83 lines
2.4 KiB
C
83 lines
2.4 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 Fredrik Johansson
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******************************************************************************/
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#include <gmp.h>
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#include "flint.h"
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#include "ulong_extras.h"
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static const mp_limb_t small_factorials[] =
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{
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UWORD(1), UWORD(1), UWORD(2), UWORD(6), UWORD(24), UWORD(120), UWORD(720), UWORD(5040), UWORD(40320), UWORD(362880),
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UWORD(3628800), UWORD(39916800), UWORD(479001600),
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#if FLINT64
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UWORD(6227020800), UWORD(87178291200),
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UWORD(1307674368000), UWORD(20922789888000), UWORD(355687428096000), UWORD(6402373705728000),
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UWORD(121645100408832000), UWORD(2432902008176640000),
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#endif
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};
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#if FLINT64
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#define MAX_SMALL_FACTORIAL 20
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#else
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#define MAX_SMALL_FACTORIAL 12
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#endif
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mp_limb_t n_factorial_mod2_preinv(ulong n, mp_limb_t p, mp_limb_t pinv)
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{
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mp_limb_t prod, hi, lo;
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if (n <= MAX_SMALL_FACTORIAL)
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return n_mod2_preinv(small_factorials[n], p, pinv);
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if (n >= p)
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return UWORD(0);
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if (n >= UWORD(1000000))
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return n_factorial_fast_mod2_preinv(n, p, pinv);
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prod = small_factorials[MAX_SMALL_FACTORIAL];
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lo = n;
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n--;
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/* TODO: speedup for n in the range of sqrt(UWORD_MAX) */
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while (n > MAX_SMALL_FACTORIAL)
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{
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umul_ppmm(hi, lo, lo, n);
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if (hi)
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{
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lo = n_ll_mod_preinv(hi, lo, p, pinv);
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prod = n_mulmod2_preinv(prod, lo, p, pinv);
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lo = UWORD(1);
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}
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n--;
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}
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return n_mulmod2_preinv(prod, lo, p, pinv);
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}
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