mpir/mpn/generic/toom_eval_pm2.c
2010-02-16 23:47:07 +00:00

121 lines
3.3 KiB
C

/* mpn_toom_eval_pm2 -- Evaluate a polynomial in +2 and -2
Contributed to the GNU project by Niels Möller and Marco Bodrato
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 "mpir.h"
#include "gmp-impl.h"
/* DO_addlsh2(d,a,b,n,cy) computes cy,{d,n} <- {a,n} + 4*(cy,{b,n}), it
can be used as DO_addlsh2(d,a,d,n,d[n]), for accumulation on {d,n+1}. */
#if HAVE_NATIVE_mpn_addlsh2_n
#define DO_addlsh2(d, a, b, n, cy) \
do { \
(cy) <<= 2; \
(cy) += mpn_addlsh2_n(d, a, b, n); \
} while (0)
#else
#if HAVE_NATIVE_mpn_addlsh_n
#define DO_addlsh2(d, a, b, n, cy) \
do { \
(cy) <<= 2; \
(cy) += mpn_addlsh_n(d, a, b, n, 2); \
} while (0)
#else
/* The following is not a general substitute for addlsh2.
It is correct if d == b, but it is not if d == a. */
#define DO_addlsh2(d, a, b, n, cy) \
do { \
(cy) <<= 2; \
(cy) += mpn_lshift(d, b, n, 2); \
(cy) += mpn_add_n(d, d, a, n); \
} while (0)
#endif
#endif
/* Evaluates a polynomial of degree 2 < k < GMP_NUMB_BITS, in the
points +2 and -2. */
int
mpn_toom_eval_pm2 (mp_ptr xp2, mp_ptr xm2, unsigned k,
mp_srcptr xp, mp_size_t n, mp_size_t hn, mp_ptr tp)
{
int i;
int neg;
mp_limb_t cy;
ASSERT (k >= 3);
ASSERT (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. */
cy = 0;
DO_addlsh2 (xp2, xp + (k-2) * n, xp + k * n, hn, cy);
if (hn != n)
cy = mpn_add_1 (xp2 + hn, xp + (k-2) * n + hn, n - hn, cy);
for (i = k - 4; i >= 0; i -= 2)
DO_addlsh2 (xp2, xp + i * n, xp2, n, cy);
xp2[n] = cy;
k--;
cy = 0;
DO_addlsh2 (tp, xp + (k-2) * n, xp + k * n, n, cy);
for (i = k - 4; i >= 0; i -= 2)
DO_addlsh2 (tp, xp + i * n, tp, n, cy);
tp[n] = cy;
if (k & 1)
ASSERT_NOCARRY(mpn_lshift (tp , tp , n + 1, 1));
else
ASSERT_NOCARRY(mpn_lshift (xp2, xp2, n + 1, 1));
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 */
ASSERT (xp2[n] < (1<<(k+2))-1);
ASSERT (xm2[n] < ((1<<(k+3))-1 - (1^k&1))/3);
neg ^= ((k & 1) - 1);
return neg;
}
#undef DO_addlsh2