43 lines
1.3 KiB
C
43 lines
1.3 KiB
C
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/* Copyright (c) 2016, Google Inc.
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
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#include "internal.h"
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/* Incomplete-reduction routines; for details on allowed input ranges
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* and produced output ranges, see the description in the paper:
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* https://cryptojedi.org/papers/#newhope */
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static const uint32_t kQInv = 12287; /* -inverse_mod(p,2^18) */
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static const uint32_t kRLog = 18;
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uint16_t newhope_montgomery_reduce(uint32_t a) {
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uint32_t u;
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u = (a * kQInv);
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u &= ((1 << kRLog) - 1);
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u *= PARAM_Q;
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a = a + u;
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return a >> 18;
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}
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uint16_t newhope_barrett_reduce(uint16_t a) {
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uint32_t u;
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u = ((uint32_t)a * 5) >> 16;
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u *= PARAM_Q;
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a -= u;
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return a;
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}
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