Mercurial > dropbear

annotate libtommath/bn_mp_rand.c @ 1482:6e09cb3d1230

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cast m_burn argument away from volatile
author Matt Johnston <matt@ucc.asn.au>
date Sat, 10 Feb 2018 00:12:22 +0800
parents 8bba51a55704
children f52919ffd3b1
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rev   line source
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1 #include <tommath_private.h>
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2 #ifdef BN_MP_RAND_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, [email protected], http://libtom.org
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16 */
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17
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18 #if MP_GEN_RANDOM_MAX == 0xffffffff
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19 #define MP_GEN_RANDOM_SHIFT 32
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20 #elif MP_GEN_RANDOM_MAX == 32767
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21 /* SHRT_MAX */
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22 #define MP_GEN_RANDOM_SHIFT 15
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23 #elif MP_GEN_RANDOM_MAX == 2147483647
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24 /* INT_MAX */
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25 #define MP_GEN_RANDOM_SHIFT 31
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26 #elif !defined(MP_GEN_RANDOM_SHIFT)
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27 #error Thou shalt define their own valid MP_GEN_RANDOM_SHIFT
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28 #endif
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29
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30 /* makes a pseudo-random int of a given size */
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31 static mp_digit s_gen_random(void)
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32 {
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33 mp_digit d = 0, msk = 0;
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34 do {
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35 d <<= MP_GEN_RANDOM_SHIFT;
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36 d |= ((mp_digit) MP_GEN_RANDOM());
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37 msk <<= MP_GEN_RANDOM_SHIFT;
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38 msk |= (MP_MASK & MP_GEN_RANDOM_MAX);
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39 } while ((MP_MASK & msk) != MP_MASK);
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40 d &= MP_MASK;
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41 return d;
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42 }
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43
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44 int
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45 mp_rand (mp_int * a, int digits)
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46 {
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47 int res;
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48 mp_digit d;
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49
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50 mp_zero (a);
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51 if (digits <= 0) {
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52 return MP_OKAY;
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53 }
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54
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55 /* first place a random non-zero digit */
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56 do {
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57 d = s_gen_random();
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58 } while (d == 0);
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59
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60 if ((res = mp_add_d (a, d, a)) != MP_OKAY) {
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61 return res;
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62 }
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63
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64 while (--digits > 0) {
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65 if ((res = mp_lshd (a, 1)) != MP_OKAY) {
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66 return res;
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67 }
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68
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69 if ((res = mp_add_d (a, s_gen_random(), a)) != MP_OKAY) {
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70 return res;
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71 }
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72 }
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73
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74 return MP_OKAY;
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75 }
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76 #endif
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77
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78 /* ref: $Format:%D$ */
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79 /* git commit: $Format:%H$ */
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80 /* commit time: $Format:%ai$ */