source/libs/gmp/gmp-src/mpz/powm_sec.c

   1 /* mpz_powm_sec(res,base,exp,mod) -- Set R to (U^E) mod M.
   2
   3    Contributed to the GNU project by Torbjorn Granlund.
   4
   5 Copyright 1991, 1993, 1994, 1996, 1997, 2000-2002, 2005, 2008, 2009, 2012 Free
   6 Software Foundation, Inc.
   7
   8 This file is part of the GNU MP Library.
   9
  10 The GNU MP Library is free software; you can redistribute it and/or modify
  11 it under the terms of either:
  12
  13   * the GNU Lesser General Public License as published by the Free
  14     Software Foundation; either version 3 of the License, or (at your
  15     option) any later version.
  16
  17 or
  18
  19   * the GNU General Public License as published by the Free Software
  20     Foundation; either version 2 of the License, or (at your option) any
  21     later version.
  22
  23 or both in parallel, as here.
  24
  25 The GNU MP Library is distributed in the hope that it will be useful, but
  26 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  27 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  28 for more details.
  29
  30 You should have received copies of the GNU General Public License and the
  31 GNU Lesser General Public License along with the GNU MP Library.  If not,
  32 see https://www.gnu.org/licenses/.  */
  33
  34
  35 #include "gmp.h"
  36 #include "gmp-impl.h"
  37
  38
  39 void
  40 mpz_powm_sec (mpz_ptr r, mpz_srcptr b, mpz_srcptr e, mpz_srcptr m)
  41 {
  42   mp_size_t n;
  43   mp_ptr rp, tp;
  44   mp_srcptr bp, ep, mp;
  45   mp_size_t rn, bn, es, en;
  46   TMP_DECL;
  47
  48   n = ABSIZ(m);
  49
  50   mp = PTR(m);
  51
  52   if (UNLIKELY ((n == 0) || (mp[0] % 2 == 0)))
  53     DIVIDE_BY_ZERO;
  54
  55   es = SIZ(e);
  56   if (UNLIKELY (es <= 0))
  57     {
  58       if (es == 0)
  59         {
  60           /* b^0 mod m,  b is anything and m is non-zero.
  61              Result is 1 mod m, i.e., 1 or 0 depending on if m = 1.  */
  62           SIZ(r) = n != 1 || mp[0] != 1;
  63           PTR(r)[0] = 1;
  64           return;
  65         }
  66       DIVIDE_BY_ZERO;
  67     }
  68   en = es;
  69
  70   bn = ABSIZ(b);
  71
  72   if (UNLIKELY (bn == 0))
  73     {
  74       SIZ(r) = 0;
  75       return;
  76     }
  77
  78   TMP_MARK;
  79   tp = TMP_ALLOC_LIMBS (n + mpn_sec_powm_itch (bn, en * GMP_NUMB_BITS, n));
  80
  81   rp = tp;  tp += n;
  82
  83   bp = PTR(b);
  84   ep = PTR(e);
  85
  86   mpn_sec_powm (rp, bp, bn, ep, en * GMP_NUMB_BITS, mp, n, tp);
  87
  88   rn = n;
  89
  90   MPN_NORMALIZE (rp, rn);
  91
  92   if ((ep[0] & 1) && SIZ(b) < 0 && rn != 0)
  93     {
  94       mpn_sub (rp, PTR(m), n, rp, rn);
  95       rn = n;
  96       MPN_NORMALIZE (rp, rn);
  97     }
  98
  99   MPZ_REALLOC (r, rn);
 100   SIZ(r) = rn;
 101   MPN_COPY (PTR(r), rp, rn);
 102
 103   TMP_FREE;
 104 }