59 lines
1.7 KiB
C
59 lines
1.7 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, 2012 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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mp_limb_t
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n_mulmod_preinv(mp_limb_t a, mp_limb_t b, mp_limb_t n,
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mp_limb_t ninv, ulong norm)
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{
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mp_limb_t q0, q1, r, p_hi, p_lo;
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/* multiply */
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umul_ppmm(p_hi, p_lo, a, b);
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/* renormalise product */
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if (norm)
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{
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p_lo = (p_lo >> norm) + (p_hi << (FLINT_BITS - norm));
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p_hi = (p_hi >> norm);
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}
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/* reduce mod n */
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{
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umul_ppmm(q1, q0, ninv, p_hi);
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add_ssaaaa(q1, q0, q1, q0, p_hi, p_lo);
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r = (p_lo - (q1 + 1) * n);
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if (r >= q0)
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r += n;
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return (r < n ? r : r - n);
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}
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}
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