/* -*-c-*-
*
- * $Id: rabin.c,v 1.3 1999/12/22 15:50:29 mdw Exp $
+ * $Id: rabin.c,v 1.7 2002/01/13 13:42:53 mdw Exp $
*
* Miller-Rabin primality test
*
/*----- Revision history --------------------------------------------------*
*
* $Log: rabin.c,v $
+ * Revision 1.7 2002/01/13 13:42:53 mdw
+ * More efficient Rabin-Miller test: with random witnesses, skip redundant
+ * Montgomerization. (Being bijective, it can't affect the distribution.)
+ *
+ * Revision 1.6 2001/06/16 12:56:38 mdw
+ * Fixes for interface change to @mpmont_expr@ and @mpmont_mexpr@.
+ *
+ * Revision 1.5 2000/10/08 12:11:22 mdw
+ * Use @MP_EQ@ instead of @MP_CMP@.
+ *
+ * Revision 1.4 2000/06/22 19:03:02 mdw
+ * Use the new @mp_odd@ function.
+ *
* Revision 1.3 1999/12/22 15:50:29 mdw
* Reworking for new prime-search system. Add function for working out how
* many iterations to use for a particular number.
void rabin_create(rabin *r, mp *m)
{
mp *m1 = mp_sub(MP_NEW, m, MP_ONE);
- mpscan sc;
- size_t s;
-
- /* --- Find @r@ and @s@ --- */
-
mpmont_create(&r->mm, m);
- mp_scan(&sc, m1);
- s = 0;
- while (mp_step(&sc)) {
- if (mp_bit(&sc))
- break;
- s++;
- }
- r->s = s;
- r->r = mp_lsr(MP_NEW, m1, s);
-
- /* --- Compute %$(m - 1)R \bmod m$% --- */
-
+ r->r = mp_odd(MP_NEW, m1, &r->s);
r->m1 = mp_sub(MP_NEW, m, r->mm.r);
mp_drop(m1);
}
mpmont_destroy(&r->mm);
}
-/* --- @rabin_test@ --- *
+/* --- @rabin_test@, @rabin_rtest@ --- *
*
* Arguments: @rabin *r@ = pointer to Rabin-Miller context
* @mp *g@ = base to test the number against
* if it succeeded.
*
* Use: Performs a single iteration of the Rabin-Miller primality
- * test.
+ * test. The @rtest@ variant assumes that %$g$% is either
+ * already in Montgomery representation, or you don't care.
*/
-int rabin_test(rabin *r, mp *g)
+int rabin_rtest(rabin *r, mp *g)
{
mp *y;
mp *dd, *spare = MP_NEW;
*/
y = mpmont_expr(&r->mm, MP_NEW, g, r->r);
- if (MP_CMP(y, ==, r->mm.r) || MP_CMP(y, ==, r->m1)) {
+ if (MP_EQ(y, r->mm.r) || MP_EQ(y, r->m1)) {
rc = PGEN_PASS;
goto done;
}
dd = mp_sqr(spare, y);
dd = mpmont_reduce(&r->mm, dd, dd);
spare = y; y = dd;
- if (MP_CMP(y, ==, r->mm.r))
+ if (MP_EQ(y, r->mm.r))
break;
- if (MP_CMP(y, ==, r->m1)) {
+ if (MP_EQ(y, r->m1)) {
rc = PGEN_PASS;
break;
}
return (rc);
}
+int rabin_test(rabin *r, mp *g)
+{
+ int rc;
+ g = mpmont_mul(&r->mm, MP_NEW, g, r->mm.r2);
+ rc = rabin_rtest(r, g);
+ mp_drop(g);
+ return (rc);
+}
+
/* --- @rabin_iters@ --- *
*
* Arguments: @unsigned len@ = number of bits in value