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
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 the GNU Lesser General Public License as published by
15 the Free Software Foundation; either version 3 of the License, or (at your
16 option) any later version.
17
18 The GNU MP Library is distributed in the hope that it will be useful, but
19 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
20 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
21 License for more details.
22
23 You should have received a copy of the GNU Lesser General Public License
24 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
25
26
27 #include "gmp.h"
28 #include "gmp-impl.h"
29
30 /* Evaluates a polynomial of degree k > 2, in the points +2^shift and -2^shift. */
31 int
mpn_toom_eval_pm2exp(mp_ptr xp2,mp_ptr xm2,unsigned k,mp_srcptr xp,mp_size_t n,mp_size_t hn,unsigned shift,mp_ptr tp)32 mpn_toom_eval_pm2exp (mp_ptr xp2, mp_ptr xm2, unsigned k,
33 mp_srcptr xp, mp_size_t n, mp_size_t hn, unsigned shift,
34 mp_ptr tp)
35 {
36 unsigned i;
37 int neg;
38 #if HAVE_NATIVE_mpn_addlsh_n
39 mp_limb_t cy;
40 #endif
41
42 ASSERT (k >= 3);
43 ASSERT (shift*k < GMP_NUMB_BITS);
44
45 ASSERT (hn > 0);
46 ASSERT (hn <= n);
47
48 /* The degree k is also the number of full-size coefficients, so
49 * that last coefficient, of size hn, starts at xp + k*n. */
50
51 #if HAVE_NATIVE_mpn_addlsh_n
52 xp2[n] = mpn_addlsh_n (xp2, xp, xp + 2*n, n, 2*shift);
53 for (i = 4; i < k; i += 2)
54 xp2[n] += mpn_addlsh_n (xp2, xp2, xp + i*n, n, i*shift);
55
56 tp[n] = mpn_lshift (tp, xp+n, n, shift);
57 for (i = 3; i < k; i+= 2)
58 tp[n] += mpn_addlsh_n (tp, tp, xp+i*n, n, i*shift);
59
60 if (k & 1)
61 {
62 cy = mpn_addlsh_n (tp, tp, xp+k*n, hn, k*shift);
63 MPN_INCR_U (tp + hn, n+1 - hn, cy);
64 }
65 else
66 {
67 cy = mpn_addlsh_n (xp2, xp2, xp+k*n, hn, k*shift);
68 MPN_INCR_U (xp2 + hn, n+1 - hn, cy);
69 }
70
71 #else /* !HAVE_NATIVE_mpn_addlsh_n */
72 xp2[n] = mpn_lshift (tp, xp+2*n, n, 2*shift);
73 xp2[n] += mpn_add_n (xp2, xp, tp, n);
74 for (i = 4; i < k; i += 2)
75 {
76 xp2[n] += mpn_lshift (tp, xp + i*n, n, i*shift);
77 xp2[n] += mpn_add_n (xp2, xp2, tp, n);
78 }
79
80 tp[n] = mpn_lshift (tp, xp+n, n, shift);
81 for (i = 3; i < k; i+= 2)
82 {
83 tp[n] += mpn_lshift (xm2, xp + i*n, n, i*shift);
84 tp[n] += mpn_add_n (tp, tp, xm2, n);
85 }
86
87 xm2[hn] = mpn_lshift (xm2, xp + k*n, hn, k*shift);
88 if (k & 1)
89 mpn_add (tp, tp, n+1, xm2, hn+1);
90 else
91 mpn_add (xp2, xp2, n+1, xm2, hn+1);
92 #endif /* !HAVE_NATIVE_mpn_addlsh_n */
93
94 neg = (mpn_cmp (xp2, tp, n + 1) < 0) ? ~0 : 0;
95
96 #if HAVE_NATIVE_mpn_add_n_sub_n
97 if (neg)
98 mpn_add_n_sub_n (xp2, xm2, tp, xp2, n + 1);
99 else
100 mpn_add_n_sub_n (xp2, xm2, xp2, tp, n + 1);
101 #else /* !HAVE_NATIVE_mpn_add_n_sub_n */
102 if (neg)
103 mpn_sub_n (xm2, tp, xp2, n + 1);
104 else
105 mpn_sub_n (xm2, xp2, tp, n + 1);
106
107 mpn_add_n (xp2, xp2, tp, n + 1);
108 #endif /* !HAVE_NATIVE_mpn_add_n_sub_n */
109
110 /* FIXME: the following asserts are useless if (k+1)*shift >= GMP_LIMB_BITS */
111 ASSERT ((k+1)*shift >= GMP_LIMB_BITS ||
112 xp2[n] < ((CNST_LIMB(1)<<((k+1)*shift))-1)/((CNST_LIMB(1)<<shift)-1));
113 ASSERT ((k+2)*shift >= GMP_LIMB_BITS ||
114 xm2[n] < ((CNST_LIMB(1)<<((k+2)*shift))-((k&1)?(CNST_LIMB(1)<<shift):1))/((CNST_LIMB(1)<<(2*shift))-1));
115
116 return neg;
117 }
118