/* mpih-mul3.c  -  MPI helper functions
 * Copyright (C) 1994, 1996, 1997, 1998, 2001,
 *               2002 Free Software Foundation, Inc.
 *
 * This file is part of Libgcrypt.
 *
 * Libgcrypt is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * Libgcrypt 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser 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.
 */

#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include "mpi-internal.h"
#include "longlong.h"


mpi_limb_t
_gcry_mpih_submul_1( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
		  mpi_size_t s1_size, mpi_limb_t s2_limb)
{
  mpi_limb_t cy_limb;
  mpi_size_t j;
  mpi_limb_t prod_high, prod_low;
  mpi_limb_t x;

  /* The loop counter and index J goes from -SIZE to -1.  This way
   * the loop becomes faster.  */
  j = -s1_size;
  res_ptr -= j;
  s1_ptr -= j;

  cy_limb = 0;
  do 
    {
      umul_ppmm( prod_high, prod_low, s1_ptr[j], s2_limb);

      prod_low += cy_limb;
      cy_limb = (prod_low < cy_limb?1:0) + prod_high;

      x = res_ptr[j];
      prod_low = x - prod_low;
      cy_limb += prod_low > x?1:0;
      res_ptr[j] = prod_low;
    } 
  while( ++j );

  return cy_limb;
}