1 #include "tommath_private.h"
2 #ifdef BN_MP_PRIME_NEXT_PRIME_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
4 /* SPDX-License-Identifier: Unlicense */
6 /* finds the next prime after the number "a" using "t" trials
9 * bbs_style = 1 means the prime must be congruent to 3 mod 4
11 mp_err mp_prime_next_prime(mp_int *a, int t, int bbs_style)
17 mp_digit res_tab[PRIVATE_MP_PRIME_TAB_SIZE], step, kstep;
23 /* simple algo if a is less than the largest prime in the table */
24 if (mp_cmp_d(a, s_mp_prime_tab[PRIVATE_MP_PRIME_TAB_SIZE-1]) == MP_LT) {
25 /* find which prime it is bigger than "a" */
26 for (x = 0; x < PRIVATE_MP_PRIME_TAB_SIZE; x++) {
27 cmp = mp_cmp_d(a, s_mp_prime_tab[x]);
32 if ((bbs_style == 1) && ((s_mp_prime_tab[x] & 3u) != 3u)) {
33 /* try again until we get a prime congruent to 3 mod 4 */
36 mp_set(a, s_mp_prime_tab[x]);
41 /* fall through to the sieve */
44 /* generate a prime congruent to 3 mod 4 or 1/3 mod 4? */
51 /* at this point we will use a combination of a sieve and Miller-Rabin */
54 /* if a mod 4 != 3 subtract the correct value to make it so */
55 if ((a->dp[0] & 3u) != 3u) {
56 if ((err = mp_sub_d(a, (a->dp[0] & 3u) + 1u, a)) != MP_OKAY) {
63 if ((err = mp_sub_d(a, 1uL, a)) != MP_OKAY) {
69 /* generate the restable */
70 for (x = 1; x < PRIVATE_MP_PRIME_TAB_SIZE; x++) {
71 if ((err = mp_mod_d(a, s_mp_prime_tab[x], res_tab + x)) != MP_OKAY) {
76 /* init temp used for Miller-Rabin Testing */
77 if ((err = mp_init(&b)) != MP_OKAY) {
82 /* skip to the next non-trivially divisible candidate */
85 /* y == 1 if any residue was zero [e.g. cannot be prime] */
88 /* increase step to next candidate */
91 /* compute the new residue without using division */
92 for (x = 1; x < PRIVATE_MP_PRIME_TAB_SIZE; x++) {
93 /* add the step to each residue */
96 /* subtract the modulus [instead of using division] */
97 if (res_tab[x] >= s_mp_prime_tab[x]) {
98 res_tab[x] -= s_mp_prime_tab[x];
101 /* set flag if zero */
102 if (res_tab[x] == 0u) {
106 } while ((y == 1) && (step < (((mp_digit)1 << MP_DIGIT_BIT) - kstep)));
109 if ((err = mp_add_d(a, step, a)) != MP_OKAY) {
113 /* if didn't pass sieve and step == MP_MAX then skip test */
114 if ((y == 1) && (step >= (((mp_digit)1 << MP_DIGIT_BIT) - kstep))) {
118 if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) {