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1 | #include <tommath.h> |
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2 | #ifdef BN_MP_EXPT_D_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, tomstdenis@gmail.com, http://math.libtomcrypt.com |
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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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53 | #endif |
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54 | |
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55 | /* $Source: /cvsroot/tcl/libtommath/bn_mp_expt_d.c,v $ */ |
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56 | /* $Revision: 1.1.1.3 $ */ |
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57 | /* $Date: 2006/12/01 00:08:11 $ */ |
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