/* mpn_rshift -- Shift right low level.

Copyright 1991, 1993, 1994, 1996, 2000-2002 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 either:

  * the GNU Lesser General Public License as published by the Free

    Software Foundation; either version 3 of the License, or (at your

    option) any later version.

or

  * 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.

or both in parallel, as here.

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 General Public License

for more details.

You should have received copies of the GNU General Public License and the

GNU Lesser General Public License along with the GNU MP Library.  If not,

see https://www.gnu.org/licenses/.  */

#include "gmp.h"

#include "gmp-impl.h"

/* Shift U (pointed to by up and N limbs long) cnt bits to the right

   and store the n least significant limbs of the result at rp.

   The bits shifted out to the right are returned.

   Argument constraints:

   1. 0 < cnt < GMP_NUMB_BITS.

   2. If the result is to be written over the input, rp must be <= up.

*/

mp_limb_t

mpn_rshift (mp_ptr rp, mp_srcptr up, mp_size_t n, unsigned int cnt)

{

  mp_limb_t high_limb, low_limb;

  unsigned int tnc;

  mp_size_t i;

  mp_limb_t retval;

  ASSERT (n >= 1);

  ASSERT (cnt >= 1);

  ASSERT (cnt < GMP_NUMB_BITS);

  ASSERT (MPN_SAME_OR_INCR_P (rp, up, n));

  tnc = GMP_NUMB_BITS - cnt;

  high_limb = *up++;

  retval = (high_limb << tnc) & GMP_NUMB_MASK;

  low_limb = high_limb >> cnt;

  for (i = n - 1; i != 0; i--)

    {

      high_limb = *up++;

      *rp++ = low_limb | ((high_limb << tnc) & GMP_NUMB_MASK);

      low_limb = high_limb >> cnt;

    }

  *rp = low_limb;

  return retval;

}