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/* mpn_rshift -- Shift right a low-level natural-number integer.

Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP Library 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.

The GNU MP Library 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 the GNU MP Library; see the file COPYING.LIB.  If not, write to

the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,

MA 02111-1307, USA. */

#include <config.h>

#include "gmp-impl.h"

/* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right

   and store the USIZE least significant limbs of the result at WP.

   The bits shifted out to the right are returned.

   Argument constraints:

   1. 0 < CNT < BITS_PER_MP_LIMB

   2. If the result is to be written over the input, WP must be <= UP.

*/

mp_limb_t

#if __STDC__

mpn_rshift (register mp_ptr wp,

            register mp_srcptr up, mp_size_t usize,

            register unsigned int cnt)

#else

mpn_rshift (wp, up, usize, cnt)

     register mp_ptr wp;

     register mp_srcptr up;

     mp_size_t usize;

     register unsigned int cnt;

#endif

{

  register mp_limb_t high_limb, low_limb;

  register unsigned sh_1, sh_2;

  register mp_size_t i;

  mp_limb_t retval;

#ifdef DEBUG

  if (usize == 0 || cnt == 0)

    abort ();

#endif

  sh_1 = cnt;

#if 0

  if (sh_1 == 0)

    {

      if (wp != up)

        {

          /* Copy from low end to high end, to allow specified input/output

             overlapping.  */

          for (i = 0; i < usize; i++)

            wp[i] = up[i];

        }

      return usize;

    }

#endif

  wp -= 1;

  sh_2 = BITS_PER_MP_LIMB - sh_1;

  high_limb = up[0];

  retval = high_limb << sh_2;

  low_limb = high_limb;

  for (i = 1; i < usize; i++)

    {

      high_limb = up[i];

      wp[i] = (low_limb >> sh_1) | (high_limb << sh_2);

      low_limb = high_limb;

    }

  wp[i] = low_limb >> sh_1;

  return retval;

}