/* -*-apcalc-*-
*
- * $Id: gfx.cal,v 1.1 2000/10/08 16:01:37 mdw Exp $
+ * $Id: gfx.cal,v 1.3 2004/04/08 01:36:15 mdw Exp $
*
* Testbed for %$\gf{2}$% poltnomial arithmetic
*
* MA 02111-1307, USA.
*/
-/*----- Revision history --------------------------------------------------*
- *
- * $Log: gfx.cal,v $
- * Revision 1.1 2000/10/08 16:01:37 mdw
- * Prototypes of various bits of code.
- *
- */
-
/*----- Object types ------------------------------------------------------*/
obj gf { x };
define gfx_div(rx, dx)
{
local r = gfint(rx), d = gfint(dx), i;
- local q = 0, dbits = highbit(d), rbits = highbit(r);
+ 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);
define gf_div(x, y)
{
- local l = gfx_div(x, y);
+ local l;
+ l = gfx_div(x, y);
return gf(l[[0]]);
}
define gf_mod(x, y)
{
- local l = gfx_div(x, y);
+ local l;
+ l = gfx_div(x, y);
return gf(l[[1]]);
}
+define gf_inv(a, b)
+{
+ local g, x, y, X, Y, u, v, t, q, r;
+ x = gf(1); X = gf(0);
+ y = gf(0); Y = gf(1);
+
+ if (b == gf(0)) { g = a; } else if (a == gf(0)) { g = b; }
+ else {
+ while (b != gf(0)) {
+ q = gf_div(b, a); r = gf_mod(b, a);
+ t = X * q + x; x = X; X = t;
+ t = Y * q + y; y = Y; Y = t;
+ b = a; a = r;
+ }
+ g = a;
+ }
+ if (g != gf(1)) quit "not coprime in gf_inv";
+ return Y;
+}
+
/*----- That's all, folks -------------------------------------------------*/