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Annotation of embedaddon/strongswan/src/libstrongswan/math/libnttfft/ntt_fft_reduce.h, revision 1.1

1.1     ! misho       1: /*
        !             2:  * Copyright (C) 2016 Andreas Steffen
        !             3:  * HSR Hochschule fuer Technik Rapperswil
        !             4:  *
        !             5:  * This program is free software; you can redistribute it and/or modify it
        !             6:  * under the terms of the GNU General Public License as published by the
        !             7:  * Free Software Foundation; either version 2 of the License, or (at your
        !             8:  * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
        !             9:  *
        !            10:  * This program is distributed in the hope that it will be useful, but
        !            11:  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
        !            12:  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
        !            13:  * for more details.
        !            14:  */
        !            15: 
        !            16: /**
        !            17:  * @defgroup ntt_fft ntt_fft
        !            18:  * @{ @ingroup ntt_p
        !            19:  */
        !            20: 
        !            21: #ifndef NTT_REDUCE_H_
        !            22: #define NTT_REDUCE_H_
        !            23: 
        !            24: #include "ntt_fft_params.h"
        !            25: 
        !            26: /**
        !            27:  * Montgomery Reduction
        !            28:  *
        !            29:  * Montgomery, P. L. Modular multiplication without trial division.
        !            30:  * Mathematics of Computation 44, 170 (1985), 519–521.
        !            31:  */
        !            32: static inline uint32_t ntt_fft_mreduce(uint32_t x, const ntt_fft_params_t *p)
        !            33: {
        !            34:        uint32_t m, t;
        !            35: 
        !            36:        m = (x * p->q_inv) & p->rmask;
        !            37:        t = (x + m * p->q) >> p->rlog;
        !            38: 
        !            39:        return (t < p->q) ? t : t - p->q;
        !            40: }
        !            41: 
        !            42: #endif /** NTT_REDUCE_H_ @}*/