--- /dev/null
+/* TomsFastMath, a fast ISO C bignum library.
+ *
+ * This project is meant to fill in where LibTomMath
+ * falls short. That is speed ;-)
+ *
+ * This project is public domain and free for all purposes.
+ *
+ * Tom St Denis, tomstdenis@gmail.com
+ */
+#include <tfm_private.h>
+
+/* Miller-Rabin test of "a" to the base of "b" as described in
+ * HAC pp. 139 Algorithm 4.24
+ *
+ * Sets result to 0 if definitely composite or 1 if probably prime.
+ * Randomly the chance of error is no more than 1/4 and often
+ * very much lower.
+ */
+void fp_prime_miller_rabin (fp_int * a, fp_int * b, int *result)
+{
+ fp_int n1, y, r;
+ int s, j;
+
+ /* default */
+ *result = FP_NO;
+
+ /* ensure b > 1 */
+ if (fp_cmp_d(b, 1) != FP_GT) {
+ return;
+ }
+
+ /* get n1 = a - 1 */
+ fp_init_copy(&n1, a);
+ fp_sub_d(&n1, 1, &n1);
+
+ /* set 2**s * r = n1 */
+ fp_init_copy(&r, &n1);
+
+ /* count the number of least significant bits
+ * which are zero
+ */
+ s = fp_cnt_lsb(&r);
+
+ /* now divide n - 1 by 2**s */
+ fp_div_2d (&r, s, &r, NULL);
+
+ /* compute y = b**r mod a */
+ fp_init(&y);
+ fp_exptmod(b, &r, a, &y);
+
+ /* if y != 1 and y != n1 do */
+ if (fp_cmp_d (&y, 1) != FP_EQ && fp_cmp (&y, &n1) != FP_EQ) {
+ j = 1;
+ /* while j <= s-1 and y != n1 */
+ while ((j <= (s - 1)) && fp_cmp (&y, &n1) != FP_EQ) {
+ fp_sqrmod (&y, a, &y);
+
+ /* if y == 1 then composite */
+ if (fp_cmp_d (&y, 1) == FP_EQ) {
+ return;
+ }
+ ++j;
+ }
+
+ /* if y != n1 then composite */
+ if (fp_cmp (&y, &n1) != FP_EQ) {
+ return;
+ }
+ }
+
+ /* probably prime now */
+ *result = FP_YES;
+}
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */