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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 multiplication (handles sign) */ |
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18 int mp_mul (mp_int * a, mp_int * b, mp_int * c) |
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19 { |
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20 int res, neg; |
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21 neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG; |
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22 |
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23 /* use Toom-Cook? */ |
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24 if (MIN (a->used, b->used) >= TOOM_MUL_CUTOFF) { |
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25 res = mp_toom_mul(a, b, c); |
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26 /* use Karatsuba? */ |
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27 } else if (MIN (a->used, b->used) >= KARATSUBA_MUL_CUTOFF) { |
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28 res = mp_karatsuba_mul (a, b, c); |
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29 } else { |
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30 /* can we use the fast multiplier? |
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31 * |
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32 * The fast multiplier can be used if the output will |
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33 * have less than MP_WARRAY digits and the number of |
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34 * digits won't affect carry propagation |
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35 */ |
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36 int digs = a->used + b->used + 1; |
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37 |
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38 if ((digs < MP_WARRAY) && |
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39 MIN(a->used, b->used) <= |
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40 (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) { |
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41 res = fast_s_mp_mul_digs (a, b, c, digs); |
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42 } else { |
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43 res = s_mp_mul (a, b, c); |
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44 } |
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45 } |
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46 c->sign = neg; |
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47 return res; |
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48 } |
