LXR linux/lib/mpi/generic

   1/* mpihelp-mul_3.c  -  MPI helper functions
   2 * Copyright (C) 1994, 1996, 1997, 1998, 2001 Free Software Foundation, Inc.
   3 *
   4 * This file is part of GnuPG.
   5 *
   6 * GnuPG is free software; you can redistribute it and/or modify
   7 * it under the terms of the GNU General Public License as published by
   8 * the Free Software Foundation; either version 2 of the License, or
   9 * (at your option) any later version.
  10 *
  11 * GnuPG is distributed in the hope that it will be useful,
  12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 * GNU General Public License for more details.
  15 *
  16 * You should have received a copy of the GNU General Public License
  17 * along with this program; if not, write to the Free Software
  18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  19 *
  20 * Note: This code is heavily based on the GNU MP Library.
  21 *       Actually it's the same code with only minor changes in the
  22 *       way the data is stored; this is to support the abstraction
  23 *       of an optional secure memory allocation which may be used
  24 *       to avoid revealing of sensitive data due to paging etc.
  25 *       The GNU MP Library itself is published under the LGPL;
  26 *       however I decided to publish this code under the plain GPL.
  27 */
  28
  29#include "mpi-internal.h"
  30#include "longlong.h"
  31
  32mpi_limb_t
  33mpihelp_submul_1(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
  34                 mpi_size_t s1_size, mpi_limb_t s2_limb)
  35{
  36        mpi_limb_t cy_limb;
  37        mpi_size_t j;
  38        mpi_limb_t prod_high, prod_low;
  39        mpi_limb_t x;
  40
  41        /* The loop counter and index J goes from -SIZE to -1.  This way
  42         * the loop becomes faster.  */
  43        j = -s1_size;
  44        res_ptr -= j;
  45        s1_ptr -= j;
  46
  47        cy_limb = 0;
  48        do {
  49                umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
  50
  51                prod_low += cy_limb;
  52                cy_limb = (prod_low < cy_limb ? 1 : 0) + prod_high;
  53
  54                x = res_ptr[j];
  55                prod_low = x - prod_low;
  56                cy_limb += prod_low > x ? 1 : 0;
  57                res_ptr[j] = prod_low;
  58        } while (++j);
  59
  60        return cy_limb;
  61}
  62