1  /* mpn_toom_eval_dgr3_pm2 -- Evaluate a degree 3 polynomial in +2 and -2
       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  /* Needs n+1 limbs of temporary storage. */
      41  int
      42  mpn_toom_eval_dgr3_pm2 (mp_ptr xp2, mp_ptr xm2,
      43  			mp_srcptr xp, mp_size_t n, mp_size_t x3n, mp_ptr tp)
      44  {
      45    mp_limb_t cy;
      46    int neg;
      47  
      48    ASSERT (x3n > 0);
      49    ASSERT (x3n <= n);
      50  
      51    /* (x0 + 4 * x2) +/- (2 x1 + 8 x_3) */
      52  #if HAVE_NATIVE_mpn_addlsh_n || HAVE_NATIVE_mpn_addlsh2_n
      53  #if HAVE_NATIVE_mpn_addlsh2_n
      54    xp2[n] = mpn_addlsh2_n (xp2, xp, xp + 2*n, n);
      55  
      56    cy = mpn_addlsh2_n (tp, xp + n, xp + 3*n, x3n);
      57  #else /* HAVE_NATIVE_mpn_addlsh_n */
      58    xp2[n] = mpn_addlsh_n (xp2, xp, xp + 2*n, n, 2);
      59  
      60    cy = mpn_addlsh_n (tp, xp + n, xp + 3*n, x3n, 2);
      61  #endif
      62    if (x3n < n)
      63      cy = mpn_add_1 (tp + x3n, xp + n + x3n, n - x3n, cy);
      64    tp[n] = cy;
      65  #else
      66    cy = mpn_lshift (tp, xp + 2*n, n, 2);
      67    xp2[n] = cy + mpn_add_n (xp2, tp, xp, n);
      68  
      69    tp[x3n] = mpn_lshift (tp, xp + 3*n, x3n, 2);
      70    if (x3n < n)
      71      tp[n] = mpn_add (tp, xp + n, n, tp, x3n + 1);
      72    else
      73      tp[n] += mpn_add_n (tp, xp + n, tp, n);
      74  #endif
      75    mpn_lshift (tp, tp, n+1, 1);
      76  
      77    neg = (mpn_cmp (xp2, tp, n + 1) < 0) ? ~0 : 0;
      78  
      79  #if HAVE_NATIVE_mpn_add_n_sub_n
      80    if (neg)
      81      mpn_add_n_sub_n (xp2, xm2, tp, xp2, n + 1);
      82    else
      83      mpn_add_n_sub_n (xp2, xm2, xp2, tp, n + 1);
      84  #else
      85    if (neg)
      86      mpn_sub_n (xm2, tp, xp2, n + 1);
      87    else
      88      mpn_sub_n (xm2, xp2, tp, n + 1);
      89  
      90    mpn_add_n (xp2, xp2, tp, n + 1);
      91  #endif
      92  
      93    ASSERT (xp2[n] < 15);
      94    ASSERT (xm2[n] < 10);
      95  
      96    return neg;
      97  }