43 lines
1.1 KiB
C
43 lines
1.1 KiB
C
/*
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* Copyright (C) 2016 Andreas Steffen
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* HSR Hochschule fuer Technik Rapperswil
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation; either version 2 of the License, or (at your
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* option) any later version. See <http://www.fsf.org/copyleft/gpl.txt>.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* for more details.
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*/
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/**
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* @defgroup ntt_fft ntt_fft
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* @{ @ingroup ntt_p
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*/
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#ifndef NTT_REDUCE_H_
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#define NTT_REDUCE_H_
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#include "ntt_fft_params.h"
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/**
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* Montgomery Reduction
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*
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* Montgomery, P. L. Modular multiplication without trial division.
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* Mathematics of Computation 44, 170 (1985), 519–521.
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*/
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static inline uint32_t ntt_fft_mreduce(uint32_t x, const ntt_fft_params_t *p)
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{
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uint32_t m, t;
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m = (x * p->q_inv) & p->rmask;
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t = (x + m * p->q) >> p->rlog;
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return (t < p->q) ? t : t - p->q;
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}
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#endif /** NTT_REDUCE_H_ @}*/
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