X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/dfdacfdcd7e3376072506d6bdf69271a0e6bd2e0..6d56743beed37f62273209341fa812bcd6aa220f:/rabin.c

diff --git a/rabin.c b/rabin.c
index 58d5291..915dc14 100644
--- a/rabin.c
+++ b/rabin.c
@@ -1,6 +1,6 @@
 /* -*-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
  *
@@ -30,6 +30,19 @@
 /*----- 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.
@@ -66,24 +79,8 @@
 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);
 }
@@ -105,7 +102,7 @@ void rabin_destroy(rabin *r)
   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
@@ -114,10 +111,11 @@ void rabin_destroy(rabin *r)
  *		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;
@@ -131,7 +129,7 @@ int rabin_test(rabin *r, mp *g)
    */
 
   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;
   }
@@ -146,9 +144,9 @@ int rabin_test(rabin *r, mp *g)
     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;
     }
@@ -163,6 +161,15 @@ done:
   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