121 lines
3.3 KiB
C
121 lines
3.3 KiB
C
/* mpn_toom_eval_pm2 -- Evaluate a polynomial in +2 and -2
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Contributed to the GNU project by Niels Möller and Marco Bodrato
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THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE. IT IS ONLY
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SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST
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GUARANTEED THAT IT WILL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
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Copyright 2009 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
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#include "mpir.h"
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#include "gmp-impl.h"
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/* DO_addlsh2(d,a,b,n,cy) computes cy,{d,n} <- {a,n} + 4*(cy,{b,n}), it
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can be used as DO_addlsh2(d,a,d,n,d[n]), for accumulation on {d,n+1}. */
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#if HAVE_NATIVE_mpn_addlsh2_n
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#define DO_addlsh2(d, a, b, n, cy) \
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do { \
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(cy) <<= 2; \
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(cy) += mpn_addlsh2_n(d, a, b, n); \
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} while (0)
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#else
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#if HAVE_NATIVE_mpn_addlsh_n
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#define DO_addlsh2(d, a, b, n, cy) \
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do { \
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(cy) <<= 2; \
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(cy) += mpn_addlsh_n(d, a, b, n, 2); \
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} while (0)
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#else
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/* The following is not a general substitute for addlsh2.
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It is correct if d == b, but it is not if d == a. */
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#define DO_addlsh2(d, a, b, n, cy) \
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do { \
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(cy) <<= 2; \
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(cy) += mpn_lshift(d, b, n, 2); \
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(cy) += mpn_add_n(d, d, a, n); \
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} while (0)
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#endif
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#endif
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/* Evaluates a polynomial of degree 2 < k < GMP_NUMB_BITS, in the
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points +2 and -2. */
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int
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mpn_toom_eval_pm2 (mp_ptr xp2, mp_ptr xm2, unsigned k,
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mp_srcptr xp, mp_size_t n, mp_size_t hn, mp_ptr tp)
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{
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int i;
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int neg;
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mp_limb_t cy;
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ASSERT (k >= 3);
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ASSERT (k < GMP_NUMB_BITS);
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ASSERT (hn > 0);
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ASSERT (hn <= n);
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/* The degree k is also the number of full-size coefficients, so
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* that last coefficient, of size hn, starts at xp + k*n. */
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cy = 0;
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DO_addlsh2 (xp2, xp + (k-2) * n, xp + k * n, hn, cy);
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if (hn != n)
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cy = mpn_add_1 (xp2 + hn, xp + (k-2) * n + hn, n - hn, cy);
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for (i = k - 4; i >= 0; i -= 2)
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DO_addlsh2 (xp2, xp + i * n, xp2, n, cy);
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xp2[n] = cy;
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k--;
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cy = 0;
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DO_addlsh2 (tp, xp + (k-2) * n, xp + k * n, n, cy);
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for (i = k - 4; i >= 0; i -= 2)
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DO_addlsh2 (tp, xp + i * n, tp, n, cy);
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tp[n] = cy;
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if (k & 1)
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ASSERT_NOCARRY(mpn_lshift (tp , tp , n + 1, 1));
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else
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ASSERT_NOCARRY(mpn_lshift (xp2, xp2, n + 1, 1));
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neg = (mpn_cmp (xp2, tp, n + 1) < 0) ? ~0 : 0;
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#if HAVE_NATIVE_mpn_sumdiff_n
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if (neg)
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mpn_sumdiff_n (xp2, xm2, tp, xp2, n + 1);
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else
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mpn_sumdiff_n (xp2, xm2, xp2, tp, n + 1);
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#else
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if (neg)
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mpn_sub_n (xm2, tp, xp2, n + 1);
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else
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mpn_sub_n (xm2, xp2, tp, n + 1);
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mpn_add_n (xp2, xp2, tp, n + 1);
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#endif
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ASSERT (xp2[n] < (1<<(k+2))-1);
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ASSERT (xm2[n] < ((1<<(k+3))-1 - (1^k&1))/3);
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neg ^= ((k & 1) - 1);
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return neg;
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}
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#undef DO_addlsh2
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