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annotate libtommath/bn_mp_mod_2d.c @ 1680:5e763ad6e2e0

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author Matt Johnston <matt@ucc.asn.au>
date Sun, 24 May 2020 13:34:19 +0800
parents f52919ffd3b1
children 1051e4eea25a
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_MOD_2D_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 /* calc a value mod 2**b */
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16 int mp_mod_2d(const mp_int *a, int b, mp_int *c)
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17 {
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18 int x, res;
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20 /* if b is <= 0 then zero the int */
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21 if (b <= 0) {
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22 mp_zero(c);
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23 return MP_OKAY;
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24 }
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26 /* if the modulus is larger than the value than return */
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27 if (b >= (a->used * DIGIT_BIT)) {
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28 res = mp_copy(a, c);
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29 return res;
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30 }
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32 /* copy */
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33 if ((res = mp_copy(a, c)) != MP_OKAY) {
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34 return res;
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35 }
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37 /* zero digits above the last digit of the modulus */
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38 for (x = (b / DIGIT_BIT) + (((b % DIGIT_BIT) == 0) ? 0 : 1); x < c->used; x++) {
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39 c->dp[x] = 0;
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40 }
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41 /* clear the digit that is not completely outside/inside the modulus */
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42 c->dp[b / DIGIT_BIT] &=
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43 ((mp_digit)1 << (mp_digit)(b % DIGIT_BIT)) - (mp_digit)1;
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44 mp_clamp(c);
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45 return MP_OKAY;
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46 }
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47 #endif
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48
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49 /* ref: HEAD -> master, tag: v1.1.0 */
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50 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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51 /* commit time: 2019-01-28 20:32:32 +0100 */