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-rw-r--r--libtommath/bn_mp_prime_next_prime.c288
1 files changed, 149 insertions, 139 deletions
diff --git a/libtommath/bn_mp_prime_next_prime.c b/libtommath/bn_mp_prime_next_prime.c
index bc31cc7..5973c4e 100644
--- a/libtommath/bn_mp_prime_next_prime.c
+++ b/libtommath/bn_mp_prime_next_prime.c
@@ -20,147 +20,157 @@
*
* bbs_style = 1 means the prime must be congruent to 3 mod 4
*/
-int mp_prime_next_prime(mp_int *a, int t, int bbs_style)
+int mp_prime_next_prime(mp_int * a, int t, int bbs_style)
{
- int err, res, x, y;
- mp_digit res_tab[PRIME_SIZE], step, kstep;
- mp_int b;
-
- /* ensure t is valid */
- if (t <= 0 || t > PRIME_SIZE) {
- return MP_VAL;
- }
-
- /* force positive */
- a->sign = MP_ZPOS;
-
- /* simple algo if a is less than the largest prime in the table */
- if (mp_cmp_d(a, ltm_prime_tab[PRIME_SIZE-1]) == MP_LT) {
- /* find which prime it is bigger than */
- for (x = PRIME_SIZE - 2; x >= 0; x--) {
- if (mp_cmp_d(a, ltm_prime_tab[x]) != MP_LT) {
- if (bbs_style == 1) {
- /* ok we found a prime smaller or
- * equal [so the next is larger]
- *
- * however, the prime must be
- * congruent to 3 mod 4
- */
- if ((ltm_prime_tab[x + 1] & 3) != 3) {
- /* scan upwards for a prime congruent to 3 mod 4 */
- for (y = x + 1; y < PRIME_SIZE; y++) {
- if ((ltm_prime_tab[y] & 3) == 3) {
- mp_set(a, ltm_prime_tab[y]);
- return MP_OKAY;
- }
- }
- }
- } else {
- mp_set(a, ltm_prime_tab[x + 1]);
- return MP_OKAY;
- }
- }
- }
- /* at this point a maybe 1 */
- if (mp_cmp_d(a, 1) == MP_EQ) {
- mp_set(a, 2);
- return MP_OKAY;
- }
- /* fall through to the sieve */
- }
-
- /* generate a prime congruent to 3 mod 4 or 1/3 mod 4? */
- if (bbs_style == 1) {
- kstep = 4;
- } else {
- kstep = 2;
- }
-
- /* at this point we will use a combination of a sieve and Miller-Rabin */
-
- if (bbs_style == 1) {
- /* if a mod 4 != 3 subtract the correct value to make it so */
- if ((a->dp[0] & 3) != 3) {
- if ((err = mp_sub_d(a, (a->dp[0] & 3) + 1, a)) != MP_OKAY) { return err; };
- }
- } else {
- if (mp_iseven(a) == 1) {
- /* force odd */
- if ((err = mp_sub_d(a, 1, a)) != MP_OKAY) {
- return err;
- }
- }
- }
-
- /* generate the restable */
- for (x = 1; x < PRIME_SIZE; x++) {
- if ((err = mp_mod_d(a, ltm_prime_tab[x], res_tab + x)) != MP_OKAY) {
- return err;
- }
- }
-
- /* init temp used for Miller-Rabin Testing */
- if ((err = mp_init(&b)) != MP_OKAY) {
- return err;
- }
-
- for (;;) {
- /* skip to the next non-trivially divisible candidate */
- step = 0;
- do {
- /* y == 1 if any residue was zero [e.g. cannot be prime] */
- y = 0;
-
- /* increase step to next candidate */
- step += kstep;
-
- /* compute the new residue without using division */
- for (x = 1; x < PRIME_SIZE; x++) {
- /* add the step to each residue */
- res_tab[x] += kstep;
-
- /* subtract the modulus [instead of using division] */
- if (res_tab[x] >= ltm_prime_tab[x]) {
- res_tab[x] -= ltm_prime_tab[x];
- }
-
- /* set flag if zero */
- if (res_tab[x] == 0) {
- y = 1;
- }
- }
- } while (y == 1 && step < ((((mp_digit)1)<<DIGIT_BIT) - kstep));
-
- /* add the step */
- if ((err = mp_add_d(a, step, a)) != MP_OKAY) {
- goto LBL_ERR;
- }
-
- /* if didn't pass sieve and step == MAX then skip test */
- if (y == 1 && step >= ((((mp_digit)1)<<DIGIT_BIT) - kstep)) {
- continue;
- }
-
- /* is this prime? */
- for (x = 0; x < t; x++) {
- mp_set(&b, ltm_prime_tab[x]);
