From a6151f185fb2d061d858c436fb2665b4edfe0e0e Mon Sep 17 00:00:00 2001
From: Zeno Rogue <zeno@attnam.com>
Date: Sun, 8 Aug 2021 19:13:09 +0200
Subject: [PATCH] refactored whirlline loop detection

---
 complex.cpp     |  4 ++--
 complex2.cpp    |  8 +-------
 environment.cpp | 21 +++++++++++++++++++++
 3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/complex.cpp b/complex.cpp
index 28645e03..e03b94bc 100644
--- a/complex.cpp
+++ b/complex.cpp
@@ -102,6 +102,7 @@ EX namespace whirlwind {
     again: 
     cell *at = whirlline[isize(whirlline)-1];
     cell *prev = whirlline[isize(whirlline)-2];
+    if(looped(whirlline)) return;
     for(int i=0; i<at->type; i++) 
       if(at->move(i) && (euclid || at->move(i)->master->alt) && celldistAlt(at->move(i)) == d && at->move(i) != prev) {
         whirlline.push_back(at->move(i));
@@ -1062,10 +1063,9 @@ EX namespace whirlpool {
     again: 
     cell *at = whirlline[isize(whirlline)-1];
     cell *prev = whirlline[isize(whirlline)-2];
+    if(looped(whirlline)) return;
     for(int i=0; i<at->type; i++) 
       if(at->move(i) && (eubinary || at->move(i)->master->alt) && celldistAlt(at->move(i)) == d && at->move(i) != prev) {
-        if(at->move(i) == whirlline[0]) return; // loops in weird geometries?
-        if(at->move(i) == whirlline[isize(whirlline)/2]) return; // even weirder geometry?
         whirlline.push_back(at->move(i));
         goto again;
         }
diff --git a/complex2.cpp b/complex2.cpp
index f11c3dec..676b2f74 100644
--- a/complex2.cpp
+++ b/complex2.cpp
@@ -225,13 +225,7 @@ EX namespace westwall {
     again: 
     cell *at = whirlline[isize(whirlline)-1];
     cell *prev = whirlline[isize(whirlline)-2];
-    if(isize(whirlline) > 2 && at == whirlline[isize(whirlline)/2]) {
-      /* something weird must have happened... */
-      static bool once = true;
-      if(once) addMessage("warning: a bug in building a whirl line");
-      once = false;
-      return;
-      }
+    if(looped(whirlline)) return;
     for(int i=0; i<at->type; i++) 
       if(at->move(i) && coastvalEdge1(at->move(i)) == d && at->move(i) != prev) {
         whirlline.push_back(at->move(i));
diff --git a/environment.cpp b/environment.cpp
index 3cfa6999..a2508c5a 100644
--- a/environment.cpp
+++ b/environment.cpp
@@ -865,4 +865,25 @@ EX void monstersTurn() {
 #endif
   }
 
+/** check if whirlline is looped, if yes, remove the repeat; may not detect loops immediately */
+EX bool looped(vector<cell*>& whirlline) {
+  if(isize(whirlline) == 1)
+    return false;
+  if(whirlline.back() == whirlline.front()) {
+    whirlline.pop_back();
+    return true;
+    }
+  int pos = isize(whirlline)/2;
+  if(isize(whirlline) > 2 && whirlline.back() == whirlline[pos]) {
+    while(pos && whirlline.back() == whirlline[pos])
+      whirlline.pop_back();
+    /* something weird must have happened... */
+    static bool once = true;
+    if(once) addMessage("warning: a looped line");
+    once = false;
+    return true;
+    }
+  return false;
+  }
+
 }