Add cyclic group abstraction, with test code. Separate off exponentation

[u/mdw/catacomb] / pgen.c

diff --git a/pgen.c b/pgen.c
index eebd966..9cc4334 100644 (file)
--- a/pgen.c
+++ b/pgen.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: pgen.c,v 1.6 2000/10/08 12:11:22 mdw Exp $
+ * $Id: pgen.c,v 1.9 2004/04/01 12:50:09 mdw Exp $
  *
  * Prime generation glue
  *
@@ -30,6 +30,21 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: pgen.c,v $
+ * Revision 1.9  2004/04/01 12:50:09  mdw
+ * Add cyclic group abstraction, with test code.  Separate off exponentation
+ * functions for better static linking.  Fix a buttload of bugs on the way.
+ * Generally ensure that negative exponents do inversion correctly.  Add
+ * table of standard prime-field subgroups.  (Binary field subgroups are
+ * currently unimplemented but easy to add if anyone ever finds a good one.)
+ *
+ * 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.
+ *
  * Revision 1.6  2000/10/08 12:11:22  mdw
  * Use @MP_EQ@ instead of @MP_CMP@.
  *
@@ -141,11 +156,15 @@ 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;
@@ -193,8 +212,8 @@ 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 --- */
@@ -270,17 +289,17 @@ 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;
       }
@@ -317,12 +336,42 @@ mp *pgen(const char *name, mp *d, mp *m, pgen_proc *event, void *ectx,
     ev.m = 0;
   }
   ev.r->ops->destroy(ev.r);
-  if (d != MP_NEW)
-    mp_drop(d);
+  mp_drop(d);
 
   return (ev.m);
 }
 
+/* --- @pgen_primep@ --- *
+ *
+ * Arguments:  @mp *p@ = a number to check
+ *             @grand *gr@ = a random number source
+ *
+ * Returns:    Nonzero if @p@ is really prime.
+ */
+
+int pgen_primep(mp *p, grand *gr)
+{
+  int i = rabin_iters(mp_bits(p));
+  rabin r;
+  mp *x = MP_NEW;
+
+  if (MP_ISNEG(p)) return (0);
+  switch (pfilt_smallfactor(p)) {
+    case PGEN_DONE: return (1);
+    case PGEN_FAIL: return (0);
+  }
+  rabin_create(&r, p);
+  while (i) {
+    x = mprand_range(x, p, gr, 0);
+    if (rabin_rtest(&r, x) == PGEN_FAIL)
+      break;
+    i--;
+  }
+  MP_DROP(x);
+  rabin_destroy(&r);
+  return (!i);
+}
+
 /*----- Test rig ----------------------------------------------------------*/
 
 #ifdef TEST_RIG
@@ -353,8 +402,7 @@ static int verify(dstr *v)
 
   mp_drop(m);
   mp_drop(q);
-  if (p)
-    mp_drop(p);
+  mp_drop(p);
   assert(mparena_count(MPARENA_GLOBAL) == 0);
   return (ok);
 }