From 6505fd273a20a09c3a2f0992517a6f200c3f58e0 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Mon, 14 Jan 2019 15:53:04 +0000
Subject: [PATCH] wip break out edge_id_to_other_id

---
 parse-input-graph | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/parse-input-graph b/parse-input-graph
index e65df41..b3dfc84 100755
--- a/parse-input-graph
+++ b/parse-input-graph
@@ -155,7 +155,9 @@ sub edge_id_to_other_id ($$) {
   foreach my $adjib (0..$#$adjsb) {
     my $adjb = $adjsb->[$adjib];
     next unless $adjb->{Name} eq $ra;
-    return ($rb, $adjib);
+    # $adjb is the same edge seen from the other side
+    my $adjibc = ($adjib + 1) % @$adjsb;
+    return ($rb, $adjibc);
   }
   confess "$ra $adjia ?";
 }
@@ -179,7 +181,7 @@ sub dual () {
   foreach my $ra (sort keys %region) {
     my $adjsa = $region{$ra}{Adj};
     foreach my $adjia (0..$#$adjsa) {
-      my ($rb, $adjib) = edge_id_to_other_id($ra, $adjia);
+      my ($rb, $adjibc) = edge_id_to_other_id($ra, $adjia);
       my $adja = $adjsa->[$adjia];
       my $va = "$ra # $adjia";
       # $va is the vertex at the anticlockwise end
@@ -188,11 +190,9 @@ sub dual () {
 	      ($ra eq 'L' or $ra eq 'NZ');
       # $rb is the region on the other side of that edge
       my $adjsb = $region{$rb}{Adj};
-      # $adjb is the same edge seen from the other side
-      my $adjibc = ($adjib + 1) % @$adjsb;
       my $vb = "$rb # $adjibc";
       # $vb is the vertex at the *clockwise* end
-      # of that same edge, which is edge no $adjib of region $rb
+      # of that same edge, which is edge no.$adjibc of region $rb
       print STDERR "vertex $va = $vb\n";
       $g->add_edge($va,$vb);
       last;
-- 
2.30.2