1/* mpn_toom_eval_dgr3_pm2 -- Evaluate a degree 3 polynomial in +2 and -2
2
3   Contributed to the GNU project by Niels M��ller
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
9Copyright 2009 Free Software Foundation, Inc.
10
11This file is part of the GNU MP Library.
12
13The GNU MP Library is free software; you can redistribute it and/or modify
14it 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
20or
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
26or both in parallel, as here.
27
28The GNU MP Library is distributed in the hope that it will be useful, but
29WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
30or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
31for more details.
32
33You should have received copies of the GNU General Public License and the
34GNU Lesser General Public License along with the GNU MP Library.  If not,
35see https://www.gnu.org/licenses/.  */
36
37
38#include "gmp-impl.h"
39
40/* Needs n+1 limbs of temporary storage. */
41int
42mpn_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}
98