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

   1 /* -*-c-*-
   2  *
   3  * $Id: exp.c,v 1.2 2004/04/08 01:36:15 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 /*----- Header files ------------------------------------------------------*/
  31
  32 #define EXP_TYPE /* Hack */
  33 #include "exp.h"
  34
  35 /*----- Main code ---------------------------------------------------------*/
  36
  37 /* --- @exp_simulnext@ --- *
  38  *
  39  * Arguments:   @exp_simul *e@ = pointer to state structure
  40  *              @size_t x@ = a current accumulator
  41  *
  42  * Returns:     The next column of bits.
  43  *
  44  * Use:         Scans the next column of bits for a simultaneous
  45  *              exponentiation.
  46  */
  47
  48 size_t exp_simulnext(exp_simul *e, size_t x)
  49 {
  50   size_t i;
  51
  52   /* --- Move to the next word along --- */
  53
  54   if (!e->b) {
  55     e->o--;
  56     for (i = 0; i < e->n; i++)
  57       e->s[i].w = e->o < e->s[i].len ? e->s[i].v[e->o] : 0;
  58     e->b = MPW_BITS;
  59   }
  60
  61   /* --- Scan out a column of bits --- */
  62
  63   for (i = 0; i < e->n; i++) {
  64     x = (x << 1) | ((e->s[i].w >> (MPW_BITS - 1)) & 1u);
  65     e->s[i].w <<= 1;
  66   }
  67   e->b--;
  68   return (x);
  69 }
  70
  71 /*----- That's all, folks -------------------------------------------------*/