/* -*-c-*-
*
- * $Id: mpbarrett-exp.c,v 1.2 2004/04/08 01:36:15 mdw Exp $
+ * $Id$
*
* Modular exponentiation using Barrett reduction
*
* (c) 2004 Straylight/Edgeware
*/
-/*----- Licensing notice --------------------------------------------------*
+/*----- Licensing notice --------------------------------------------------*
*
* This file is part of Catacomb.
*
* 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,
/* --- @mpbarrett_exp@ --- *
*
* Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
- * @mp *d@ = fake destination
- * @mp *a@ = base
- * @mp *e@ = exponent
+ * @mp *d@ = fake destination
+ * @mp *a@ = base
+ * @mp *e@ = exponent
*
- * Returns: Result, %$a^e \bmod m$%.
+ * Returns: Result, %$a^e \bmod m$%.
*/
mp *mpbarrett_exp(mpbarrett *mb, mp *d, mp *a, mp *e)
MP_COPY(a);
MP_SHRINK(e);
- if (e->f & MP_NEG)
- a = mp_modinv(a, a, mb->m);
- if (!MP_LEN(e))
+ if (MP_ZEROP(e))
;
- else if (MP_LEN(e) < EXP_THRESH)
- EXP_SIMPLE(x, a, e);
- else
- EXP_WINDOW(x, a, e);
+ else {
+ if (MP_NEGP(e))
+ a = mp_modinv(a, a, mb->m);
+ if (MP_LEN(e) < EXP_THRESH)
+ EXP_SIMPLE(x, a, e);
+ else
+ EXP_WINDOW(x, a, e);
+ }
mp_drop(d);
mp_drop(spare);
mp_drop(a);