X-Git-Url: https://git.distorted.org.uk/~mdw/catacomb/blobdiff_plain/3f078a9c1d674e911f8c4169930359d603ccd5fb..89717a56084f7cac56330c8527fbaff99b15709b:/math/pgen.c

diff --git a/math/pgen.c b/math/pgen.c
index 84185e33..f0606591 100644
--- a/math/pgen.c
+++ b/math/pgen.c
@@ -319,28 +319,33 @@ mp *pgen(const char *name, mp *d, mp *m, pgen_proc *event, void *ectx,
  *		@grand *gr@ = a random number source
  *
  * Returns:	Nonzero if @p@ is really prime.
+ *
+ * Use:		Checks the primality of @p@.  If @p@ is prime, then this
+ *		function returns nonzero; if @p@ is really composite then it
+ *		%%\emph{probably}%% returns zero, but might not.
+ *
+ *		Currently, this function uses the Baillie--PSW test, which
+ *		combines a single Miller--Rabin test with witness 2 with a
+ *		single Frobenius test with parameters chosen using
+ *		Selfridge's `Method A'.  No composites are known which pass
+ *		this test, though it's conjectured that infinitely many
+ *		exist.
  */
 
 int pgen_primep(mp *p, grand *gr)
 {
-  int i;
   rabin r;
-  mp *x = MP_NEW;
+  int rc;
 
   if (MP_NEGP(p)) return (0);
   switch (pfilt_smallfactor(p)) {
     case PGEN_DONE: return (1);
     case PGEN_FAIL: return (0);
   }
-  rabin_create(&r, p);
-  for (i = 32; i; i--) {
-    x = mprand_range(x, p, gr, 0);
-    if (rabin_rtest(&r, x) == PGEN_FAIL)
-      break;
-  }
-  MP_DROP(x);
-  rabin_destroy(&r);
-  return (!i);
+  rabin_create(&r, p); rc = rabin_test(&r, MP_TWO); rabin_destroy(&r);
+  if (rc == PGEN_FAIL) return (0);
+  rc = pgen_granfrob(p, 0, 0); if (rc == PGEN_FAIL) return (0);
+  return (1);
 }
 
 /*----- Test rig ----------------------------------------------------------*/