tommath/bn_mp_rand.c

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#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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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
*
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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
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*/
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#if defined(MP_8BIT) || defined(MP_16BIT)
#define MP_GEN_RANDOM_SHIFT DIGIT_BIT
#else
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#if MP_GEN_RANDOM_MAX == 0xffffffffu
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#define MP_GEN_RANDOM_SHIFT 32
#elif MP_GEN_RANDOM_MAX == 32767
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/* SHRT_MAX */
#define MP_GEN_RANDOM_SHIFT 15
#elif MP_GEN_RANDOM_MAX == 2147483647
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/* INT_MAX */
#define MP_GEN_RANDOM_SHIFT 31
#elif !defined(MP_GEN_RANDOM_SHIFT)
#error Thou shalt define their own valid MP_GEN_RANDOM_SHIFT
#endif
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#endif
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/* makes a pseudo-random int of a given size */
static mp_digit s_gen_random(void)
{
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mp_digit d = 0, msk = 0;
do {
d <<= MP_GEN_RANDOM_SHIFT;
d |= ((mp_digit) MP_GEN_RANDOM());
msk <<= MP_GEN_RANDOM_SHIFT;
msk |= (MP_MASK & MP_GEN_RANDOM_MAX);
} while ((MP_MASK & msk) != MP_MASK);
d &= MP_MASK;
return d;
}
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int mp_rand(mp_int *a, int digits)
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{
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int res;
mp_digit d;
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mp_zero(a);
if (digits <= 0) {
return MP_OKAY;
}
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/* first place a random non-zero digit */
do {
d = s_gen_random();
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} while (d == 0u);
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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) {
if ((res = mp_lshd(a, 1)) != MP_OKAY) {
return res;
}
if ((res = mp_add_d(a, s_gen_random(), a)) != MP_OKAY) {
return res;
}
}
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return MP_OKAY;
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}
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#endif
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/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */