/* mpn_toom_eval_pm1 -- Evaluate a polynomial in +1 and -1

   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"

/* Evaluates a polynomial of degree k > 3, in the points +1 and -1. */
int
mpn_toom_eval_pm1 (mp_ptr xp1, mp_ptr xm1, unsigned k,
		   mp_srcptr xp, mp_size_t n, mp_size_t hn, mp_ptr tp)
{
  unsigned i;
  int neg;

  ASSERT (k >= 4);

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

  /* The degree k is also the number of full-size coefficients, so
   * that last coefficient, of size hn, starts at xp + k*n. */

  xp1[n] = mpn_add_n (xp1, xp, xp + 2*n, n);
  for (i = 4; i < k; i += 2)
    ASSERT_NOCARRY (mpn_add (xp1, xp1, n+1, xp+i*n, n));

  tp[n] = mpn_add_n (tp, xp + n, xp + 3*n, n);
  for (i = 5; i < k; i += 2)
    ASSERT_NOCARRY (mpn_add (tp, tp, n+1, xp+i*n, n));

  if (k & 1)
    ASSERT_NOCARRY (mpn_add (tp, tp, n+1, xp+k*n, hn));
  else
    ASSERT_NOCARRY (mpn_add (xp1, xp1, n+1, xp+k*n, hn));

  neg = (mpn_cmp (xp1, tp, n + 1) < 0) ? ~0 : 0;

#if HAVE_NATIVE_mpn_add_n_sub_n
  if (neg)
    mpn_add_n_sub_n (xp1, xm1, tp, xp1, n + 1);
  else
    mpn_add_n_sub_n (xp1, xm1, xp1, tp, n + 1);
#else
  if (neg)
    mpn_sub_n (xm1, tp, xp1, n + 1);
  else
    mpn_sub_n (xm1, xp1, tp, n + 1);

  mpn_add_n (xp1, xp1, tp, n + 1);
#endif

  ASSERT (xp1[n] <= k);
  ASSERT (xm1[n] <= k/2 + 1);

  return neg;
}