Mercurial > dropbear

annotate libtommath/bn_mp_add.c @ 374:87ae4565679d channel-fix

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merge of 'a94c5265558121fe936519b5d9a5eb27f95e9d9d' and 'd348546b80847bc0d42a7b5208bb31a54f1fdfaf'
author Matt Johnston <matt@ucc.asn.au>
date Tue, 05 Dec 2006 13:28:44 +0000
parents eed26cff980b
children 5ff8218bcee9
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284
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1 #include <tommath.h>
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2 #ifdef BN_MP_ADD_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 * The library is free for all purposes without any express
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13 * guarantee it works.
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14 *
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
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16 */
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17
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18 /* high level addition (handles signs) */
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19 int mp_add (mp_int * a, mp_int * b, mp_int * c)
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20 {
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21 int sa, sb, res;
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22
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23 /* get sign of both inputs */
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24 sa = a->sign;
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25 sb = b->sign;
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26
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27 /* handle two cases, not four */
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28 if (sa == sb) {
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29 /* both positive or both negative */
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30 /* add their magnitudes, copy the sign */
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31 c->sign = sa;
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32 res = s_mp_add (a, b, c);
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33 } else {
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34 /* one positive, the other negative */
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35 /* subtract the one with the greater magnitude from */
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36 /* the one of the lesser magnitude. The result gets */
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37 /* the sign of the one with the greater magnitude. */
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38 if (mp_cmp_mag (a, b) == MP_LT) {
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39 c->sign = sb;
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40 res = s_mp_sub (b, a, c);
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41 } else {
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42 c->sign = sa;
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43 res = s_mp_sub (a, b, c);
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44 }
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45 }
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46 return res;
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47 }
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48
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49 #endif