mpih-cmp.c

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/* mpihelp-sub.c  -  MPI helper functions
 *  Copyright (C) 1994, 1996 Free Software Foundation, Inc.
 *  Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * GnuPG is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 *
 * Note: This code is heavily based on the GNU MP Library.
 *   Actually it's the same code with only minor changes in the
 *   way the data is stored; this is to support the abstraction
 *   of an optional secure memory allocation which may be used
 *   to avoid revealing of sensitive data due to paging etc.
 *   The GNU MP Library itself is published under the LGPL;
 *   however I decided to publish this code under the plain GPL.
 */

#include "mpi-internal.h"

/****************
 * Compare OP1_PTR/OP1_SIZE with OP2_PTR/OP2_SIZE.
 * There are no restrictions on the relative sizes of
 * the two arguments.
 * Return 1 if OP1 > OP2, 0 if they are equal, and -1 if OP1 < OP2.
 */
int mpihelp_cmp(mpi_ptr_t op1_ptr, mpi_ptr_t op2_ptr, mpi_size_t size)
{
    mpi_size_t i;
    mpi_limb_t op1_word, op2_word;

    for (i = size - 1; i >= 0; i--) {
        op1_word = op1_ptr[i];
        op2_word = op2_ptr[i];
        if (op1_word != op2_word)
            goto diff;
    }
    return 0;

diff:
    /* This can *not* be simplified to
     *   op2_word - op2_word
     * since that expression might give signed overflow.  */
    return (op1_word > op2_word) ? 1 : -1;
}