/* -*-c-*-
*
- * $Id: mp-gcd.c,v 1.6 2004/03/21 22:52:06 mdw Exp $
+ * $Id: mp-gcd.c,v 1.7 2004/04/08 01:36:15 mdw Exp $
*
* Extended GCD calculation
*
* MA 02111-1307, USA.
*/
-/*----- Revision history --------------------------------------------------*
- *
- * $Log: mp-gcd.c,v $
- * Revision 1.6 2004/03/21 22:52:06 mdw
- * Merge and close elliptic curve branch.
- *
- * Revision 1.5.4.1 2004/03/21 22:39:46 mdw
- * Elliptic curves on binary fields work.
- *
- * Revision 1.5 2000/10/08 12:02:41 mdw
- * Use Euclid's algorithm rather than the binary one.
- *
- * Revision 1.4 2000/06/17 11:34:46 mdw
- * More hacking for the signs of the outputs.
- *
- * Revision 1.3 1999/12/10 23:18:39 mdw
- * Change interface for suggested destinations.
- *
- * Revision 1.2 1999/11/22 20:49:56 mdw
- * Fix bug which failed to favour `x' when `y' wasn't wanted and the two
- * arguments needed swapping.
- *
- * Revision 1.1 1999/11/17 18:02:16 mdw
- * New multiprecision integer arithmetic suite.
- *
- */
-
/*----- Header files ------------------------------------------------------*/
#include "mp.h"
MP_DROP(a); MP_DROP(b);
}
+/* -- @mp_modinv@ --- *
+ *
+ * Arguments: @mp *d@ = destination
+ * @mp *x@ = argument
+ * @mp *p@ = modulus
+ *
+ * Returns: The inverse %$x^{-1} \bmod p$%.
+ *
+ * Use: Computes a modular inverse. An assertion fails if %$p$%
+ * has no inverse.
+ */
+
+mp *mp_modinv(mp *d, mp *x, mp *p)
+{
+ mp *g = MP_NEW;
+ mp_gcd(&g, 0, &d, p, x);
+ assert(MP_EQ(g, MP_ONE));
+ mp_drop(g);
+ return (d);
+}
+
/*----- Test rig ----------------------------------------------------------*/
#ifdef TEST_RIG