toom_eval_pm2exp.c
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- /* mpn_toom_eval_pm2exp -- Evaluate a polynomial in +2^k and -2^k
- Contributed to the GNU project by Niels M鰈ler
- THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE. IT IS ONLY
- SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST
- GUARANTEED THAT IT WILL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
- Copyright 2009 Free Software Foundation, Inc.
- This file is part of the GNU MP Library.
- The GNU MP Library is free software; you can redistribute it and/or modify
- it under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 3 of the License, or (at your
- option) any later version.
- The GNU MP Library is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
- License for more details.
- You should have received a copy of the GNU Lesser General Public License
- along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
- #include "gmp.h"
- #include "gmp-impl.h"
- /* Evaluates a polynomial of degree k > 2, in the points +2^shift and -2^shift. */
- 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)
- {
- unsigned i;
- int neg;
- #if HAVE_NATIVE_mpn_addlsh_n
- mp_limb_t cy;
- #endif
- ASSERT (k >= 3);
- ASSERT (shift*k < GMP_NUMB_BITS);
- ASSERT (hn > 0);
- ASSERT (hn <= n);
- /* The degree k is also the number of full-size coefficients, so
- * that last coefficient, of size hn, starts at xp + k*n. */
- #if HAVE_NATIVE_mpn_addlsh_n
- xp2[n] = mpn_addlsh_n (xp2, xp, xp + 2*n, n, 2*shift);
- for (i = 4; i < k; i += 2)
- xp2[n] += mpn_addlsh_n (xp2, xp2, xp + i*n, n, i*shift);
- tp[n] = mpn_lshift (tp, xp+n, n, shift);
- for (i = 3; i < k; i+= 2)
- tp[n] += mpn_addlsh_n (tp, tp, xp+i*n, n, i*shift);
- if (k & 1)
- {
- cy = mpn_addlsh_n (tp, tp, xp+k*n, hn, k*shift);
- MPN_INCR_U (tp + hn, n+1 - hn, cy);
- }
- else
- {
- cy = mpn_addlsh_n (xp2, xp2, xp+k*n, hn, k*shift);
- MPN_INCR_U (xp2 + hn, n+1 - hn, cy);
- }
- #else /* !HAVE_NATIVE_mpn_addlsh_n */
- xp2[n] = mpn_lshift (tp, xp+2*n, n, 2*shift);
- xp2[n] += mpn_add_n (xp2, xp, tp, n);
- for (i = 4; i < k; i += 2)
- {
- xp2[n] += mpn_lshift (tp, xp + i*n, n, i*shift);
- xp2[n] += mpn_add_n (xp2, xp2, tp, n);
- }
- tp[n] = mpn_lshift (tp, xp+n, n, shift);
- for (i = 3; i < k; i+= 2)
- {
- tp[n] += mpn_lshift (xm2, xp + i*n, n, i*shift);
- tp[n] += mpn_add_n (tp, tp, xm2, n);
- }
- xm2[hn] = mpn_lshift (xm2, xp + k*n, hn, k*shift);
- if (k & 1)
- mpn_add (tp, tp, n+1, xm2, hn+1);
- else
- mpn_add (xp2, xp2, n+1, xm2, hn+1);
- #endif /* !HAVE_NATIVE_mpn_addlsh_n */
- neg = (mpn_cmp (xp2, tp, n + 1) < 0) ? ~0 : 0;
- #if HAVE_NATIVE_mpn_add_n_sub_n
- if (neg)
- mpn_add_n_sub_n (xp2, xm2, tp, xp2, n + 1);
- else
- mpn_add_n_sub_n (xp2, xm2, xp2, tp, n + 1);
- #else /* !HAVE_NATIVE_mpn_add_n_sub_n */
- if (neg)
- mpn_sub_n (xm2, tp, xp2, n + 1);
- else
- mpn_sub_n (xm2, xp2, tp, n + 1);
- mpn_add_n (xp2, xp2, tp, n + 1);
- #endif /* !HAVE_NATIVE_mpn_add_n_sub_n */
- /* FIXME: the following asserts are useless if (k+1)*shift >= GMP_LIMB_BITS */
- ASSERT ((k+1)*shift >= GMP_LIMB_BITS ||
- xp2[n] < ((CNST_LIMB(1)<<((k+1)*shift))-1)/((CNST_LIMB(1)<<shift)-1));
- ASSERT ((k+2)*shift >= GMP_LIMB_BITS ||
- xm2[n] < ((CNST_LIMB(1)<<((k+2)*shift))-((k&1)?(CNST_LIMB(1)<<shift):1))/((CNST_LIMB(1)<<(2*shift))-1));
- return neg;
- }