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

   1 /* -*-c-*-
   2  *
   3  * Modular exponentiation using Barrett reduction
   4  *
   5  * (c) 2004 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Catacomb.
  11  *
  12  * Catacomb is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * Catacomb is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with Catacomb; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 /*----- Header files ------------------------------------------------------*/
  29
  30 #include "mp.h"
  31 #include "mpbarrett.h"
  32 #include "mpbarrett-exp.h"
  33
  34 /*----- Main code ---------------------------------------------------------*/
  35
  36 /* --- @mpbarrett_exp@ --- *
  37  *
  38  * Arguments:   @mpbarrett *mb@ = pointer to Barrett reduction context
  39  *              @mp *d@ = fake destination
  40  *              @mp *a@ = base
  41  *              @mp *e@ = exponent
  42  *
  43  * Returns:     Result, %$a^e \bmod m$%.
  44  */
  45
  46 mp *mpbarrett_exp(mpbarrett *mb, mp *d, mp *a, mp *e)
  47 {
  48   mp *x = MP_ONE;
  49   mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
  50
  51   MP_COPY(a);
  52   MP_SHRINK(e);
  53   if (MP_ZEROP(e))
  54     ;
  55   else {
  56     if (MP_NEGP(e))
  57       a = mp_modinv(a, a, mb->m);
  58     if (MP_LEN(e) < EXP_THRESH)
  59       EXP_SIMPLE(x, a, e);
  60     else
  61       EXP_WINDOW(x, a, e);
  62   }
  63   mp_drop(d);
  64   mp_drop(spare);
  65   mp_drop(a);
  66   return (x);
  67 }
  68
  69 /*----- Test rig ----------------------------------------------------------*/
  70
  71 #ifdef TEST_RIG
  72
  73 static int vexp(dstr *v)
  74 {
  75   mp *m = *(mp **)v[0].buf;
  76   mp *a = *(mp **)v[1].buf;
  77   mp *b = *(mp **)v[2].buf;
  78   mp *r = *(mp **)v[3].buf;
  79   mp *mr;
  80   int ok = 1;
  81
  82   mpbarrett mb;
  83   mpbarrett_create(&mb, m);
  84
  85   mr = mpbarrett_exp(&mb, MP_NEW, a, b);
  86
  87   if (!MP_EQ(mr, r)) {
  88     fputs("\n*** barrett modexp failed", stderr);
  89     fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
  90     fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);
  91     fputs("\n e = ", stderr); mp_writefile(b, stderr, 10);
  92     fputs("\n r = ", stderr); mp_writefile(r, stderr, 10);
  93     fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10);
  94     fputc('\n', stderr);
  95     ok = 0;
  96   }
  97
  98   mp_drop(m);
  99   mp_drop(a);
 100   mp_drop(b);
 101   mp_drop(r);
 102   mp_drop(mr);
 103   mpbarrett_destroy(&mb);
 104   assert(mparena_count(MPARENA_GLOBAL) == 0);
 105   return ok;
 106 }
 107
 108 static test_chunk tests[] = {
 109   { "mpbarrett-exp", vexp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
 110   { 0, 0, { 0 } }
 111 };
 112
 113 int main(int argc, char *argv[])
 114 {
 115   sub_init();
 116   test_run(argc, argv, tests, SRCDIR "/t/mpbarrett");
 117   return (0);
 118 }
 119
 120 #endif
 121
 122 /*----- That's all, folks -------------------------------------------------*/