/* -*-c-*-
*
- * $Id: gf-gcd.c,v 1.1.2.1 2004/03/21 22:39:46 mdw Exp $
+ * $Id: gf-gcd.c,v 1.3 2004/04/08 01:36:15 mdw Exp $
*
* Euclidian algorithm on binary polynomials
*
* MA 02111-1307, USA.
*/
-/*----- Revision history --------------------------------------------------*
- *
- * $Log: gf-gcd.c,v $
- * Revision 1.1.2.1 2004/03/21 22:39:46 mdw
- * Elliptic curves on binary fields work.
- *
- */
-
/*----- Header files ------------------------------------------------------*/
#include "gf.h"
MP_DROP(a); MP_DROP(b);
}
+/* -- @gf_modinv@ --- *
+ *
+ * Arguments: @mp *d@ = destination
+ * @mp *x@ = argument
+ * @mp *p@ = modulus
+ *
+ * Returns: The inverse %$x^{-1} \bmod p$%.
+ *
+ * Use: Computes a modular inverse, the catch being that the
+ * arguments and results are binary polynomials. An assertion
+ * fails if %$p$% has no inverse.
+ */
+
+mp *gf_modinv(mp *d, mp *x, mp *p)
+{
+ mp *g = MP_NEW;
+ gf_gcd(&g, 0, &d, p, x);
+ assert(MP_EQ(g, MP_ONE));
+ mp_drop(g);
+ return (d);
+}
+
/*----- Test rig ----------------------------------------------------------*/
#ifdef TEST_RIG
mp *gg = MP_NEW, *xx = MP_NEW, *yy = MP_NEW;
gf_gcd(&gg, &xx, &yy, a, b);
if (!MP_EQ(x, xx)) {
- fputs("\n*** mp_gcd(x) failed", stderr);
+ fputs("\n*** gf_gcd(x) failed", stderr);
fputs("\na = ", stderr); mp_writefile(a, stderr, 16);
fputs("\nb = ", stderr); mp_writefile(b, stderr, 16);
fputs("\nexpect = ", stderr); mp_writefile(x, stderr, 16);
ok = 0;
}
if (!MP_EQ(y, yy)) {
- fputs("\n*** mp_gcd(y) failed", stderr);
+ fputs("\n*** gf_gcd(y) failed", stderr);
fputs("\na = ", stderr); mp_writefile(a, stderr, 16);
fputs("\nb = ", stderr); mp_writefile(b, stderr, 16);
fputs("\nexpect = ", stderr); mp_writefile(y, stderr, 16);
}
if (!MP_EQ(g, gg)) {
- fputs("\n*** mp_gcd(gcd) failed", stderr);
+ fputs("\n*** gf_gcd(gcd) failed", stderr);
fputs("\na = ", stderr); mp_writefile(a, stderr, 16);
fputs("\nb = ", stderr); mp_writefile(b, stderr, 16);
fputs("\nexpect = ", stderr); mp_writefile(g, stderr, 16);