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