tommath/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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* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
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*/
#include <tommath.h>
/* makes a pseudo-random int of a given size */
int
mp_rand (mp_int * a, int digits)
{
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int res;
mp_digit d;
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mp_zero (a);
if (digits <= 0) {
return MP_OKAY;
}
/* first place a random non-zero digit */
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do {
d = ((mp_digit) abs (rand ()));
} while (d == 0);
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if ((res = mp_add_d (a, d, a)) != MP_OKAY) {
return res;
}
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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if ((res = mp_add_d (a, ((mp_digit) abs (rand ())), a)) != MP_OKAY) {
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return res;
}
}
return MP_OKAY;
}