/* mpz_fdiv_r_2exp -- Divide a integer by 2**CNT and produce a remainder.

Copyright (C) 1991, 1993, 1994, 1995, 1998, 1999 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 Library General Public License as published by
the Free Software Foundation; either version 2 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 Library General Public
License for more details.

You should have received a copy of the GNU Library 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 "gmp.h"
#include "gmp-impl.h"

void
#if __STDC__
mpz_fdiv_r_2exp (mpz_ptr res, mpz_srcptr in, unsigned long int cnt)
#else
mpz_fdiv_r_2exp (res, in, cnt)
     mpz_ptr res;
     mpz_srcptr in;
     unsigned long int cnt;
#endif
{
  mp_size_t in_size = ABS (in->_mp_size);
  mp_size_t res_size;
  mp_size_t limb_cnt = cnt / BITS_PER_MP_LIMB;
  mp_srcptr in_ptr = in->_mp_d;

  if (in_size > limb_cnt)
    {
      /* The input operand is (probably) greater than 2**CNT.  */
      mp_limb_t x;

      x = in_ptr[limb_cnt] & (((mp_limb_t) 1 << cnt % BITS_PER_MP_LIMB) - 1);
      if (x != 0)
	{
	  res_size = limb_cnt + 1;
	  if (res->_mp_alloc < res_size)
	    _mpz_realloc (res, res_size);

	  res->_mp_d[limb_cnt] = x;
	}
      else
	{
	  res_size = limb_cnt;
	  MPN_NORMALIZE (in_ptr, res_size);

	  if (res->_mp_alloc < res_size)
	    _mpz_realloc (res, res_size);

	  limb_cnt = res_size;
	}
    }
  else
    {
      /* The input operand is smaller than 2**CNT.  We perform a no-op,
	 apart from that we might need to copy IN to RES, and may need
	 to round the result.  */
      res_size = in_size;
      if (res->_mp_alloc < res_size)
	_mpz_realloc (res, res_size);

      limb_cnt = res_size;
    }

  if (res != in)
    MPN_COPY (res->_mp_d, in->_mp_d, limb_cnt);
  in_size = in->_mp_size;
  res->_mp_size = res_size;
  if (in_size < 0 && res_size != 0)
    {
      /* Result should be 2^CNT - RES */
      mpz_t tmp;
      MPZ_TMP_INIT (tmp, cnt/BITS_PER_MP_LIMB + 2);
      mpz_set_ui (tmp, 1L);
      mpz_mul_2exp (tmp, tmp, cnt);
      mpz_sub (res, tmp, res);
    }
}

/* This is an alternative ending of the above function using just low-level
   functions.  Tested, but perhaps excessive?  */
#if 0
  if (in->_mp_size < 0 && res_size != 0)
    {
      /* Result should be 2^CNT - RES */

      mp_ptr rp;

      limb_cnt = cnt / BITS_PER_MP_LIMB;

      if (res->_mp_alloc <= limb_cnt)
	_mpz_realloc (res, limb_cnt + 1);
      rp = PTR(res);
      if (res_size > limb_cnt)
	{
	  mpn_nz_neg (rp, rp, res_size);
	  rp[limb_cnt] &= ~(~(mp_limb_t) 0 << cnt % BITS_PER_MP_LIMB);
	  MPN_NORMALIZE_NOT_ZERO (rp, res_size);
	}
      else
	{
	  mp_size_t i;
	  mpn_nz_neg (rp, rp, res_size);
	  for (i = res_size; i < limb_cnt; i++)
	    rp[i] = ~ (mp_limb_t) 0;
	  res_size = limb_cnt;
	  if (cnt % BITS_PER_MP_LIMB != 0)
	    {
	      rp[res_size] = ((mp_limb_t) 1 << (cnt % BITS_PER_MP_LIMB)) - 1;
	      res_size++;
	    }
	  else
	    MPN_NORMALIZE_NOT_ZERO (rp, res_size);
	}
    }
  SIZ(res) = res_size;
}

static void
mpn_nz_neg (rp, sp, n)
     mp_ptr rp, sp;
     mp_size_t n;
{
  mp_size_t i;
  mp_limb_t x;

  x = sp[0];
  rp[0] = -x;
  for (i = 1; x == 0; i++)
    {
      x = sp[i];
      rp[i] = -x;
    }

  for (; i < n; i++)
    {
      rp[i] = ~sp[i];
    }
}
#endif