- if ((err = mp_prime_miller_rabin(a, &b, &res)) != MP_OKAY) {
- goto LBL_ERR;
- }
- if (res == MP_NO) {
- break;
- }
- }
-
- if (res == MP_YES) {
- break;
- }
- }
-
- err = MP_OKAY;
+ int err, res, x, y;
+ mp_digit res_tab[PRIME_SIZE], step, kstep;
+ mp_int b;
+
+ /* ensure t is valid */
+ if (t <= 0 || t > PRIME_SIZE) {
+ return MP_VAL;
+ }
+
+ /* force positive */
+ a->sign = MP_ZPOS;
+
+ /* simple algo if a is less than the largest prime in the table */
+ if (mp_cmp_d(a, ltm_prime_tab[PRIME_SIZE - 1]) == MP_LT) {
+ /* find which prime it is bigger than */
+ for (x = PRIME_SIZE - 2; x >= 0; x--) {
+ if (mp_cmp_d(a, ltm_prime_tab[x]) != MP_LT) {
+ if (bbs_style == 1) {
+ /* ok we found a prime smaller or
+ * equal [so the next is larger]
+ *
+ * however, the prime must be
+ * congruent to 3 mod 4
+ */
+ if ((ltm_prime_tab[x + 1] & 3) != 3) {
+ /* scan upwards for a prime congruent to 3 mod 4 */
+ for (y = x + 1; y < PRIME_SIZE;
+ y++) {
+ if ((ltm_prime_tab[y] &
+ 3) == 3) {
+ mp_set(a,
+ ltm_prime_tab
+ [y]);
+ return MP_OKAY;
+ }
+ }
+ }
+ } else {
+ mp_set(a, ltm_prime_tab[x + 1]);
+ return MP_OKAY;
+ }
+ }
+ }
+ /* at this point a maybe 1 */
+ if (mp_cmp_d(a, 1) == MP_EQ) {
+ mp_set(a, 2);
+ return MP_OKAY;
+ }
+ /* fall through to the sieve */
+ }
+
+ /* generate a prime congruent to 3 mod 4 or 1/3 mod 4? */
+ if (bbs_style == 1) {
+ kstep = 4;
+ } else {
+ kstep = 2;
+ }
+
+ /* at this point we will use a combination of a sieve and Miller-Rabin */
+
+ if (bbs_style == 1) {
+ /* if a mod 4 != 3 subtract the correct value to make it so */
+ if ((a->dp[0] & 3) != 3) {
+ if ((err =
+ mp_sub_d(a, (a->dp[0] & 3) + 1, a)) != MP_OKAY) {
+ return err;
+ };
+ }
+ } else {
+ if (mp_iseven(a) == 1) {
+ /* force odd */
+ if ((err = mp_sub_d(a, 1, a)) != MP_OKAY) {
+ return err;
+ }
+ }
+ }
+
+ /* generate the restable */
+ for (x = 1; x < PRIME_SIZE; x++) {
+ if ((err =
+ mp_mod_d(a, ltm_prime_tab[x], res_tab + x)) != MP_OKAY) {
+ return err;
+ }
+ }
+
+ /* init temp used for Miller-Rabin Testing */
+ if ((err = mp_init(&b)) != MP_OKAY) {
+ return err;
+ }
+
+ for (;;) {
+ /* skip to the next non-trivially divisible candidate */
+ step = 0;
+ do {
+ /* y == 1 if any residue was zero [e.g. cannot be prime] */
+ y = 0;
+
+ /* increase step to next candidate */
+ step += kstep;
+
+ /* compute the new residue without using division */
+ for (x = 1; x < PRIME_SIZE; x++) {
+ /* add the step to each residue */
+ res_tab[x] += kstep;
+
+ /* subtract the modulus [instead of using division] */
+ if (res_tab[x] >= ltm_prime_tab[x]) {
+ res_tab[x] -= ltm_prime_tab[x];
+ }
+
+ /* set flag if zero */
+ if (res_tab[x] == 0) {
+ y = 1;
+ }
+ }
+ } while (y == 1
+ && step < ((((mp_digit) 1) << DIGIT_BIT) - kstep));
+
+ /* add the step */
+ if ((err = mp_add_d(a, step, a)) != MP_OKAY) {
+ goto LBL_ERR;
+ }
+
+ /* if didn't pass sieve and step == MAX then skip test */
+ if (y == 1 && step >= ((((mp_digit) 1) << DIGIT_BIT) - kstep)) {
+ continue;
+ }
+
+ /* is this prime? */
+ for (x = 0; x < t; x++) {
+ mp_set(&b, ltm_prime_tab[x]);
+ if ((err =
+ mp_prime_miller_rabin(a, &b, &res)) != MP_OKAY) {
+ goto LBL_ERR;
+ }
+ if (res == MP_NO) {
+ break;
+ }
+ }
+
+ if (res == MP_YES) {
+ break;
+ }
+ }
+
+ err = MP_OKAY;
LBL_ERR:
- mp_clear(&b);
- return err;
+ mp_clear(&b);
+ return err;
}
#endif
generated by cgit (git 2.34.1) at 2024-05-20 10:24:02 +0000