165 lines
4.2 KiB
C
165 lines
4.2 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) 2010 Sebastian Pancratz
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Copyright (C) 2010 William Hart
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******************************************************************************/
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#include <stdlib.h>
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#include <gmp.h>
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#include "flint.h"
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#include "nmod_vec.h"
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#include "nmod_poly.h"
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void
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_nmod_poly_pow_binexp(mp_ptr res, mp_srcptr poly, slong len, ulong e, nmod_t mod)
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{
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ulong bit = ~((~UWORD(0)) >> 1);
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slong rlen;
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slong alloc = (slong) e * (len - 1) + 1;
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mp_ptr v = _nmod_vec_init(alloc);
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mp_ptr R, S, T;
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/*
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Set bits to the bitmask with a 1 one place lower than the msb of e
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*/
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while ((bit & e) == UWORD(0))
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bit >>= 1;
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bit >>= 1;
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/*
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Trial run without any polynomial arithmetic to determine the parity
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of the number of swaps; then set R and S accordingly
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*/
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{
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unsigned int swaps = 0U;
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ulong bit2 = bit;
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if ((bit2 & e))
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swaps = ~swaps;
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while (bit2 >>= 1)
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if ((bit2 & e) == UWORD(0))
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swaps = ~swaps;
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if (swaps == 0U)
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{
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R = res;
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S = v;
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}
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else
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{
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R = v;
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S = res;
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}
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}
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/*
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We unroll the first step of the loop, referring to {poly, len}
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*/
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_nmod_poly_mul(R, poly, len, poly, len, mod);
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rlen = 2 * len - 1;
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if ((bit & e))
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{
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_nmod_poly_mul(S, R, rlen, poly, len, mod);
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rlen += len - 1;
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T = R;
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R = S;
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S = T;
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}
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while ((bit >>= 1))
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{
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if ((bit & e))
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{
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_nmod_poly_mul(S, R, rlen, R, rlen, mod);
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rlen += rlen - 1;
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_nmod_poly_mul(R, S, rlen, poly, len, mod);
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rlen += len - 1;
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}
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else
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{
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_nmod_poly_mul(S, R, rlen, R, rlen, mod);
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rlen += rlen - 1;
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T = R;
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R = S;
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S = T;
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}
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}
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_nmod_vec_clear(v);
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}
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void
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nmod_poly_pow_binexp(nmod_poly_t res, const nmod_poly_t poly, ulong e)
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{
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const slong len = poly->length;
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slong rlen;
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if ((len < 2) | (e < UWORD(3)))
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{
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if (len == 0)
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nmod_poly_zero(res);
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else if (len == 1)
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{
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nmod_poly_fit_length(res, 1);
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res->coeffs[0] = n_powmod2_preinv(poly->coeffs[0], e,
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poly->mod.n, poly->mod.ninv);
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res->length = 1;
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_nmod_poly_normalise(res);
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}
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else if (e == UWORD(0))
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{
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nmod_poly_set_coeff_ui(res, 0, UWORD(1));
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res->length = 1;
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_nmod_poly_normalise(res);
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}
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else if (e == UWORD(1))
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nmod_poly_set(res, poly);
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else /* e == UWORD(2) */
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nmod_poly_mul(res, poly, poly);
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return;
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}
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rlen = (slong) e * (len - 1) + 1;
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if (res != poly)
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{
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nmod_poly_fit_length(res, rlen);
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_nmod_poly_pow_binexp(res->coeffs, poly->coeffs, len, e, poly->mod);
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}
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else
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{
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nmod_poly_t t;
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nmod_poly_init2(t, poly->mod.n, rlen);
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_nmod_poly_pow_binexp(t->coeffs, poly->coeffs, len, e, poly->mod);
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nmod_poly_swap(res, t);
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nmod_poly_clear(t);
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}
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res->length = rlen;
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_nmod_poly_normalise(res);
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}
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