tommath/bn_mp_prime_next_prime.c
2010-07-15 17:25:21 +02:00

55 lines
1.2 KiB
C

/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is library that provides for multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library is designed directly after the MPI library by
* 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.
*
* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
*/
#include <tommath.h>
/* finds the next prime after the number "a" using "t" trials
* of Miller-Rabin.
*/
int mp_prime_next_prime(mp_int *a, int t)
{
int err, res;
if (mp_iseven(a) == 1) {
/* force odd */
if ((err = mp_add_d(a, 1, a)) != MP_OKAY) {
return err;
}
} else {
/* force to next odd number */
if ((err = mp_add_d(a, 2, a)) != MP_OKAY) {
return err;
}
}
for (;;) {
/* is this prime? */
if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) {
return err;
}
if (res == 1) {
break;
}
/* add two, next candidate */
if ((err = mp_add_d(a, 2, a)) != MP_OKAY) {
return err;
}
}
return MP_OKAY;
}