131 lines
3.3 KiB
C
131 lines
3.3 KiB
C
/*=============================================================================
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This file is part of FLINT.
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FLINT is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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FLINT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with FLINT; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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=============================================================================*/
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/******************************************************************************
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Copyright (C) 2011 William Hart
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Copyright (C) 2011 Fredrik Johansson
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******************************************************************************/
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#include <stdlib.h>
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#include "nmod_poly.h"
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#include "ulong_extras.h"
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static void
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__nmod_poly_invsqrt_series_prealloc(mp_ptr g,
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mp_srcptr h, mp_ptr t, mp_ptr u,
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slong n, nmod_t mod)
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{
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const int alloc = (t == NULL);
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const slong m = (n + 1) / 2;
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mp_limb_t c;
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if (n == 1)
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{
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g[0] = UWORD(1);
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return;
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}
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if (alloc)
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{
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t = _nmod_vec_init(n);
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u = _nmod_vec_init(n);
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}
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__nmod_poly_invsqrt_series_prealloc(g, h, t, u, m, mod);
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_nmod_vec_zero(g + m, n - m);
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_nmod_poly_mul(t, g, m, g, m, mod);
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if (2*m - 1 < n)
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t[n-1] = UWORD(0);
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_nmod_poly_mullow(u, t, n, g, n, n, mod);
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_nmod_poly_mullow(t, u, n, h, n, n, mod);
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c = n_invmod(mod.n - UWORD(2), mod.n);
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_nmod_vec_scalar_mul_nmod(g + m, t + m, n - m, c, mod);
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if (alloc)
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{
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_nmod_vec_clear(t);
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_nmod_vec_clear(u);
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}
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}
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void _nmod_poly_invsqrt_series(mp_ptr g, mp_srcptr h, slong n, nmod_t mod)
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{
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__nmod_poly_invsqrt_series_prealloc(g, h, NULL, NULL, n, mod);
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}
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void nmod_poly_invsqrt_series(nmod_poly_t g, const nmod_poly_t h, slong n)
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{
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const slong hlen = h->length;
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mp_ptr g_coeffs, h_coeffs;
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nmod_poly_t t1;
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if (n == 0 || h->length == 0 || h->coeffs[0] == 0)
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{
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flint_printf("Exception (nmod_poly_invsqrt). Division by zero.\n");
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abort();
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}
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if (h->coeffs[0] != UWORD(1))
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{
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flint_printf("Exception (nmod_poly_invsqrt_series). Constant term != 1.\n");
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abort();
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}
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if (hlen < n)
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{
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h_coeffs = _nmod_vec_init(n);
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flint_mpn_copyi(h_coeffs, h->coeffs, hlen);
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flint_mpn_zero(h_coeffs + hlen, n - hlen);
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}
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else
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h_coeffs = h->coeffs;
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if (h == g && hlen >= n)
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{
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nmod_poly_init2(t1, h->mod.n, n);
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g_coeffs = t1->coeffs;
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}
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else
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{
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nmod_poly_fit_length(g, n);
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g_coeffs = g->coeffs;
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}
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_nmod_poly_invsqrt_series(g_coeffs, h_coeffs, n, h->mod);
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if (h == g && hlen >= n)
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{
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nmod_poly_swap(g, t1);
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nmod_poly_clear(t1);
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}
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g->length = n;
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if (hlen < n)
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_nmod_vec_clear(h_coeffs);
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_nmod_poly_normalise(g);
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}
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