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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 /* computes a = 2**b |
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18 * |
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19 * Simple algorithm which zeroes the int, grows it then just sets one bit |
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20 * as required. |
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21 */ |
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22 int |
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23 mp_2expt (mp_int * a, int b) |
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24 { |
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25 int res; |
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26 |
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27 /* zero a as per default */ |
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28 mp_zero (a); |
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29 |
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30 /* grow a to accomodate the single bit */ |
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31 if ((res = mp_grow (a, b / DIGIT_BIT + 1)) != MP_OKAY) { |
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32 return res; |
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33 } |
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34 |
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35 /* set the used count of where the bit will go */ |
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36 a->used = b / DIGIT_BIT + 1; |
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37 |
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38 /* put the single bit in its place */ |
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39 a->dp[b / DIGIT_BIT] = 1 << (b % DIGIT_BIT); |
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40 |
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41 return MP_OKAY; |
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42 } |
