50 lines
1.2 KiB
C
50 lines
1.2 KiB
C
#include "amplify_tommath_private.h"
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#ifdef AMPLIFY_BN_MP_REDUCE_2K_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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/* Modifications Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved. */
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/* reduces a modulo n where n is of the form 2**p - d */
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amplify_mp_err amplify_mp_reduce_2k(amplify_mp_int *a, const amplify_mp_int *n, amplify_mp_digit d)
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{
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amplify_mp_int q;
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amplify_mp_err err;
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int p;
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if ((err = amplify_mp_init(&q)) != AMPLIFY_MP_OKAY) {
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return err;
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}
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p = amplify_mp_count_bits(n);
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top:
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/* q = a/2**p, a = a mod 2**p */
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if ((err = amplify_mp_div_2d(a, p, &q, a)) != AMPLIFY_MP_OKAY) {
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goto LBL_ERR;
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}
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if (d != 1u) {
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/* q = q * d */
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if ((err = amplify_mp_mul_d(&q, d, &q)) != AMPLIFY_MP_OKAY) {
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goto LBL_ERR;
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}
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}
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/* a = a + q */
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if ((err = amplify_s_mp_add(a, &q, a)) != AMPLIFY_MP_OKAY) {
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goto LBL_ERR;
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}
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if (amplify_mp_cmp_mag(a, n) != AMPLIFY_MP_LT) {
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if ((err = amplify_s_mp_sub(a, n, a)) != AMPLIFY_MP_OKAY) {
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goto LBL_ERR;
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}
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goto top;
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}
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LBL_ERR:
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amplify_mp_clear(&q);
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return err;
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}
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#endif
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