#define r   r2
    {   i_table },
#undef  r
#define r   r3
    {   i_table }
};
#endif

#endif

#if defined(FIXED_TABLES) && (defined(ONE_LR_TABLE) || defined(FOUR_LR_TABLES)) 

//  data for inverse tables (last round)

#define li_table    \
    w(52), w(09), w(6a), w(d5), w(30), w(36), w(a5), w(38),\
    w(bf), w(40), w(a3), w(9e), w(81), w(f3), w(d7), w(fb),\
    w(7c), w(e3), w(39), w(82), w(9b), w(2f), w(ff), w(87),\
    w(34), w(8e), w(43), w(44), w(c4), w(de), w(e9), w(cb),\
    w(54), w(7b), w(94), w(32), w(a6), w(c2), w(23), w(3d),\
    w(ee), w(4c), w(95), w(0b), w(42), w(fa), w(c3), w(4e),\
    w(08), w(2e), w(a1), w(66), w(28), w(d9), w(24), w(b2),\
    w(76), w(5b), w(a2), w(49), w(6d), w(8b), w(d1), w(25),\
    w(72), w(f8), w(f6), w(64), w(86), w(68), w(98), w(16),\
    w(d4), w(a4), w(5c), w(cc), w(5d), w(65), w(b6), w(92),\
    w(6c), w(70), w(48), w(50), w(fd), w(ed), w(b9), w(da),\
    w(5e), w(15), w(46), w(57), w(a7), w(8d), w(9d), w(84),\
    w(90), w(d8), w(ab), w(00), w(8c), w(bc), w(d3), w(0a),\
    w(f7), w(e4), w(58), w(05), w(b8), w(b3), w(45), w(06),\
    w(d0), w(2c), w(1e), w(8f), w(ca), w(3f), w(0f), w(02),\
    w(c1), w(af), w(bd), w(03), w(01), w(13), w(8a), w(6b),\
    w(3a), w(91), w(11), w(41), w(4f), w(67), w(dc), w(ea),\
    w(97), w(f2), w(cf), w(ce), w(f0), w(b4), w(e6), w(73),\
    w(96), w(ac), w(74), w(22), w(e7), w(ad), w(35), w(85),\
    w(e2), w(f9), w(37), w(e8), w(1c), w(75), w(df), w(6e),\
    w(47), w(f1), w(1a), w(71), w(1d), w(29), w(c5), w(89),\
    w(6f), w(b7), w(62), w(0e), w(aa), w(18), w(be), w(1b),\
    w(fc), w(56), w(3e), w(4b), w(c6), w(d2), w(79), w(20),\
    w(9a), w(db), w(c0), w(fe), w(78), w(cd), w(5a), w(f4),\
    w(1f), w(dd), w(a8), w(33), w(88), w(07), w(c7), w(31),\
    w(b1), w(12), w(10), w(59), w(27), w(80), w(ec), w(5f),\
    w(60), w(51), w(7f), w(a9), w(19), w(b5), w(4a), w(0d),\
    w(2d), w(e5), w(7a), w(9f), w(93), w(c9), w(9c), w(ef),\
    w(a0), w(e0), w(3b), w(4d), w(ae), w(2a), w(f5), w(b0),\
    w(c8), w(eb), w(bb), w(3c), w(83), w(53), w(99), w(61),\
    w(17), w(2b), w(04), w(7e), w(ba), w(77), w(d6), w(26),\
    w(e1), w(69), w(14), w(63), w(55), w(21), w(0c), w(7d),

// generate the required tables in the desired endian format

#undef  r
#define r(p,q,r,s)  w0(q)
#if defined(ONE_LR_TABLE)
static const u_int32_t fl_tab[256] =
    {   f_table     };
#elif defined(FOUR_LR_TABLES)
static const u_int32_t fl_tab[4][256] =
{   {   f_table    },
#undef  r
#define r(p,q,r,s)   w1(q)
    {   f_table    },
#undef  r
#define r(p,q,r,s)   w2(q)
    {   f_table    },
#undef  r
#define r(p,q,r,s)   w3(q)
    {   f_table    }
};
#endif

#undef  w
#define w   w0
#if defined(ONE_LR_TABLE)
static const u_int32_t il_tab[256] =
    {   li_table    };
#elif defined(FOUR_LR_TABLES)
static const u_int32_t il_tab[4][256] =
{   {   li_table    },
#undef  w
#define w   w1
    {   li_table    },
#undef  w
#define w   w2
    {   li_table    },
#undef  w
#define w   w3
    {   li_table    }
};
#endif

#endif

#if defined(FIXED_TABLES) && (defined(ONE_IM_TABLE) || defined(FOUR_IM_TABLES)) 

