/* mpn_toom_eval_pm2 -- Evaluate a polynomial in +2 and -2

   Contributed to the GNU project by Niels Möller and 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 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 either:

  * 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.

or

  * the GNU General Public License as published by the Free Software

    Foundation; either version 2 of the License, or (at your option) any

    later version.

or both in parallel, as here.

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 General Public License

for more details.

You should have received copies of the GNU General Public License and the

GNU Lesser General Public License along with the GNU MP Library.  If not,

see https://www.gnu.org/licenses/.  */

#include "gmp-impl.h"

/* DO_addlsh2(d,a,b,n,cy) computes cy,{d,n} <- {a,n} + 4*(cy,{b,n}), it

   can be used as DO_addlsh2(d,a,d,n,d[n]), for accumulation on {d,n+1}. */

#if HAVE_NATIVE_mpn_addlsh2_n

#define DO_addlsh2(d, a, b, n, cy)  \

do {         \

  (cy) <<= 2;       \

  (cy) += mpn_addlsh2_n(d, a, b, n); \

} while (0)

#else

#if HAVE_NATIVE_mpn_addlsh_n

#define DO_addlsh2(d, a, b, n, cy)  \

do {          \

  (cy) <<= 2;       \

  (cy) += mpn_addlsh_n(d, a, b, n, 2);  \

} while (0)

#else

/* The following is not a general substitute for addlsh2.

   It is correct if d == b, but it is not if d == a.  */

#define DO_addlsh2(d, a, b, n, cy)  \

do {          \

  (cy) <<= 2;       \

  (cy) += mpn_lshift(d, b, n, 2); \

  (cy) += mpn_add_n(d, d, a, n);  \

} while (0)

#endif

#endif

/* Evaluates a polynomial of degree 2 < k < GMP_NUMB_BITS, in the

   points +2 and -2. */

/* It returns 0 or ~0, depending on the sign of the result xm2. */

unsigned

mpn_toom_eval_pm2 (mp_ptr xp2, mp_ptr xm2, unsigned k,

       mp_srcptr xp, mp_size_t n, mp_size_t hn, mp_ptr tp)

{

  int i;

  unsigned neg;

  mp_limb_t cy;

  ASSERT (k >= 3);

  ASSERT (k < GMP_NUMB_BITS);

  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. */

  cy = 0;

  DO_addlsh2 (xp2, xp + (k-2) * n, xp + k * n, hn, cy);

  if (hn != n)

    cy = mpn_add_1 (xp2 + hn, xp + (k-2) * n + hn, n - hn, cy);

  for (i = k - 4; i >= 0; i -= 2)

    DO_addlsh2 (xp2, xp + i * n, xp2, n, cy);

  xp2[n] = cy;

  k--;

  cy = 0;

  DO_addlsh2 (tp, xp + (k-2) * n, xp + k * n, n, cy);

  for (i = k - 4; i >= 0; i -= 2)

    DO_addlsh2 (tp, xp + i * n, tp, n, cy);

  tp[n] = cy;

  if (k & 1)

    ASSERT_NOCARRY(mpn_lshift (tp , tp , n + 1, 1));

  else

    ASSERT_NOCARRY(mpn_lshift (xp2, xp2, n + 1, 1));

  neg = (mpn_cmp (xp2, tp, n + 1) < 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 /* !HAVE_NATIVE_mpn_add_n_sub_n */

  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 /* !HAVE_NATIVE_mpn_add_n_sub_n */

  ASSERT (xp2[n] < (1<<(k+2))-1);

  ASSERT (xm2[n] < ((1<<(k+3))-1 - (1^k&1))/3);

  neg ^= 1 ^ k & 1;

  return - neg;

}

#undef DO_addlsh2