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1 #include <tommath.h> |
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2 #ifdef BN_MP_EXPT_D_C |
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2
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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 /* calculate c = a**b using a square-multiply algorithm */ |
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19 int mp_expt_d (mp_int * a, mp_digit b, mp_int * c) |
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20 { |
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21 int res, x; |
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22 mp_int g; |
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23 |
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24 if ((res = mp_init_copy (&g, a)) != MP_OKAY) { |
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25 return res; |
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26 } |
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27 |
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28 /* set initial result */ |
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29 mp_set (c, 1); |
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30 |
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31 for (x = 0; x < (int) DIGIT_BIT; x++) { |
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32 /* square */ |
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33 if ((res = mp_sqr (c, c)) != MP_OKAY) { |
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34 mp_clear (&g); |
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35 return res; |
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36 } |
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37 |
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38 /* if the bit is set multiply */ |
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39 if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) { |
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40 if ((res = mp_mul (c, &g, c)) != MP_OKAY) { |
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41 mp_clear (&g); |
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42 return res; |
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43 } |
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44 } |
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45 |
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46 /* shift to next bit */ |
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47 b <<= 1; |
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48 } |
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49 |
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50 mp_clear (&g); |
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51 return MP_OKAY; |
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52 } |
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142
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53 #endif |
