1  /* mpn_toom_eval_pm1 -- Evaluate a polynomial in +1 and -1
       2  
       3     Contributed to the GNU project by Niels Möller
       4  
       5     THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE.  IT IS ONLY
       6     SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS ALMOST
       7     GUARANTEED THAT IT WILL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
       8  
       9  Copyright 2009 Free Software Foundation, Inc.
      10  
      11  This file is part of the GNU MP Library.
      12  
      13  The GNU MP Library is free software; you can redistribute it and/or modify
      14  it under the terms of either:
      15  
      16    * the GNU Lesser General Public License as published by the Free
      17      Software Foundation; either version 3 of the License, or (at your
      18      option) any later version.
      19  
      20  or
      21  
      22    * the GNU General Public License as published by the Free Software
      23      Foundation; either version 2 of the License, or (at your option) any
      24      later version.
      25  
      26  or both in parallel, as here.
      27  
      28  The GNU MP Library is distributed in the hope that it will be useful, but
      29  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
      30  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
      31  for more details.
      32  
      33  You should have received copies of the GNU General Public License and the
      34  GNU Lesser General Public License along with the GNU MP Library.  If not,
      35  see https://www.gnu.org/licenses/.  */
      36  
      37  
      38  #include "gmp-impl.h"
      39  
      40  /* Evaluates a polynomial of degree k > 3, in the points +1 and -1. */
      41  int
      42  mpn_toom_eval_pm1 (mp_ptr xp1, mp_ptr xm1, unsigned k,
      43  		   mp_srcptr xp, mp_size_t n, mp_size_t hn, mp_ptr tp)
      44  {
      45    unsigned i;
      46    int neg;
      47  
      48    ASSERT (k >= 4);
      49  
      50    ASSERT (hn > 0);
      51    ASSERT (hn <= n);
      52  
      53    /* The degree k is also the number of full-size coefficients, so
      54     * that last coefficient, of size hn, starts at xp + k*n. */
      55  
      56    xp1[n] = mpn_add_n (xp1, xp, xp + 2*n, n);
      57    for (i = 4; i < k; i += 2)
      58      ASSERT_NOCARRY (mpn_add (xp1, xp1, n+1, xp+i*n, n));
      59  
      60    tp[n] = mpn_add_n (tp, xp + n, xp + 3*n, n);
      61    for (i = 5; i < k; i += 2)
      62      ASSERT_NOCARRY (mpn_add (tp, tp, n+1, xp+i*n, n));
      63  
      64    if (k & 1)
      65      ASSERT_NOCARRY (mpn_add (tp, tp, n+1, xp+k*n, hn));
      66    else
      67      ASSERT_NOCARRY (mpn_add (xp1, xp1, n+1, xp+k*n, hn));
      68  
      69    neg = (mpn_cmp (xp1, tp, n + 1) < 0) ? ~0 : 0;
      70  
      71  #if HAVE_NATIVE_mpn_add_n_sub_n
      72    if (neg)
      73      mpn_add_n_sub_n (xp1, xm1, tp, xp1, n + 1);
      74    else
      75      mpn_add_n_sub_n (xp1, xm1, xp1, tp, n + 1);
      76  #else
      77    if (neg)
      78      mpn_sub_n (xm1, tp, xp1, n + 1);
      79    else
      80      mpn_sub_n (xm1, xp1, tp, n + 1);
      81  
      82    mpn_add_n (xp1, xp1, tp, n + 1);
      83  #endif
      84  
      85    ASSERT (xp1[n] <= k);
      86    ASSERT (xm1[n] <= k/2 + 1);
      87  
      88    return neg;
      89  }