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annotate libtommath/bn_mp_mod_2d.c @ 1816:96d573b40bb4

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merge
author Matt Johnston <matt@ucc.asn.au>
date Wed, 31 Mar 2021 23:24:55 +0800
parents 1051e4eea25a
children
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
Steffen Jaeckel <s_jaeckel@gmx.de>
parents: 1470
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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 /* SPDX-License-Identifier: Unlicense */
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6 /* calc a value mod 2**b */
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7 mp_err mp_mod_2d(const mp_int *a, int b, mp_int *c)
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8 {
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9 int x;
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10 mp_err err;
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11
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parents: 1470
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12 /* if b is <= 0 then zero the int */
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parents: 1470
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13 if (b <= 0) {
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14 mp_zero(c);
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15 return MP_OKAY;
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parents: 1470
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16 }
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parents: 1470
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18 /* if the modulus is larger than the value than return */
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19 if (b >= (a->used * MP_DIGIT_BIT)) {
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20 return mp_copy(a, c);
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21 }
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23 /* copy */
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24 if ((err = mp_copy(a, c)) != MP_OKAY) {
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25 return err;
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26 }
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28 /* zero digits above the last digit of the modulus */
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29 x = (b / MP_DIGIT_BIT) + (((b % MP_DIGIT_BIT) == 0) ? 0 : 1);
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30 MP_ZERO_DIGITS(c->dp + x, c->used - x);
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32 /* clear the digit that is not completely outside/inside the modulus */
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33 c->dp[b / MP_DIGIT_BIT] &=
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34 ((mp_digit)1 << (mp_digit)(b % MP_DIGIT_BIT)) - (mp_digit)1;
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35 mp_clamp(c);
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36 return MP_OKAY;
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37 }
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38 #endif