From 111cf87163baf82add9a089a10106966eb919cf2 Mon Sep 17 00:00:00 2001
From: Helmut Merz <helmutm@cy55.de>
Date: Sun, 27 Sep 2026 18:23:23 +0200
Subject: [PATCH] csys/space:neighbors: improvements

---
 csys/space.lisp     | 33 ++++++++++++++++++---------------
 test/test-csys.lisp |  4 ++--
 2 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/csys/space.lisp b/csys/space.lisp
index c5fa682..ab8e8bb 100644
--- a/csys/space.lisp
+++ b/csys/space.lisp
@@ -31,10 +31,9 @@
   nil)
 
 (defun neighbors (spc loc &key (dist 2))
-  (let* ((to (floor (sqrt dist)))
-         (from (- to))
+  (let* ((range (floor (sqrt dist)))
          nbrs)
-    (util:with-iterator (loc-iterator from to)
+    (util:with-iterator (loc-iterator range)
       (lambda (rloc)
         (let* ((cloc (loc-add rloc loc))
                (cell (fetch spc cloc)))
@@ -45,21 +44,25 @@
 
 (defun distance-sq (spc loc1 loc2))
 
-(defun loc-iterator (from to &key (dim 2))
-  (labels (
-    (inc (cur idx)
-      (when (< idx dim)
-        (let ((new (1+ (aref cur idx))))
-          (setf (aref cur idx) new)
-          (when (> new to)
-            (setf (aref cur idx) from)
-            (setf cur (inc cur (1+ idx))))
-          cur))))
-    (let ((cur (make-array dim :initial-element from)))
+(defun loc-iterator (range &key (dim 2))
+  (let* ((from (- range))
+         (zero (make-array dim :initial-element 0))
+         (cur (make-array dim :initial-element from)))
+    (labels (
+      (inc (cur &optional (idx 0))
+        (when (< idx dim)
+          (let ((new (1+ (aref cur idx))))
+            (setf (aref cur idx) new)
+            (when (> new range)
+              (setf (aref cur idx) from)
+              (setf cur (inc cur (1+ idx))))
+            cur))))
       (lambda ()
+        (when (equalp cur zero)
+          (setf cur (inc cur)))
         (when cur
           (prog1 (make-array dim :initial-contents cur)
-            (setf cur (inc cur 0))))))))
+            (setf cur (inc cur))))))))
 
 (defun loc-add (l1 l2)
   (let* ((dim (car (array-dimensions l1)))
diff --git a/test/test-csys.lisp b/test/test-csys.lisp
index 4c33e9a..21d34b3 100644
--- a/test/test-csys.lisp
+++ b/test/test-csys.lisp
@@ -88,10 +88,10 @@
     (== (space:fetch spc #(1 2)) 46)
     (space:del spc #(1 1))
     (== (space:fetch spc #(1 1)) nil)
-    (util:with-iterator (space:loc-iterator -1 1)
+    (util:with-iterator (space:loc-iterator 1)
       (lambda (loc)
         (push loc locs)))
-    (== (length locs) 9)
+    (== (length locs) 8)
     (== (car locs) #(1 1))
     (== (car (last locs)) #(-1 -1))
     (== (car (space:neighbors spc #(1 1))) 46)