lib/mpi/mpih-cmp.c

   1 /* mpihelp-sub.c  -  MPI helper functions
   2  *      Copyright (C) 1994, 1996 Free Software Foundation, Inc.
   3  *      Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
   4  *
   5  * This file is part of GnuPG.
   6  *
   7  * GnuPG is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * GnuPG is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  20  *
  21  * Note: This code is heavily based on the GNU MP Library.
  22  *       Actually it's the same code with only minor changes in the
  23  *       way the data is stored; this is to support the abstraction
  24  *       of an optional secure memory allocation which may be used
  25  *       to avoid revealing of sensitive data due to paging etc.
  26  *       The GNU MP Library itself is published under the LGPL;
  27  *       however I decided to publish this code under the plain GPL.
  28  */
  29
  30 #include "mpi-internal.h"
  31
  32 /****************
  33  * Compare OP1_PTR/OP1_SIZE with OP2_PTR/OP2_SIZE.
  34  * There are no restrictions on the relative sizes of
  35  * the two arguments.
  36  * Return 1 if OP1 > OP2, 0 if they are equal, and -1 if OP1 < OP2.
  37  */
  38 int mpihelp_cmp(mpi_ptr_t op1_ptr, mpi_ptr_t op2_ptr, mpi_size_t size)
  39 {
  40         mpi_size_t i;
  41         mpi_limb_t op1_word, op2_word;
  42
  43         for (i = size - 1; i >= 0; i--) {
  44                 op1_word = op1_ptr[i];
  45                 op2_word = op2_ptr[i];
  46                 if (op1_word != op2_word)
  47                         goto diff;
  48         }
  49         return 0;
  50
  51 diff:
  52         /* This can *not* be simplified to
  53          *   op2_word - op2_word
  54          * since that expression might give signed overflow.  */
  55         return (op1_word > op2_word) ? 1 : -1;
  56 }