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

   1 /* -*-c-*-
   2  *
   3  * $Id: exp.c,v 1.1 2001/06/16 13:00:59 mdw Exp $
   4  *
   5  * Generalized exponentiation
   6  *
   7  * (c) 2001 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 /*----- Revision history --------------------------------------------------*
  31  *
  32  * $Log: exp.c,v $
  33  * Revision 1.1  2001/06/16 13:00:59  mdw
  34  * New generic exponentation code.  Includes sliding-window simultaneous
  35  * exponentiation.
  36  *
  37  */
  38
  39 /*----- Header files ------------------------------------------------------*/
  40
  41 #define EXP_TYPE /* Hack */
  42 #include "exp.h"
  43
  44 /*----- Main code ---------------------------------------------------------*/
  45
  46 /* --- @exp_simulnext@ --- *
  47  *
  48  * Arguments:   @exp_simul *e@ = pointer to state structure
  49  *              @size_t x@ = a current accumulator
  50  *
  51  * Returns:     The next column of bits.
  52  *
  53  * Use:         Scans the next column of bits for a simultaneous
  54  *              exponentiation.
  55  */
  56
  57 size_t exp_simulnext(exp_simul *e, size_t x)
  58 {
  59   size_t i;
  60
  61   /* --- Move to the next word along --- */
  62
  63   if (!e->b) {
  64     e->o--;
  65     for (i = 0; i < e->n; i++)
  66       e->s[i].w = e->o < e->s[i].len ? e->s[i].v[e->o] : 0;
  67     e->b = MPW_BITS;
  68   }
  69
  70   /* --- Scan out a column of bits --- */
  71
  72   for (i = 0; i < e->n; i++) {
  73     x = (x << 1) | ((e->s[i].w >> (MPW_BITS - 1)) & 1u);
  74     e->s[i].w <<= 1;
  75   }
  76   e->b--;
  77   return (x);
  78 }
  79
  80 /*----- That's all, folks -------------------------------------------------*/