81 lines
1.7 KiB
C
81 lines
1.7 KiB
C
#include <tommath_private.h>
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#ifdef BN_MP_RAND_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library was designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
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* additional optimizations in place.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tstdenis82@gmail.com, http://libtom.org
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*/
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#if MP_GEN_RANDOM_MAX == 0xffffffff
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#define MP_GEN_RANDOM_SHIFT 32
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#elif MP_GEN_RANDOM_MAX == 32767
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/* SHRT_MAX */
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#define MP_GEN_RANDOM_SHIFT 15
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#elif MP_GEN_RANDOM_MAX == 2147483647
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/* INT_MAX */
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#define MP_GEN_RANDOM_SHIFT 31
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#elif !defined(MP_GEN_RANDOM_SHIFT)
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#error Thou shalt define their own valid MP_GEN_RANDOM_SHIFT
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#endif
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/* makes a pseudo-random int of a given size */
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static mp_digit mp_gen_random(void)
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{
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mp_digit d = 0, msk = 0;
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do {
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d <<= MP_GEN_RANDOM_SHIFT;
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d |= ((mp_digit) MP_GEN_RANDOM());
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msk <<= MP_GEN_RANDOM_SHIFT;
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msk |= MP_GEN_RANDOM_MAX;
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} while ((MP_MASK & msk) != MP_MASK);
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d &= MP_MASK;
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return d;
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}
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int
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mp_rand (mp_int * a, int digits)
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{
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int res;
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mp_digit d;
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mp_zero (a);
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if (digits <= 0) {
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return MP_OKAY;
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}
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/* first place a random non-zero digit */
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do {
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d = mp_gen_random();
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} while (d == 0);
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if ((res = mp_add_d (a, d, a)) != MP_OKAY) {
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return res;
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}
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while (--digits > 0) {
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if ((res = mp_lshd (a, 1)) != MP_OKAY) {
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return res;
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}
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if ((res = mp_add_d (a, mp_gen_random(), a)) != MP_OKAY) {
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return res;
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}
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}
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return MP_OKAY;
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}
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#endif
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/* $Source$ */
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/* $Revision$ */
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/* $Date$ */
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