#define m_table \
    r(00,00,00,00), r(0b,0d,09,0e), r(16,1a,12,1c), r(1d,17,1b,12),\
    r(2c,34,24,38), r(27,39,2d,36), r(3a,2e,36,24), r(31,23,3f,2a),\
    r(58,68,48,70), r(53,65,41,7e), r(4e,72,5a,6c), r(45,7f,53,62),\
    r(74,5c,6c,48), r(7f,51,65,46), r(62,46,7e,54), r(69,4b,77,5a),\
    r(b0,d0,90,e0), r(bb,dd,99,ee), r(a6,ca,82,fc), r(ad,c7,8b,f2),\
    r(9c,e4,b4,d8), r(97,e9,bd,d6), r(8a,fe,a6,c4), r(81,f3,af,ca),\
    r(e8,b8,d8,90), r(e3,b5,d1,9e), r(fe,a2,ca,8c), r(f5,af,c3,82),\
    r(c4,8c,fc,a8), r(cf,81,f5,a6), r(d2,96,ee,b4), r(d9,9b,e7,ba),\
    r(7b,bb,3b,db), r(70,b6,32,d5), r(6d,a1,29,c7), r(66,ac,20,c9),\
    r(57,8f,1f,e3), r(5c,82,16,ed), r(41,95,0d,ff), r(4a,98,04,f1),\
    r(23,d3,73,ab), r(28,de,7a,a5), r(35,c9,61,b7), r(3e,c4,68,b9),\
    r(0f,e7,57,93), r(04,ea,5e,9d), r(19,fd,45,8f), r(12,f0,4c,81),\
    r(cb,6b,ab,3b), r(c0,66,a2,35), r(dd,71,b9,27), r(d6,7c,b0,29),\
    r(e7,5f,8f,03), r(ec,52,86,0d), r(f1,45,9d,1f), r(fa,48,94,11),\
    r(93,03,e3,4b), r(98,0e,ea,45), r(85,19,f1,57), r(8e,14,f8,59),\
    r(bf,37,c7,73), r(b4,3a,ce,7d), r(a9,2d,d5,6f), r(a2,20,dc,61),\
    r(f6,6d,76,ad), r(fd,60,7f,a3), r(e0,77,64,b1), r(eb,7a,6d,bf),\
    r(da,59,52,95), r(d1,54,5b,9b), r(cc,43,40,89), r(c7,4e,49,87),\
    r(ae,05,3e,dd), r(a5,08,37,d3), r(b8,1f,2c,c1), r(b3,12,25,cf),\
    r(82,31,1a,e5), r(89,3c,13,eb), r(94,2b,08,f9), r(9f,26,01,f7),\
    r(46,bd,e6,4d), r(4d,b0,ef,43), r(50,a7,f4,51), r(5b,aa,fd,5f),\
    r(6a,89,c2,75), r(61,84,cb,7b), r(7c,93,d0,69), r(77,9e,d9,67),\
    r(1e,d5,ae,3d), r(15,d8,a7,33), r(08,cf,bc,21), r(03,c2,b5,2f),\
    r(32,e1,8a,05), r(39,ec,83,0b), r(24,fb,98,19), r(2f,f6,91,17),\
    r(8d,d6,4d,76), r(86,db,44,78), r(9b,cc,5f,6a), r(90,c1,56,64),\
    r(a1,e2,69,4e), r(aa,ef,60,40), r(b7,f8,7b,52), r(bc,f5,72,5c),\
    r(d5,be,05,06), r(de,b3,0c,08), r(c3,a4,17,1a), r(c8,a9,1e,14),\
    r(f9,8a,21,3e), r(f2,87,28,30), r(ef,90,33,22), r(e4,9d,3a,2c),\
    r(3d,06,dd,96), r(36,0b,d4,98), r(2b,1c,cf,8a), r(20,11,c6,84),\
    r(11,32,f9,ae), r(1a,3f,f0,a0), r(07,28,eb,b2), r(0c,25,e2,bc),\
    r(65,6e,95,e6), r(6e,63,9c,e8), r(73,74,87,fa), r(78,79,8e,f4),\
    r(49,5a,b1,de), r(42,57,b8,d0), r(5f,40,a3,c2), r(54,4d,aa,cc),\
    r(f7,da,ec,41), r(fc,d7,e5,4f), r(e1,c0,fe,5d), r(ea,cd,f7,53),\
    r(db,ee,c8,79), r(d0,e3,c1,77), r(cd,f4,da,65), r(c6,f9,d3,6b),\
    r(af,b2,a4,31), r(a4,bf,ad,3f), r(b9,a8,b6,2d), r(b2,a5,bf,23),\
    r(83,86,80,09), r(88,8b,89,07), r(95,9c,92,15), r(9e,91,9b,1b),\
    r(47,0a,7c,a1), r(4c,07,75,af), r(51,10,6e,bd), r(5a,1d,67,b3),\
    r(6b,3e,58,99), r(60,33,51,97), r(7d,24,4a,85), r(76,29,43,8b),\
    r(1f,62,34,d1), r(14,6f,3d,df), r(09,78,26,cd), r(02,75,2f,c3),\
    r(33,56,10,e9), r(38,5b,19,e7), r(25,4c,02,f5), r(2e,41,0b,fb),\
    r(8c,61,d7,9a), r(87,6c,de,94), r(9a,7b,c5,86), r(91,76,cc,88),\
    r(a0,55,f3,a2), r(ab,58,fa,ac), r(b6,4f,e1,be), r(bd,42,e8,b0),\
    r(d4,09,9f,ea), r(df,04,96,e4), r(c2,13,8d,f6), r(c9,1e,84,f8),\
    r(f8,3d,bb,d2), r(f3,30,b2,dc), r(ee,27,a9,ce), r(e5,2a,a0,c0),\
    r(3c,b1,47,7a), r(37,bc,4e,74), r(2a,ab,55,66), r(21,a6,5c,68),\
    r(10,85,63,42), r(1b,88,6a,4c), r(06,9f,71,5e), r(0d,92,78,50),\
    r(64,d9,0f,0a), r(6f,d4,06,04), r(72,c3,1d,16), r(79,ce,14,18),\
    r(48,ed,2b,32), r(43,e0,22,3c), r(5e,f7,39,2e), r(55,fa,30,20),\
    r(01,b7,9a,ec), r(0a,ba,93,e2), r(17,ad,88,f0), r(1c,a0,81,fe),\
    r(2d,83,be,d4), r(26,8e,b7,da), r(3b,99,ac,c8), r(30,94,a5,c6),\
    r(59,df,d2,9c), r(52,d2,db,92), r(4f,c5,c0,80), r(44,c8,c9,8e),\
    r(75,eb,f6,a4), r(7e,e6,ff,aa), r(63,f1,e4,b8), r(68,fc,ed,b6),\
    r(b1,67,0a,0c), r(ba,6a,03,02), r(a7,7d,18,10), r(ac,70,11,1e),\
    r(9d,53,2e,34), r(96,5e,27,3a), r(8b,49,3c,28), r(80,44,35,26),\
    r(e9,0f,42,7c), r(e2,02,4b,72), r(ff,15,50,60), r(f4,18,59,6e),\
    r(c5,3b,66,44), r(ce,36,6f,4a), r(d3,21,74,58), r(d8,2c,7d,56),\
    r(7a,0c,a1,37), r(71,01,a8,39), r(6c,16,b3,2b), r(67,1b,ba,25),\
    r(56,38,85,0f), r(5d,35,8c,01), r(40,22,97,13), r(4b,2f,9e,1d),\
    r(22,64,e9,47), r(29,69,e0,49), r(34,7e,fb,5b), r(3f,73,f2,55),\
    r(0e,50,cd,7f), r(05,5d,c4,71), r(18,4a,df,63), r(13,47,d6,6d),\
    r(ca,dc,31,d7), r(c1,d1,38,d9), r(dc,c6,23,cb), r(d7,cb,2a,c5),\
    r(e6,e8,15,ef), r(ed,e5,1c,e1), r(f0,f2,07,f3), r(fb,ff,0e,fd),\
    r(92,b4,79,a7), r(99,b9,70,a9), r(84,ae,6b,bb), r(8f,a3,62,b5),\
    r(be,80,5d,9f), r(b5,8d,54,91), r(a8,9a,4f,83), r(a3,97,46,8d)

