From 4ceefdbfedbb3bd959e77d21a7ea584b5145c076 Mon Sep 17 00:00:00 2001
From: ian <ian>
Date: Sun, 11 May 2008 22:27:34 +0000
Subject: [PATCH] get polarity right at the crossover

---
 hostside/safety.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/hostside/safety.c b/hostside/safety.c
index 2320dc1..4c1dcd3 100644
--- 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;
-- 
2.30.2