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annotate libtommath/bn_mp_xor.c @ 1934:83b6a47759a8

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Add m_snprintf() that won't return negative
author Matt Johnston <matt@ucc.asn.au>
date Fri, 01 Apr 2022 12:10:48 +0800
parents 1051e4eea25a
children
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_XOR_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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5
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6 /* two complement xor */
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7 mp_err mp_xor(const mp_int *a, const mp_int *b, mp_int *c)
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8 {
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9 int used = MP_MAX(a->used, b->used) + 1, i;
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10 mp_err err;
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11 mp_digit ac = 1, bc = 1, cc = 1;
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12 mp_sign csign = (a->sign != b->sign) ? MP_NEG : MP_ZPOS;
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13
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14 if (c->alloc < used) {
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15 if ((err = mp_grow(c, used)) != MP_OKAY) {
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16 return err;
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17 }
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18 }
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19
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20 for (i = 0; i < used; i++) {
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21 mp_digit x, y;
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22
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23 /* convert to two complement if negative */
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24 if (a->sign == MP_NEG) {
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25 ac += (i >= a->used) ? MP_MASK : (~a->dp[i] & MP_MASK);
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26 x = ac & MP_MASK;
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27 ac >>= MP_DIGIT_BIT;
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28 } else {
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29 x = (i >= a->used) ? 0uL : a->dp[i];
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30 }
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31
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32 /* convert to two complement if negative */
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33 if (b->sign == MP_NEG) {
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34 bc += (i >= b->used) ? MP_MASK : (~b->dp[i] & MP_MASK);
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35 y = bc & MP_MASK;
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36 bc >>= MP_DIGIT_BIT;
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37 } else {
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38 y = (i >= b->used) ? 0uL : b->dp[i];
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39 }
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40
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41 c->dp[i] = x ^ y;
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42
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43 /* convert to to sign-magnitude if negative */
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44 if (csign == MP_NEG) {
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45 cc += ~c->dp[i] & MP_MASK;
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46 c->dp[i] = cc & MP_MASK;
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47 cc >>= MP_DIGIT_BIT;
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48 }
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49 }
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50
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51 c->used = used;
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52 c->sign = csign;
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53 mp_clamp(c);
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54 return MP_OKAY;
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55 }
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56 #endif