grub-core/lib/libgcrypt-grub/mpi/mpih-mul3.c

   1 /* mpih-mul3.c  -  MPI helper functions
   2  * Copyright (C) 1994, 1996, 1997, 1998, 2001,
   3  *               2002 Free Software Foundation, Inc.
   4  *
   5  * This file is part of Libgcrypt.
   6  *
   7  * Libgcrypt is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU Lesser General Public License as
   9  * published by the Free Software Foundation; either version 2.1 of
  10  * the License, or (at your option) any later version.
  11  *
  12  * Libgcrypt 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 Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License 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  */
  27
  28 #include <config.h>
  29 #include <stdio.h>
  30 #include <stdlib.h>
  31 #include "mpi-internal.h"
  32 #include "longlong.h"
  33
  34
  35 mpi_limb_t
  36 _gcry_mpih_submul_1( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
  37                   mpi_size_t s1_size, mpi_limb_t s2_limb)
  38 {
  39   mpi_limb_t cy_limb;
  40   mpi_size_t j;
  41   mpi_limb_t prod_high, prod_low;
  42   mpi_limb_t x;
  43
  44   /* The loop counter and index J goes from -SIZE to -1.  This way
  45    * the loop becomes faster.  */
  46   j = -s1_size;
  47   res_ptr -= j;
  48   s1_ptr -= j;
  49
  50   cy_limb = 0;
  51   do
  52     {
  53       umul_ppmm( prod_high, prod_low, s1_ptr[j], s2_limb);
  54
  55       prod_low += cy_limb;
  56       cy_limb = (prod_low < cy_limb?1:0) + prod_high;
  57
  58       x = res_ptr[j];
  59       prod_low = x - prod_low;
  60       cy_limb += prod_low > x?1:0;
  61       res_ptr[j] = prod_low;
  62     }
  63   while( ++j );
  64
  65   return cy_limb;
  66 }
  67
  68