From d4fbeed6f7b17abfbe4d33260e65d7e7fd974933 Mon Sep 17 00:00:00 2001
From: Gareth Rees
Date: Thu, 16 May 2013 13:17:42 +0100
Subject: Eventclock has enough entropy on all the platforms we support that we
 can use it to choose the random number seed.

Copied from Perforce
 Change: 181855
 ServerID: perforce.ravenbrook.com

---
 mps/code/testlib.c | 39 ++++++++++-----------------------------
 1 file changed, 10 insertions(+), 29 deletions(-)

(limited to 'mps/code')

diff --git a/mps/code/testlib.c b/mps/code/testlib.c
index be7284ea3fa..dae807b59fb 100644
--- a/mps/code/testlib.c
+++ b/mps/code/testlib.c
@@ -8,6 +8,7 @@
  */
 
 #include "testlib.h"
+#include "clock.h" /* for EVENT_CLOCK */
 #include "mps.h"
 #include "misc.h" /* for NOOP */
 #include <math.h>
@@ -246,17 +247,15 @@ mps_addr_t rnd_addr(void)
  *    that's impossible.
  *    (2008..2010-03-22)
  *
- * 3. v3 states: when autogenerated from time(), the published state 
- *    (printf'd) is that *after* the 10 rnds.  Therefore you can get 
- *    the state easily, store it, re-use it, etc.
- *    (New from 2010-03-22, changelist 170093)
+ * 3. v3 states: the published state is the state *after* all
+ *    initialization is complete. Therefore you can easily store and
+ *    re-use the published state. (From 2010-03-22, changelist
+ *    170093).
  */
 
 void randomize(int argc, char *argv[])
 {
-  int i;
   int n;
-  unsigned long seedt;
   unsigned long seed0;
 
   if (argc > 1) {
@@ -266,29 +265,11 @@ void randomize(int argc, char *argv[])
            argv[0], seed0);
     rnd_state_set(seed0);
   } else {
-    /* time_t uses an arbitrary encoding, but hopefully the low order */
-    /* 31 bits will have at least one bit changed from run to run. */
-    seedt = 1 + (unsigned long)time(NULL) % (R_m - 1);
-
-    /* The value returned by time() on some OSs may simply be a 
-     * count of seconds: therefore successive runs may start with 
-     * nearby seeds, possibly differing only by 1.  So the first value
-     * returned by rnd() may differ by only 48271.  It is conceivable 
-     * that some tests might be able to 'spot' this pattern (for 
-     * example: by using the first rnd() value, mod 100M and rounded 
-     * to multiple of 1024K, as arena size in bytes).
-     * 
-     * So to mix it up a bit, we do a few iterations now.  How many?  
-     * Very roughly, 48271^2 is of the same order as 2^31, so two 
-     * iterations would make the characteristic difference similar to 
-     * the period.  Hey, let's go wild and do 10.
-     */
-    rnd_state_set(seedt);
-    for(i = 0; i < 10; i += 1) {
-      (void)rnd();
-    }
-
-    seed0 = rnd_state();
+    /* Initialize seed based on seconds since epoch and on processor
+     * cycle count. */
+    EventClock t2;
+    EVENT_CLOCK(t2);
+    seed0 = 1 + ((unsigned long)time(NULL) + (unsigned long)t2) % (R_m - 1);
     printf("%s: randomize(): choosing initial state (v3): %lu.\n",
            argv[0], seed0);
     rnd_state_set(seed0);
-- 
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