/* -*-apcalc-*-
 *
 * Testbed for %$\gf{2}$% poltnomial arithmetic
 *
 * (c) 2000 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of Catacomb.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * Catacomb is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with Catacomb; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Object types ------------------------------------------------------*/

obj gf { x };

/*----- Static variables --------------------------------------------------*/

static obj gf example_gf_object;

/*----- Main code ---------------------------------------------------------*/

dummy = config("lib_debug", -1);

define gf(x)
{
  local obj gf g;
  g.x = x;
  return (g);
}

define gfint(x)
{
  if (istype(x, example_gf_object))
    return (x.x);
  else
    return (x);
}

define gf_add(x, y) = gf(xor(gfint(x), gfint(y)));
define gf_sub(x, y) = gf(xor(gfint(x), gfint(y)));
define gf_neg(x) = x;

define gf_mul(x, y)
{
  local a = gfint(x), b = gfint(y), z = 0, i, bits = highbit(a);
  for (i = 0; i <= bits; i++) {
    if (bit(a, i))
      z = xor(z, b << i);
  }
  return gf(z);
}

define gfx_div(rx, dx)
{
  local r = gfint(rx), d = gfint(dx), i;
  local q = 0, dbits, rbits;
  dbits = highbit(d);
  rbits = highbit(r);
  for (i = rbits - dbits; i >= 0; i--) {
    if (bit(r, i + dbits)) {
      r = xor(r, d << i);
      q |= (1 << i);
    }
  }
  return list(q, r);
}

define gf_div(x, y)
{
  local l;
  l = gfx_div(x, y);
  return gf(l[[0]]);
}

define gf_mod(x, y)
{
  local l;
  l = gfx_div(x, y);
  return gf(l[[1]]);
}

define gf_gcd(a, b)
{
  local swap = 0;
  local g, x = 1, X = 0, y = 0, Y = 1, q, r, t;
  if (a.x < b.x) {
    t = a; a = b; b = t;
    swap = 1;
  }
  if (b == gf(0))
    g = a;
  else {
    while (b != gf(0)) {
      q = gf_div(a, b); r = gf_mod(a, b);
      t = X * q + x; x = X; X = t;
      t = Y * q + y; y = Y; Y = t;
      a = b; b = r;
    }
    g = a;
  }
  if (swap) {
    t = x; x = y; y = t;
  }
  return list(g, x, y);
}

define gf_inv(a, b)
{
  local l = gf_gcd(b, a);
  if (l[[0]] != gf(1)) quit "not coprime in gf_inv";
  return l[[2]];
}

/*----- That's all, folks -------------------------------------------------*/