/* mpn_udiv_w_sdiv -- implement udiv_qrnnd on machines with only signed
   division.

   Contributed by Peter L. Montgomery.

   THIS IS AN INTERNAL FUNCTION WITH A MUTABLE INTERFACE.  IT IS ONLY SAFE
   TO REACH THIS FUNCTION THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS
   ALMOST GUARANTEED THAT THIS FUNCTION WILL CHANGE OR DISAPPEAR IN A FUTURE
   GNU MP RELEASE.


Copyright 1992, 1994, 1996, 2000 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 3 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.  If not, see http://www.gnu.org/licenses/.  */

#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"

mp_limb_t
mpn_udiv_w_sdiv (rp, a1, a0, d)
     mp_limb_t *rp, a1, a0, d;
{
  mp_limb_t q, r;
  mp_limb_t c0, c1, b1;

  ASSERT (d != 0);
  ASSERT (a1 < d);

  if ((mp_limb_signed_t) d >= 0)
    {
      if (a1 < d - a1 - (a0 >> (BITS_PER_MP_LIMB - 1)))
	{
	  /* dividend, divisor, and quotient are nonnegative */
	  sdiv_qrnnd (q, r, a1, a0, d);
	}
      else
	{
	  /* Compute c1*2^32 + c0 = a1*2^32 + a0 - 2^31*d */
	  sub_ddmmss (c1, c0, a1, a0, d >> 1, d << (BITS_PER_MP_LIMB - 1));
	  /* Divide (c1*2^32 + c0) by d */
	  sdiv_qrnnd (q, r, c1, c0, d);
	  /* Add 2^31 to quotient */
	  q += (mp_limb_t) 1 << (BITS_PER_MP_LIMB - 1);
	}
    }
  else
    {
      b1 = d >> 1;			/* d/2, between 2^30 and 2^31 - 1 */
      c1 = a1 >> 1;			/* A/2 */
      c0 = (a1 << (BITS_PER_MP_LIMB - 1)) + (a0 >> 1);

      if (a1 < b1)			/* A < 2^32*b1, so A/2 < 2^31*b1 */
	{
	  sdiv_qrnnd (q, r, c1, c0, b1); /* (A/2) / (d/2) */

	  r = 2*r + (a0 & 1);		/* Remainder from A/(2*b1) */
	  if ((d & 1) != 0)
	    {
	      if (r >= q)
		r = r - q;
	      else if (q - r <= d)
		{
		  r = r - q + d;
		  q--;
		}
	      else
		{
		  r = r - q + 2*d;
		  q -= 2;
		}
	    }
	}
      else if (c1 < b1)			/* So 2^31 <= (A/2)/b1 < 2^32 */
	{
	  c1 = (b1 - 1) - c1;
	  c0 = ~c0;			/* logical NOT */

	  sdiv_qrnnd (q, r, c1, c0, b1); /* (A/2) / (d/2) */

	  q = ~q;			/* (A/2)/b1 */
	  r = (b1 - 1) - r;

	  r = 2*r + (a0 & 1);		/* A/(2*b1) */

	  if ((d & 1) != 0)
	    {
	      if (r >= q)
		r = r - q;
	      else if (q - r <= d)
		{
		  r = r - q + d;
		  q--;
		}
	      else
		{
		  r = r - q + 2*d;
		  q -= 2;
		}
	    }
	}
      else				/* Implies c1 = b1 */
	{				/* Hence a1 = d - 1 = 2*b1 - 1 */
	  if (a0 >= -d)
	    {
	      q = -1;
	      r = a0 + d;
	    }
	  else
	    {
	      q = -2;
	      r = a0 + 2*d;
	    }
	}
    }

  *rp = r;
  return q;
}
