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1 /* LibTomMath, multiple-precision integer library -- Tom St Denis |
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2 * |
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3 * LibTomMath is a library that provides multiple-precision |
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4 * integer arithmetic as well as number theoretic functionality. |
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5 * |
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6 * The library was designed directly after the MPI library by |
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7 * Michael Fromberger but has been written from scratch with |
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8 * additional optimizations in place. |
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9 * |
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10 * The library is free for all purposes without any express |
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11 * guarantee it works. |
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12 * |
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13 * Tom St Denis, [email protected], http://math.libtomcrypt.org |
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14 */ |
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15 #include <tommath.h> |
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16 |
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17 /* high level addition (handles signs) */ |
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18 int mp_add (mp_int * a, mp_int * b, mp_int * c) |
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19 { |
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20 int sa, sb, res; |
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21 |
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22 /* get sign of both inputs */ |
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23 sa = a->sign; |
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24 sb = b->sign; |
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25 |
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26 /* handle two cases, not four */ |
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27 if (sa == sb) { |
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28 /* both positive or both negative */ |
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29 /* add their magnitudes, copy the sign */ |
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30 c->sign = sa; |
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31 res = s_mp_add (a, b, c); |
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32 } else { |
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33 /* one positive, the other negative */ |
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34 /* subtract the one with the greater magnitude from */ |
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35 /* the one of the lesser magnitude. The result gets */ |
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36 /* the sign of the one with the greater magnitude. */ |
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37 if (mp_cmp_mag (a, b) == MP_LT) { |
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38 c->sign = sb; |
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39 res = s_mp_sub (b, a, c); |
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40 } else { |
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41 c->sign = sa; |
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42 res = s_mp_sub (a, b, c); |
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43 } |
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44 } |
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45 return res; |
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46 } |
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47 |
