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1 #include <tommath.h> |
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2 #ifdef BN_MP_2EXPT_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 /* computes a = 2**b |
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19 * |
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20 * Simple algorithm which zeroes the int, grows it then just sets one bit |
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21 * as required. |
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22 */ |
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23 int |
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24 mp_2expt (mp_int * a, int b) |
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25 { |
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26 int res; |
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27 |
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28 /* zero a as per default */ |
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29 mp_zero (a); |
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30 |
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31 /* grow a to accomodate the single bit */ |
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32 if ((res = mp_grow (a, b / DIGIT_BIT + 1)) != MP_OKAY) { |
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33 return res; |
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34 } |
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35 |
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36 /* set the used count of where the bit will go */ |
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37 a->used = b / DIGIT_BIT + 1; |
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38 |
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39 /* put the single bit in its place */ |
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40 a->dp[b / DIGIT_BIT] = ((mp_digit)1) << (b % DIGIT_BIT); |
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41 |
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42 return MP_OKAY; |
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43 } |
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142
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44 #endif |
