1 /* mpn_toom_eval_pm2 -- Evaluate a polynomial in +2 and -2
2
3 Contributed to the GNU project by Niels Möller and Marco Bodrato
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 #include "gmp-impl.h"
38
39 /* DO_addlsh2(d,a,b,n,cy) computes cy,{d,n} <- {a,n} + 4*(cy,{b,n}), it
40 can be used as DO_addlsh2(d,a,d,n,d[n]), for accumulation on {d,n+1}. */
41 #if HAVE_NATIVE_mpn_addlsh2_n
42 #define DO_addlsh2(d, a, b, n, cy) \
43 do { \
44 (cy) <<= 2; \
45 (cy) += mpn_addlsh2_n(d, a, b, n); \
46 } while (0)
47 #else
48 #if HAVE_NATIVE_mpn_addlsh_n
49 #define DO_addlsh2(d, a, b, n, cy) \
50 do { \
51 (cy) <<= 2; \
52 (cy) += mpn_addlsh_n(d, a, b, n, 2); \
53 } while (0)
54 #else
55 /* The following is not a general substitute for addlsh2.
56 It is correct if d == b, but it is not if d == a. */
57 #define DO_addlsh2(d, a, b, n, cy) \
58 do { \
59 (cy) <<= 2; \
60 (cy) += mpn_lshift(d, b, n, 2); \
61 (cy) += mpn_add_n(d, d, a, n); \
62 } while (0)
63 #endif
64 #endif
65
66 /* Evaluates a polynomial of degree 2 < k < GMP_NUMB_BITS, in the
67 points +2 and -2. */
68 int
69 mpn_toom_eval_pm2 (mp_ptr xp2, mp_ptr xm2, unsigned k,
70 mp_srcptr xp, mp_size_t n, mp_size_t hn, mp_ptr tp)
71 {
72 int i;
73 int neg;
74 mp_limb_t cy;
75
76 ASSERT (k >= 3);
77 ASSERT (k < GMP_NUMB_BITS);
78
79 ASSERT (hn > 0);
80 ASSERT (hn <= n);
81
82 /* The degree k is also the number of full-size coefficients, so
83 * that last coefficient, of size hn, starts at xp + k*n. */
84
85 cy = 0;
86 DO_addlsh2 (xp2, xp + (k-2) * n, xp + k * n, hn, cy);
87 if (hn != n)
88 cy = mpn_add_1 (xp2 + hn, xp + (k-2) * n + hn, n - hn, cy);
89 for (i = k - 4; i >= 0; i -= 2)
90 DO_addlsh2 (xp2, xp + i * n, xp2, n, cy);
91 xp2[n] = cy;
92
93 k--;
94
95 cy = 0;
96 DO_addlsh2 (tp, xp + (k-2) * n, xp + k * n, n, cy);
97 for (i = k - 4; i >= 0; i -= 2)
98 DO_addlsh2 (tp, xp + i * n, tp, n, cy);
99 tp[n] = cy;
100
101 if (k & 1)
102 ASSERT_NOCARRY(mpn_lshift (tp , tp , n + 1, 1));
103 else
104 ASSERT_NOCARRY(mpn_lshift (xp2, xp2, n + 1, 1));
105
106 neg = (mpn_cmp (xp2, tp, n + 1) < 0) ? ~0 : 0;
107
108 #if HAVE_NATIVE_mpn_add_n_sub_n
109 if (neg)
110 mpn_add_n_sub_n (xp2, xm2, tp, xp2, n + 1);
111 else
112 mpn_add_n_sub_n (xp2, xm2, xp2, tp, n + 1);
113 #else /* !HAVE_NATIVE_mpn_add_n_sub_n */
114 if (neg)
115 mpn_sub_n (xm2, tp, xp2, n + 1);
116 else
117 mpn_sub_n (xm2, xp2, tp, n + 1);
118
119 mpn_add_n (xp2, xp2, tp, n + 1);
120 #endif /* !HAVE_NATIVE_mpn_add_n_sub_n */
121
122 ASSERT (xp2[n] < (1<<(k+2))-1);
123 ASSERT (xm2[n] < ((1<<(k+3))-1 - (1^k&1))/3);
124
125 neg ^= ((k & 1) - 1);
126
127 return neg;
128 }
129
130 #undef DO_addlsh2