get polarity right at the crossover

diff --git a/hostside/safety.c b/hostside/safety.c
index 2320dc138dfa83adaff2892cacddc0a038d08c88..4c1dcd375152e764da8271660bc76d7b70f7bef8 100644 (file)
--- a/hostside/safety.c
+++ b/hostside/safety.c
@@ -172,6 +172,8 @@ Segment *segments;
  *   here now, pred. to have dep'd and ret'd    NPV  re-arrival    new, defer
  *   now absent, pred. to have arr, dep & ret'd         -PV  re-arrival    forbidden
  *
+ *  seg->tr_backwards records the sense of the _first_ passage of the train.
+ *
  *  invalid/impossible combination:
  *   train here now but never in prediction     N--
  *
@@ -370,6 +372,7 @@ static int initpresent_nextseg(TrackLocation *t, TrackAdvanceContext *c,
                               MovPosComb *mpc_io,
                               const TrackLocation *before) {
   PredictUserContext *u= c->u;
+  pred_callback_debug(" initpresent_nextseg",t,c,before);
   t->seg->now_present= t->seg->pred_present= t->seg->will_polarise= 1;
   t->seg->until= 0;
   if (!t->seg->i->invertible)
@@ -478,7 +481,8 @@ static int nose_nextseg(TrackLocation *t, TrackAdvanceContext *c,
 
  movement_ok:
   /* Now we definitely have a plan which sets a good route at t->seg. */
-  t->seg->tr_backwards= t->backwards;
+  if (!t->seg->pred_vacated)
+    t->seg->tr_backwards= t->backwards;
   t->seg->pred_present= 1;
   t->seg->until= u->elapsed;
   return 0; /* yay! */
@@ -493,8 +497,8 @@ static int tail_nextseg(TrackLocation *t, TrackAdvanceContext *c,
   if (!before) return 0;
   pred_callback_debug(" tail_nextseg",t,c,before);
 
-  if (!t->seg->i->invertible)
-    u->noninv_tally[before->seg->tr_backwards]--;
+  if (!before->seg->i->invertible)
+    u->noninv_tally[before->backwards]--;
 
   if (before->seg->pred_vacated) return 0; /* only vacate once */
   before->seg->pred_present= 0;