source/libs/gmp/gmp-src/mpn/generic/toom_eval_dgr3_pm2.c

   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.h"
  39 #include "gmp-impl.h"
  40
  41 /* Needs n+1 limbs of temporary storage. */
  42 int
  43 mpn_toom_eval_dgr3_pm2 (mp_ptr xp2, mp_ptr xm2,
  44                         mp_srcptr xp, mp_size_t n, mp_size_t x3n, mp_ptr tp)
  45 {
  46   mp_limb_t cy;
  47   int neg;
  48
  49   ASSERT (x3n > 0);
  50   ASSERT (x3n <= n);
  51
  52   /* (x0 + 4 * x2) +/- (2 x1 + 8 x_3) */
  53 #if HAVE_NATIVE_mpn_addlsh_n || HAVE_NATIVE_mpn_addlsh2_n
  54 #if HAVE_NATIVE_mpn_addlsh2_n
  55   xp2[n] = mpn_addlsh2_n (xp2, xp, xp + 2*n, n);
  56
  57   cy = mpn_addlsh2_n (tp, xp + n, xp + 3*n, x3n);
  58 #else /* HAVE_NATIVE_mpn_addlsh_n */
  59   xp2[n] = mpn_addlsh_n (xp2, xp, xp + 2*n, n, 2);
  60
  61   cy = mpn_addlsh_n (tp, xp + n, xp + 3*n, x3n, 2);
  62 #endif
  63   if (x3n < n)
  64     cy = mpn_add_1 (tp + x3n, xp + n + x3n, n - x3n, cy);
  65   tp[n] = cy;
  66 #else
  67   cy = mpn_lshift (tp, xp + 2*n, n, 2);
  68   xp2[n] = cy + mpn_add_n (xp2, tp, xp, n);
  69
  70   tp[x3n] = mpn_lshift (tp, xp + 3*n, x3n, 2);
  71   if (x3n < n)
  72     tp[n] = mpn_add (tp, xp + n, n, tp, x3n + 1);
  73   else
  74     tp[n] += mpn_add_n (tp, xp + n, tp, n);
  75 #endif
  76   mpn_lshift (tp, tp, n+1, 1);
  77
  78   neg = (mpn_cmp (xp2, tp, n + 1) < 0) ? ~0 : 0;
  79
  80 #if HAVE_NATIVE_mpn_add_n_sub_n
  81   if (neg)
  82     mpn_add_n_sub_n (xp2, xm2, tp, xp2, n + 1);
  83   else
  84     mpn_add_n_sub_n (xp2, xm2, xp2, tp, n + 1);
  85 #else
  86   if (neg)
  87     mpn_sub_n (xm2, tp, xp2, n + 1);
  88   else
  89     mpn_sub_n (xm2, xp2, tp, n + 1);
  90
  91   mpn_add_n (xp2, xp2, tp, n + 1);
  92 #endif
  93
  94   ASSERT (xp2[n] < 15);
  95   ASSERT (xm2[n] < 10);
  96
  97   return neg;
  98 }