Mercurial > dropbear

annotate libtommath/bn_mp_reduce_2k_l.c @ 1667:986126448688

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Update remaining advise to edit options.h You should edit localoptions.h instead.
author Alexander Dahl <ada@thorsis.com>
date Tue, 10 Mar 2020 15:38:38 +0100
parents f52919ffd3b1
children 1051e4eea25a
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_REDUCE_2K_L_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
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4 *
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5 * LibTomMath is a library that provides multiple-precision
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6 * integer arithmetic as well as number theoretic functionality.
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7 *
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8 * The library was designed directly after the MPI library by
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9 * Michael Fromberger but has been written from scratch with
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10 * additional optimizations in place.
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11 *
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12 * SPDX-License-Identifier: Unlicense
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13 */
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14
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15 /* reduces a modulo n where n is of the form 2**p - d
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16 This differs from reduce_2k since "d" can be larger
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17 than a single digit.
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18 */
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19 int mp_reduce_2k_l(mp_int *a, const mp_int *n, const mp_int *d)
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20 {
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21 mp_int q;
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22 int p, res;
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23
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24 if ((res = mp_init(&q)) != MP_OKAY) {
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25 return res;
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26 }
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27
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28 p = mp_count_bits(n);
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29 top:
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30 /* q = a/2**p, a = a mod 2**p */
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31 if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
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32 goto LBL_ERR;
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33 }
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34
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35 /* q = q * d */
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36 if ((res = mp_mul(&q, d, &q)) != MP_OKAY) {
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37 goto LBL_ERR;
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38 }
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39
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40 /* a = a + q */
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41 if ((res = s_mp_add(a, &q, a)) != MP_OKAY) {
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42 goto LBL_ERR;
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43 }
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44
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45 if (mp_cmp_mag(a, n) != MP_LT) {
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46 if ((res = s_mp_sub(a, n, a)) != MP_OKAY) {
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47 goto LBL_ERR;
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48 }
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49 goto top;
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50 }
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51
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52 LBL_ERR:
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53 mp_clear(&q);
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54 return res;
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55 }
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56
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57 #endif
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58
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59 /* ref: HEAD -> master, tag: v1.1.0 */
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60 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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61 /* commit time: 2019-01-28 20:32:32 +0100 */