toom_eval_pm2.c revision 1.1.1.1
1 /* mpn_toom_eval_pm2 -- Evaluate a polynomial in +2 and -2 2 3 Contributed to the GNU project by Niels Mller 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 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 #include "gmp.h" 27 #include "gmp-impl.h" 28 29 /* DO_addlsh2(d,a,b,n,cy) computes cy,{d,n} <- {a,n} + 4*(cy,{b,n}), it 30 can be used as DO_addlsh2(d,a,d,n,d[n]), for accumulation on {d,n+1}. */ 31 #if HAVE_NATIVE_mpn_addlsh2_n 32 #define DO_addlsh2(d, a, b, n, cy) \ 33 do { \ 34 (cy) <<= 2; \ 35 (cy) += mpn_addlsh2_n(d, a, b, n); \ 36 } while (0) 37 #else 38 #if HAVE_NATIVE_mpn_addlsh_n 39 #define DO_addlsh2(d, a, b, n, cy) \ 40 do { \ 41 (cy) <<= 2; \ 42 (cy) += mpn_addlsh_n(d, a, b, n, 2); \ 43 } while (0) 44 #else 45 /* The following is not a general substitute for addlsh2. 46 It is correct if d == b, but it is not if d == a. */ 47 #define DO_addlsh2(d, a, b, n, cy) \ 48 do { \ 49 (cy) <<= 2; \ 50 (cy) += mpn_lshift(d, b, n, 2); \ 51 (cy) += mpn_add_n(d, d, a, n); \ 52 } while (0) 53 #endif 54 #endif 55 56 /* Evaluates a polynomial of degree 2 < k < GMP_NUMB_BITS, in the 57 points +2 and -2. */ 58 int 59 mpn_toom_eval_pm2 (mp_ptr xp2, mp_ptr xm2, unsigned k, 60 mp_srcptr xp, mp_size_t n, mp_size_t hn, mp_ptr tp) 61 { 62 int i; 63 int neg; 64 mp_limb_t cy; 65 66 ASSERT (k >= 3); 67 ASSERT (k < GMP_NUMB_BITS); 68 69 ASSERT (hn > 0); 70 ASSERT (hn <= n); 71 72 /* The degree k is also the number of full-size coefficients, so 73 * that last coefficient, of size hn, starts at xp + k*n. */ 74 75 cy = 0; 76 DO_addlsh2 (xp2, xp + (k-2) * n, xp + k * n, hn, cy); 77 if (hn != n) 78 cy = mpn_add_1 (xp2 + hn, xp + (k-2) * n + hn, n - hn, cy); 79 for (i = k - 4; i >= 0; i -= 2) 80 DO_addlsh2 (xp2, xp + i * n, xp2, n, cy); 81 xp2[n] = cy; 82 83 k--; 84 85 cy = 0; 86 DO_addlsh2 (tp, xp + (k-2) * n, xp + k * n, n, cy); 87 for (i = k - 4; i >= 0; i -= 2) 88 DO_addlsh2 (tp, xp + i * n, tp, n, cy); 89 tp[n] = cy; 90 91 if (k & 1) 92 ASSERT_NOCARRY(mpn_lshift (tp , tp , n + 1, 1)); 93 else 94 ASSERT_NOCARRY(mpn_lshift (xp2, xp2, n + 1, 1)); 95 96 neg = (mpn_cmp (xp2, tp, n + 1) < 0) ? ~0 : 0; 97 98 #if HAVE_NATIVE_mpn_add_n_sub_n 99 if (neg) 100 mpn_add_n_sub_n (xp2, xm2, tp, xp2, n + 1); 101 else 102 mpn_add_n_sub_n (xp2, xm2, xp2, tp, n + 1); 103 #else /* !HAVE_NATIVE_mpn_add_n_sub_n */ 104 if (neg) 105 mpn_sub_n (xm2, tp, xp2, n + 1); 106 else 107 mpn_sub_n (xm2, xp2, tp, n + 1); 108 109 mpn_add_n (xp2, xp2, tp, n + 1); 110 #endif /* !HAVE_NATIVE_mpn_add_n_sub_n */ 111 112 ASSERT (xp2[n] < (1<<(k+2))-1); 113 ASSERT (xm2[n] < ((1<<(k+3))-1 - (1^k&1))/3); 114 115 neg ^= ((k & 1) - 1); 116 117 return neg; 118 } 119 120 #undef DO_addlsh2 121
Indexes created Tue Apr 21 00:23:25 UTC 2026