/* mpn_toom_eval_dgr3_pm2 -- Evaluate a degree 3 polynomial in +2 and -2

   Contributed to the GNU project by Niels Möller

   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 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"

/* Needs n+1 limbs of temporary storage. */
int
mpn_toom_eval_dgr3_pm2 (mp_ptr xp2, mp_ptr xm2,
			mp_srcptr xp, mp_size_t n, mp_size_t x3n, mp_ptr tp)
{
  mp_limb_t cy;
  int neg;

  ASSERT (x3n > 0);
  ASSERT (x3n <= n);

  /* (x0 + 4 * x2) +/- (2 x1 + 8 x_3) */
#if HAVE_NATIVE_mpn_addlsh_n || HAVE_NATIVE_mpn_addlsh2_n
#if HAVE_NATIVE_mpn_addlsh2_n
  xp2[n] = mpn_addlsh2_n (xp2, xp, xp + 2*n, n);

  cy = mpn_addlsh2_n (tp, xp + n, xp + 3*n, x3n);
#else /* HAVE_NATIVE_mpn_addlsh_n */
  xp2[n] = mpn_addlsh_n (xp2, xp, xp + 2*n, n, 2);

  cy = mpn_addlsh_n (tp, xp + n, xp + 3*n, x3n, 2);
#endif
  if (x3n < n)
    cy = mpn_add_1 (tp + x3n, xp + n + x3n, n - x3n, cy);
  tp[n] = cy;
#else
  cy = mpn_lshift (tp, xp + 2*n, n, 2);
  xp2[n] = cy + mpn_add_n (xp2, tp, xp, n);

  tp[x3n] = mpn_lshift (tp, xp + 3*n, x3n, 2);
  if (x3n < n)
    tp[n] = mpn_add (tp, xp + n, n, tp, x3n + 1);
  else
    tp[n] += mpn_add_n (tp, xp + n, tp, n);
#endif
  mpn_lshift (tp, tp, n+1, 1);

  neg = (mpn_cmp (xp2, tp, n + 1) < 0) ? ~0 : 0;

#if HAVE_NATIVE_mpn_add_n_sub_n
  if (neg)
    mpn_add_n_sub_n (xp2, xm2, tp, xp2, n + 1);
  else
    mpn_add_n_sub_n (xp2, xm2, xp2, tp, n + 1);
#else
  if (neg)
    mpn_sub_n (xm2, tp, xp2, n + 1);
  else
    mpn_sub_n (xm2, xp2, tp, n + 1);

  mpn_add_n (xp2, xp2, tp, n + 1);
#endif

  ASSERT (xp2[n] < 15);
  ASSERT (xm2[n] < 10);

  return neg;
}
