Mercurial > dropbear

annotate libtommath/bn_mp_sub.c @ 1734:73646de50f13 DROPBEAR_2020.80

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version 2020.80
author Matt Johnston <matt@ucc.asn.au>
date Fri, 26 Jun 2020 21:45:59 +0800
parents 1051e4eea25a
children
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1655
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
Steffen Jaeckel <s_jaeckel@gmx.de>
parents: 1470
diff changeset
1 #include "tommath_private.h"
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2 #ifdef BN_MP_SUB_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 /* high level subtraction (handles signs) */
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7 mp_err mp_sub(const mp_int *a, const mp_int *b, mp_int *c)
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8 {
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9 mp_sign sa = a->sign, sb = b->sign;
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10 mp_err err;
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11
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Steffen Jaeckel <s_jaeckel@gmx.de>
parents: 1470
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12 if (sa != sb) {
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
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13 /* subtract a negative from a positive, OR */
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parents: 1470
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14 /* subtract a positive from a negative. */
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parents: 1470
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15 /* In either case, ADD their magnitudes, */
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parents: 1470
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16 /* and use the sign of the first number. */
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17 c->sign = sa;
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18 err = s_mp_add(a, b, c);
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parents: 1470
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19 } else {
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parents: 1470
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20 /* subtract a positive from a positive, OR */
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parents: 1470
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21 /* subtract a negative from a negative. */
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parents: 1470
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22 /* First, take the difference between their */
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parents: 1470
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23 /* magnitudes, then... */
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parents: 1470
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24 if (mp_cmp_mag(a, b) != MP_LT) {
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parents: 1470
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25 /* Copy the sign from the first */
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parents: 1470
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26 c->sign = sa;
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parents: 1470
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27 /* The first has a larger or equal magnitude */
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28 err = s_mp_sub(a, b, c);
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parents: 1470
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29 } else {
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parents: 1470
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30 /* The result has the *opposite* sign from */
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parents: 1470
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31 /* the first number. */
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32 c->sign = (sa == MP_ZPOS) ? MP_NEG : MP_ZPOS;
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parents: 1470
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33 /* The second has a larger magnitude */
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34 err = s_mp_sub(b, a, c);
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parents: 1470
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35 }
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36 }
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37 return err;
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38 }
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40 #endif