/* Helper function for high degree Toom-Cook algorithms.

   Contributed to the GNU project by Marco Bodrato.

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

Copyright 2009, 2010 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"

/* Gets {pp,n} and (sign?-1:1)*{np,n}. Computes at once:
     {pp,n} <- ({pp,n}+{np,n})/2^{ps+1}
     {pn,n} <- ({pp,n}-{np,n})/2^{ns+1}
   Finally recompose them obtaining:
     {pp,n+off} <- {pp,n}+{np,n}*2^{off*GMP_NUMB_BITS}
*/
void
mpn_toom_couple_handling (mp_ptr pp, mp_size_t n, mp_ptr np,
			  int nsign, mp_size_t off, int ps, int ns)
{
  if (nsign) {
#ifdef HAVE_NATIVE_mpn_rsh1sub_n
    mpn_rsh1sub_n (np, pp, np, n);
#else
    mpn_sub_n (np, pp, np, n);
    mpn_rshift (np, np, n, 1);
#endif
  } else {
#ifdef HAVE_NATIVE_mpn_rsh1add_n
    mpn_rsh1add_n (np, pp, np, n);
#else
    mpn_add_n (np, pp, np, n);
    mpn_rshift (np, np, n, 1);
#endif
  }

#ifdef HAVE_NATIVE_mpn_rsh1sub_n
  if (ps == 1)
    mpn_rsh1sub_n (pp, pp, np, n);
  else
#endif
  {
    mpn_sub_n (pp, pp, np, n);
    if (ps > 0)
      mpn_rshift (pp, pp, n, ps);
  }
  if (ns > 0)
    mpn_rshift (np, np, n, ns);
  pp[n] = mpn_add_n (pp+off, pp+off, np, n-off);
  ASSERT_NOCARRY (mpn_add_1(pp+n, np+n-off, off, pp[n]) );
}
