More efficient Rabin-Miller test: with random witnesses, skip redundant

[u/mdw/catacomb] / pgen.c

diff --git a/pgen.c b/pgen.c
index 74a10bc..dca61d9 100644 (file)
--- a/pgen.c
+++ b/pgen.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: pgen.c,v 1.7 2001/02/03 16:05:32 mdw Exp $
+ * $Id: pgen.c,v 1.8 2002/01/13 13:42:53 mdw Exp $
  *
  * Prime generation glue
  *
@@ -30,6 +30,10 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: pgen.c,v $
+ * Revision 1.8  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 1.7  2001/02/03 16:05:32  mdw
  * Now @mp_drop@ checks its argument is non-NULL before attempting to free
  * it.  Note that the macro version @MP_DROP@ doesn't do this.
@@ -145,11 +149,15 @@ int pgen_test(int rq, pgen_event *ev, void *p)
       rabin_create(r, ev->m);
       rc = PGEN_TRY;
       break;
-    case PGEN_TRY: {
-      mp *a = mprand_range(MP_NEW, ev->m, ev->r, 0);
-      rc = rabin_test(r, a);
-      mp_drop(a);
-    } break;
+    case PGEN_TRY:
+      if (!ev->tests)
+       rc = rabin_rtest(r, MP_TWO);
+      else {
+       mp *a = mprand_range(MP_NEW, ev->m, ev->r, 0);
+       rc = rabin_rtest(r, a);
+       mp_drop(a);
+      }
+      break;
     case PGEN_DONE:
       rabin_destroy(r);
       rc = PGEN_DONE;
@@ -197,8 +205,8 @@ mp *pgen(const char *name, mp *d, mp *m, pgen_proc *event, void *ectx,
     ev.m = MP_COPY(m);
   else
     ev.m = 0;
-  ev.steps = steps;
-  ev.tests = tests;
+  ev.steps = 0;
+  ev.tests = 0;
   ev.r = fibrand_create(0);
 
   /* --- Tell the event handler we're under way --- */
@@ -274,17 +282,17 @@ mp *pgen(const char *name, mp *d, mp *m, pgen_proc *event, void *ectx,
     /* --- If decrementing counters is requested, do that --- */
 
     if ((act & A_STEP) && steps) {
-      ev.steps--;
-      if (!ev.steps) {
+      ev.steps++;
+      if (ev.steps == steps) {
        act |= A_EVENT | A_ENDSTEP | A_DONE;
        rc = PGEN_ABORT;
       }
-      ev.tests = tests;
+      ev.tests = 0;
     }
 
     if ((act & A_TEST) && tests) {
-      ev.tests--;
-      if (!ev.tests) {
+      ev.tests++;
+      if (ev.tests == tests) {
        act |= A_ENDTEST | A_ENDSTEP | A_DONE;
        rc = PGEN_DONE;
       }