73 lines
2.1 KiB
C
73 lines
2.1 KiB
C
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/*=============================================================================
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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) 2009, 2010 William Hart
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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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/*
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mp_limb_t n_mod2_preinv(mp_limb_t a, mp_limb_t n, mp_limb_t ninv)
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{
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unsigned int norm;
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mp_limb_t q, r;
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count_leading_zeros(norm, n);
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udiv_qrnnd_preinv(q, r, r_shift(a, FLINT_BITS-norm), a<<norm, n<<norm, ninv);
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return (r>>norm);
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}
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*/
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/*
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New method of Moller and Granlund
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see paper Improved Division by Invariant Integers (Torbjorn Granlund
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and Niels Moller) (preprint): (pp. 4)
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http://www.lysator.liu.se/~nisse/archive/draft-division-paper.pdf
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*/
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mp_limb_t n_mod2_preinv(mp_limb_t a, mp_limb_t n, mp_limb_t ninv)
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{
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unsigned int norm;
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mp_limb_t q1, q0, r;
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count_leading_zeros(norm, n);
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n <<= norm;
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{
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const mp_limb_t u1 = r_shift(a, FLINT_BITS-norm);
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const mp_limb_t u0 = (a << norm);
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umul_ppmm(q1, q0, ninv, u1);
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add_ssaaaa(q1, q0, q1, q0, u1, u0);
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r = (u0 - (q1 + 1)*n);
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if (r >= q0) r += n;
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return (r < n) ? (r >> norm) : ((r - n) >> norm);
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}
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}
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