/* -*-c-*-
*
- * $Id: mpbarrett-exp.c,v 1.1 2004/04/01 12:50:09 mdw Exp $
+ * $Id: mpbarrett-exp.c,v 1.2 2004/04/08 01:36:15 mdw Exp $
*
* Modular exponentiation using Barrett reduction
*
* MA 02111-1307, USA.
*/
-/*----- Revision history --------------------------------------------------*
- *
- * $Log: mpbarrett-exp.c,v $
- * Revision 1.1 2004/04/01 12:50:09 mdw
- * Add cyclic group abstraction, with test code. Separate off exponentation
- * functions for better static linking. Fix a buttload of bugs on the way.
- * Generally ensure that negative exponents do inversion correctly. Add
- * table of standard prime-field subgroups. (Binary field subgroups are
- * currently unimplemented but easy to add if anyone ever finds a good one.)
- *
- */
-
/*----- Header files ------------------------------------------------------*/
#include "mp.h"
MP_COPY(a);
MP_SHRINK(e);
- if (e->f & MP_NEG) {
- mp *g = MP_NEW;
- mp_gcd(&g, 0, &a, mb->m, a);
- assert(MP_EQ(g, MP_ONE));
- mp_drop(g);
- }
+ if (e->f & MP_NEG)
+ a = mp_modinv(a, a, mb->m);
if (!MP_LEN(e))
;
else if (MP_LEN(e) < EXP_THRESH)