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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 /* determines the setup value */ |
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18 int |
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19 mp_reduce_2k_setup(mp_int *a, mp_digit *d) |
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20 { |
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21 int res, p; |
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22 mp_int tmp; |
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23 |
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24 if ((res = mp_init(&tmp)) != MP_OKAY) { |
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25 return res; |
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26 } |
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27 |
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28 p = mp_count_bits(a); |
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29 if ((res = mp_2expt(&tmp, p)) != MP_OKAY) { |
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30 mp_clear(&tmp); |
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31 return res; |
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32 } |
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33 |
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34 if ((res = s_mp_sub(&tmp, a, &tmp)) != MP_OKAY) { |
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35 mp_clear(&tmp); |
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36 return res; |
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37 } |
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38 |
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39 *d = tmp.dp[0]; |
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40 mp_clear(&tmp); |
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41 return MP_OKAY; |
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42 } |
