git.distorted.org.uk Git - u/mdw/catacomb/blob - mp-exp.c

   1 /* -*-c-*-
   2  *
   3  * $Id$
   4  *
   5  * Exponentiation for large integers
   6  *
   7  * (c) 2004 Straylight/Edgeware
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of Catacomb.
  13  *
  14  * Catacomb is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU Library General Public License as
  16  * published by the Free Software Foundation; either version 2 of the
  17  * License, or (at your option) any later version.
  18  *
  19  * Catacomb is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU Library General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU Library General Public
  25  * License along with Catacomb; if not, write to the Free
  26  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  27  * MA 02111-1307, USA.
  28  */
  29
  30 /*----- Header files ------------------------------------------------------*/
  31
  32 #include <assert.h>
  33
  34 #include "mp.h"
  35 #include "mp-exp.h"
  36
  37 /*----- Main code ---------------------------------------------------------*/
  38
  39 /* --- @mp_exp@ --- *
  40  *
  41  * Arguments:   @mp *d@ = fake destination
  42  *              @mp *a@ = base
  43  *              @mp *e@ = exponent
  44  *
  45  * Returns:     Result, %$a^e$%.
  46  */
  47
  48 mp *mp_exp(mp *d, mp *a, mp *e)
  49 {
  50   mp *x = MP_ONE;
  51   mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
  52   assert(!MP_NEGP(e));
  53
  54   MP_COPY(a);
  55   if (MP_ZEROP(e))
  56     ;
  57   else if (MP_LEN(e) < EXP_THRESH)
  58     EXP_SIMPLE(x, a, e);
  59   else
  60     EXP_WINDOW(x, a, e);
  61   mp_drop(d);
  62   mp_drop(spare);
  63   mp_drop(a);
  64   return (x);
  65 }
  66
  67 /*----- That's all, folks -------------------------------------------------*/