1/* mpn_toom_eval_pm2exp -- Evaluate a polynomial in +2^k and -2^k
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/* Evaluates a polynomial of degree k > 2, in the points +2^shift and -2^shift. */
41int
42mpn_toom_eval_pm2exp (mp_ptr xp2, mp_ptr xm2, unsigned k,
43		      mp_srcptr xp, mp_size_t n, mp_size_t hn, unsigned shift,
44		      mp_ptr tp)
45{
46  unsigned i;
47  int neg;
48#if HAVE_NATIVE_mpn_addlsh_n
49  mp_limb_t cy;
50#endif
51
52  ASSERT (k >= 3);
53  ASSERT (shift*k < GMP_NUMB_BITS);
54
55  ASSERT (hn > 0);
56  ASSERT (hn <= n);
57
58  /* The degree k is also the number of full-size coefficients, so
59   * that last coefficient, of size hn, starts at xp + k*n. */
60
61#if HAVE_NATIVE_mpn_addlsh_n
62  xp2[n] = mpn_addlsh_n (xp2, xp, xp + 2*n, n, 2*shift);
63  for (i = 4; i < k; i += 2)
64    xp2[n] += mpn_addlsh_n (xp2, xp2, xp + i*n, n, i*shift);
65
66  tp[n] = mpn_lshift (tp, xp+n, n, shift);
67  for (i = 3; i < k; i+= 2)
68    tp[n] += mpn_addlsh_n (tp, tp, xp+i*n, n, i*shift);
69
70  if (k & 1)
71    {
72      cy = mpn_addlsh_n (tp, tp, xp+k*n, hn, k*shift);
73      MPN_INCR_U (tp + hn, n+1 - hn, cy);
74    }
75  else
76    {
77      cy = mpn_addlsh_n (xp2, xp2, xp+k*n, hn, k*shift);
78      MPN_INCR_U (xp2 + hn, n+1 - hn, cy);
79    }
80
81#else /* !HAVE_NATIVE_mpn_addlsh_n */
82  xp2[n] = mpn_lshift (tp, xp+2*n, n, 2*shift);
83  xp2[n] += mpn_add_n (xp2, xp, tp, n);
84  for (i = 4; i < k; i += 2)
85    {
86      xp2[n] += mpn_lshift (tp, xp + i*n, n, i*shift);
87      xp2[n] += mpn_add_n (xp2, xp2, tp, n);
88    }
89
90  tp[n] = mpn_lshift (tp, xp+n, n, shift);
91  for (i = 3; i < k; i+= 2)
92    {
93      tp[n] += mpn_lshift (xm2, xp + i*n, n, i*shift);
94      tp[n] += mpn_add_n (tp, tp, xm2, n);
95    }
96
97  xm2[hn] = mpn_lshift (xm2, xp + k*n, hn, k*shift);
98  if (k & 1)
99    mpn_add (tp, tp, n+1, xm2, hn+1);
100  else
101    mpn_add (xp2, xp2, n+1, xm2, hn+1);
102#endif /* !HAVE_NATIVE_mpn_addlsh_n */
103
104  neg = (mpn_cmp (xp2, tp, n + 1) < 0) ? ~0 : 0;
105
106#if HAVE_NATIVE_mpn_add_n_sub_n
107  if (neg)
108    mpn_add_n_sub_n (xp2, xm2, tp, xp2, n + 1);
109  else
110    mpn_add_n_sub_n (xp2, xm2, xp2, tp, n + 1);
111#else /* !HAVE_NATIVE_mpn_add_n_sub_n */
112  if (neg)
113    mpn_sub_n (xm2, tp, xp2, n + 1);
114  else
115    mpn_sub_n (xm2, xp2, tp, n + 1);
116
117  mpn_add_n (xp2, xp2, tp, n + 1);
118#endif /* !HAVE_NATIVE_mpn_add_n_sub_n */
119
120  /* FIXME: the following asserts are useless if (k+1)*shift >= GMP_LIMB_BITS */
121  ASSERT ((k+1)*shift >= GMP_LIMB_BITS ||
122	  xp2[n] < ((CNST_LIMB(1)<<((k+1)*shift))-1)/((CNST_LIMB(1)<<shift)-1));
123  ASSERT ((k+2)*shift >= GMP_LIMB_BITS ||
124	  xm2[n] < ((CNST_LIMB(1)<<((k+2)*shift))-((k&1)?(CNST_LIMB(1)<<shift):1))/((CNST_LIMB(1)<<(2*shift))-1));
125
126  return neg;
127}
128