#undef r
#define r   r0

#if defined(ONE_IM_TABLE)
static const u_int32_t im_tab[256] =
    {   m_table };
#elif defined(FOUR_IM_TABLES)
static const u_int32_t im_tab[4][256] =
{   {   m_table },
#undef  r
#define r   r1
    {   m_table },
#undef  r
#define r   r2
    {   m_table },
#undef  r
#define r   r3
    {   m_table }
};
#endif

#endif

#else

static int tab_gen = 0;

static unsigned char  s_box[256];            // the S box
static unsigned char  inv_s_box[256];        // the inverse S box
static u_int32_t  rcon_tab[AES_RC_LENGTH];   // table of round constants

#if defined(ONE_TABLE)
static u_int32_t  ft_tab[256];
static u_int32_t  it_tab[256];
#elif defined(FOUR_TABLES)
static u_int32_t  ft_tab[4][256];
static u_int32_t  it_tab[4][256];
#endif

#if defined(ONE_LR_TABLE)
static u_int32_t  fl_tab[256];
static u_int32_t  il_tab[256];
#elif defined(FOUR_LR_TABLES)
static u_int32_t  fl_tab[4][256];
static u_int32_t  il_tab[4][256];
#endif

#if defined(ONE_IM_TABLE)
static u_int32_t  im_tab[256];
#elif defined(FOUR_IM_TABLES)
static u_int32_t  im_tab[4][256];
#endif

// Generate the tables for the dynamic table option

#if !defined(FF_TABLES)

// It will generally be sensible to use tables to compute finite 
// field multiplies and inverses but where memory is scarse this 
// code might sometimes be better.

// return 2 ^ (n - 1) where n is the bit number of the highest bit
// set in x with x in the range 1 < x < 0x00000200.   This form is
// used so that locals within FFinv can be bytes rather than words

static unsigned char hibit(const u_int32_t x)
{   unsigned char r = (unsigned char)((x >> 1) | (x >> 2));
    
    r |= (r >> 2);
    r |= (r >> 4);
    return (r + 1) >> 1;
}

// return the inverse of the finite field element x

static unsigned char FFinv(const unsigned char x)