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.h"
39 #include "gmp-impl.h"
40
41 /* Evaluates a polynomial of degree k > 3, in the points +1 and -1. */
42 int
mpn_toom_eval_pm1(mp_ptr xp1,mp_ptr xm1,unsigned k,mp_srcptr xp,mp_size_t n,mp_size_t hn,mp_ptr tp)43 mpn_toom_eval_pm1 (mp_ptr xp1, mp_ptr xm1, unsigned k,
44 mp_srcptr xp, mp_size_t n, mp_size_t hn, mp_ptr tp)
45 {
46 unsigned i;
47 int neg;
48
49 ASSERT (k >= 4);
50
51 ASSERT (hn > 0);
52 ASSERT (hn <= n);
53
54 /* The degree k is also the number of full-size coefficients, so
55 * that last coefficient, of size hn, starts at xp + k*n. */
56
57 xp1[n] = mpn_add_n (xp1, xp, xp + 2*n, n);
58 for (i = 4; i < k; i += 2)
59 ASSERT_NOCARRY (mpn_add (xp1, xp1, n+1, xp+i*n, n));
60
61 tp[n] = mpn_add_n (tp, xp + n, xp + 3*n, n);
62 for (i = 5; i < k; i += 2)
63 ASSERT_NOCARRY (mpn_add (tp, tp, n+1, xp+i*n, n));
64
65 if (k & 1)
66 ASSERT_NOCARRY (mpn_add (tp, tp, n+1, xp+k*n, hn));
67 else
68 ASSERT_NOCARRY (mpn_add (xp1, xp1, n+1, xp+k*n, hn));
69
70 neg = (mpn_cmp (xp1, tp, n + 1) < 0) ? ~0 : 0;
71
72 #if HAVE_NATIVE_mpn_add_n_sub_n
73 if (neg)
74 mpn_add_n_sub_n (xp1, xm1, tp, xp1, n + 1);
75 else
76 mpn_add_n_sub_n (xp1, xm1, xp1, tp, n + 1);
77 #else
78 if (neg)
79 mpn_sub_n (xm1, tp, xp1, n + 1);
80 else
81 mpn_sub_n (xm1, xp1, tp, n + 1);
82
83 mpn_add_n (xp1, xp1, tp, n + 1);
84 #endif
85
86 ASSERT (xp1[n] <= k);
87 ASSERT (xm1[n] <= k/2 + 1);
88
89 return neg;
90 }
91